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Needham, David

Overview:

Professor Needham also holds appointments as Associate Professor of Biomedical Engineering; Associate Professor, Center for Bioinspired materials and material Systems, and the Center for Biomolecular and Tissue Engineering; and Associate Professor, Duke Comprehensive Cancer Center.

Needham's Lab uses a platform technology of micropipette manipulation to manipulate single and pairs of micro particles in order to assess their behavior in well defined fluids and excipient concentrations. He brings a wealth of expertise in micromanipulation, colloid stability, and drug delivery formulation.

Positions:

Professor with Tenure in the Department of Mechanical Engineering and Materials Science

Mechanical Engineering and Materials Science
Pratt School of Engineering

Member of the Duke Cancer Institute

Duke Cancer Institute
School of Medicine

Education:

B.S. 1975

B.S. — Nottingham Trent University

Ph.D. 1981

Ph.D. — University of Nottingham

News:

Grants:

University Training Program in Biomolecular and Tissue Engineering

Administered By
Biomedical Engineering
AwardedBy
National Institutes of Health
Role
Mentor
Start Date
July 01, 1994
End Date
June 30, 2017

TRP and AQP Channels: Modulation of Function, Raft Location by Membrane Lipids

Administered By
Cell Biology
AwardedBy
National Institutes of Health
Role
Consultant
Start Date
July 01, 1980
End Date
August 31, 2015

PLGA Protein Microspheres: Single Particle Engineering

Administered By
Pratt School of Engineering
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
September 15, 2006
End Date
June 30, 2011

Faculty Development Workshop: "Course Enhancement Projects" Across the Pratt Curriculum

Administered By
Mechanical Engineering and Materials Science
AwardedBy
Lord Foundation of North Carolina
Role
Principal Investigator
Start Date
July 01, 2009
End Date
May 01, 2010

Integrating Nanoscale Systems and Design into the Undergraduate Engineering and Science Curricula

Administered By
Biomedical Engineering
AwardedBy
National Science Foundation
Role
Co-Principal Investigator
Start Date
May 01, 2007
End Date
April 30, 2010

Training in Biomolecular and Tissue Engineering

Administered By
Orthopaedics
AwardedBy
National Institutes of Health
Role
Mentor
Start Date
September 20, 2003
End Date
June 30, 2009

Ultra High-speed Imaging System

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Senior Investigator
Start Date
April 01, 2003
End Date
March 31, 2008

Graduate training in Biologically Inspired Materials

Administered By
Pratt School of Engineering
AwardedBy
National Science Foundation
Role
Co-Principal Investigator
Start Date
December 15, 2002
End Date
November 30, 2007

Thermally Sensitive Drug Delivery System for Tumors

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
June 01, 2000
End Date
May 31, 2006

Molecular Exchange with Lipid Membranes

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
July 01, 1995
End Date
August 31, 2005

Engineering Biology at the Nanoscale

Administered By
Pratt School of Engineering
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
September 30, 2004
End Date
July 31, 2005

Upgrade of a Shared Instrumentation Resource in the PSOE: The Laser Scanning Confocal Microscope

Administered By
Biomedical Engineering
AwardedBy
Lord Foundation of North Carolina
Role
Co-Principal Investigator
Start Date
May 31, 2002
End Date
June 30, 2005

Development and Construction of Single Molecule Spectrometers for Research and Student Training

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Science Foundation
Role
Co-Principal Investigator
Start Date
August 15, 2001
End Date
July 31, 2003

(95-0189) Molecular Forces in Blood-vasular Cell Interaction

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
July 13, 1995
End Date
June 30, 2000

(96-0807) Molecular Forces in Blood/Vascular Cell Adhesion

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
July 13, 1995
End Date
June 30, 2000

(97-0846) Molecular Forces in Blood/Vascular Cell Adhesion

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
July 13, 1995
End Date
June 30, 2000

(98-0573) Molecular Exchange and Defect Formation in Membranes

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
December 01, 1988
End Date
September 30, 1999

Particle Size Measurement: Instrumentation Grant

Administered By
Mechanical Engineering and Materials Science
AwardedBy
Lord Foundation of North Carolina
Role
Principal Investigator
Start Date
May 01, 1998
End Date
June 30, 1999

(94-1004) Molecular Exchange and Defect Formation in Membranes

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
December 01, 1988
End Date
March 31, 1999

(96-0604) Molecular Exchange and Defect Formation in Membranes

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
December 01, 1988
End Date
March 31, 1999

(97-0628) Molecular Exchange and Defect Formation in Membranes

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
December 01, 1988
End Date
March 31, 1999

(97-0933) ME265.03 Biological Materials Sci; Curriculum Development & Textbook...

Administered By
Mechanical Engineering and Materials Science
AwardedBy
Lord Foundation of North Carolina
Role
Principal Investigator
Start Date
June 01, 1997
End Date
May 31, 1998

(93-0137) Viscoelasticity of Blood Cells

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Co-Principal Investigator
Start Date
April 01, 1979
End Date
November 30, 1995

(95-0153) Viscoelasticity of Blood Cells

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Co-Principal Investigator
Start Date
April 01, 1979
End Date
November 30, 1995

(93-0073) Biorheology of Hybridomas and Cell Damage

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Science Foundation
Role
Co-Principal Investigator
Start Date
April 01, 1991
End Date
March 31, 1994

(87-0337) Electropermeabilization/Fusion of Liquid Vesicles and Cells

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
December 01, 1988
End Date
November 30, 1993

(90-0151) Electropermeabilitization/ Fusion of Lipid Vesicles and Cells

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
December 01, 1988
End Date
November 30, 1993

(91-0232) Electropermeabilization/Fusion of Lipid Vesicles and Cells

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
December 01, 1988
End Date
November 30, 1993

(92-0207) Electropermeabilization/Fusion of Lipid Vesicles & Cells

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
December 01, 1988
End Date
November 30, 1993

(93-0180) Electropermeabilization/Fusion of Lipid Vesicles and Cells

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Institutes of Health
Role
Principal Investigator
Start Date
December 01, 1988
End Date
November 30, 1993

(91-0174) Biorheology of Hybridomas and Cell Damage

Administered By
Mechanical Engineering and Materials Science
AwardedBy
National Science Foundation
Role
Co-Principal Investigator
Start Date
September 01, 1991
End Date
August 31, 1992
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Publications:

Real-Time Visualization of the Precipitation and Phase Behavior of Octaethylporphyrin in Lipid Microparticles.

The material properties of micro- and nanoparticles are fundamental for their bulk properties in suspension, like their stability and encapsulation efficiency. A particularly interesting system with potential biomedical applications is the encapsulation of hydrophobic porphyrins into lipid particles and their use as metal atom chelators, where retention and stability are keys for the design process. The overall goal here was to study the solubility, phase behavior, and mixing of octaethylporphyrin (OEP) and OEP-Cu chelates with 2 core materials, triolein (TO) and cholesteryl acetate, as single microparticles. We employed a real-time, single-particle microscopic technique based on micropipette injection to characterize the behavior of these materials and their mixtures upon solvent loss and precipitation. A clear phase separation was observed between the triolein liquid core and porphyrin microcrystals, and the ternary phase diagram of the droplet compositions and onsets of phase separation over solvent dissolution was built. On the contrary, cholesteryl acetate and OEP-Cu coprecipitated by solvent dissolution, preventing porphyrin crystallization even for very high supersaturations. This type of real-time, single-particle characterization is expected to offer important information about the formulation of other hydrophobic compounds of interest, where finding the proper encapsulation environment is a key step for their retention and stability.

Authors
Parra, E; Hervella, P; Needham, D
MLA Citation
Parra, E, Hervella, P, and Needham, D. "Real-Time Visualization of the Precipitation and Phase Behavior of Octaethylporphyrin in Lipid Microparticles." Journal of pharmaceutical sciences 106.4 (April 2017): 1025-1041.
PMID
27956095
Source
epmc
Published In
Journal of Pharmaceutical Sciences
Volume
106
Issue
4
Publish Date
2017
Start Page
1025
End Page
1041
DOI
10.1016/j.xphs.2016.11.019

New sensitive micro-measurements of dynamic surface tension and diffusion coefficients: Validated and tested for the adsorption of 1-Octanol at a microscopic air-water interface and its dissolution into water.

Currently available dynamic surface tension (DST) measurement methods, such as Wilhelmy plate, droplet- or bubble-based methods, still have various experimental limitations such as the large size of the interface, convection in the solution, or a certain "dead time" at initial measurement. These limitations create inconsistencies for the kinetic analysis of surfactant adsorption/desorption, especially significant for ionic surfactants. Here, the "micropipette interfacial area-expansion method" was introduced and validated as a new DST measurement having a high enough sensitivity to detect diffusion controlled molecular adsorption at the air-water interfaces. To validate the new technique, the diffusion coefficient of 1-Octanol in water was investigated with existing models: the Ward Tordai model for the long time adsorption regime (1-100s), and the Langmuir and Frumkin adsorption isotherm models for surface excess concentration. We found that the measured diffusion coefficient of 1-Octanol, 7.2±0.8×10-6cm2/s, showed excellent agreement with the result from an alternative method, "single microdroplet catching method", to measure the diffusion coefficient from diffusion-controlled microdroplet dissolution, 7.3±0.1×10-6cm2/s. These new techniques for determining adsorption and diffusion coefficients can apply for a range of surface active molecules, especially the less-characterized ionic surfactants, and biological compounds such as lipids, peptides, and proteins.

Authors
Kinoshita, K; Parra, E; Needham, D
MLA Citation
Kinoshita, K, Parra, E, and Needham, D. "New sensitive micro-measurements of dynamic surface tension and diffusion coefficients: Validated and tested for the adsorption of 1-Octanol at a microscopic air-water interface and its dissolution into water." Journal of colloid and interface science 488 (February 2017): 166-179.
PMID
27825061
Source
epmc
Published In
Journal of Colloid and Interface Science
Volume
488
Publish Date
2017
Start Page
166
End Page
179
DOI
10.1016/j.jcis.2016.10.052

An Activity-Based Dissolution Model for Solute-Containing Microdroplets.

When a solute is present in an aqueous droplet, the water activity in the droplet and the rate of droplet dissolution are both decreased (as compared to a pure water droplet). One of the main parameters that controls this effect is the dynamically changing solute concentration, and therefore water activity and chemical potential, at the droplet interface. This work addresses the importance of understanding how water activity changes during solution droplet dissolution. A model for dissolution rate is presented that accounts for the kinetic effects of changing water activity at the droplet interface during the dissolution of an aqueous salt solution microdroplet into a second immiscible liquid phase. The important underlying question in this model is whether the dissolving component can be considered in local equilibrium on both sides of the droplet interface and whether this assumption is sufficient to account for the kinetics of dissolution. The dissolution model is based on the Epstein-Plesset equation, which has previously been applied to pure gas (bubble) and liquid (droplet) dissolution into liquid phases, but not to salt solutions. The model is tested by using the micropipet technique to form and observe the dehydration of single NaCl solution microdroplets in octanol or butyl acetate. The model successfully predicts the droplet diameter as a function of time in both organic solvents. The NaCl concentration in water is measured well into the supersaturated area >5.4 M, and the supersaturation limit at which NaCl nucleation happens is reported to be 10.24 ± 0.31 M.

Authors
Bitterfield, DL; Utoft, A; Needham, D
MLA Citation
Bitterfield, DL, Utoft, A, and Needham, D. "An Activity-Based Dissolution Model for Solute-Containing Microdroplets." Langmuir : the ACS journal of surfaces and colloids 32.48 (December 2016): 12749-12759.
PMID
27802055
Source
epmc
Published In
Langmuir
Volume
32
Issue
48
Publish Date
2016
Start Page
12749
End Page
12759

Bottom up design of nanoparticles for anti-cancer diapeutics: "put the drug in the cancer's food".

The story starts in Basel at CLINAM in 2013, when I asked Pieter about making nanoparticles and he advised me to "try this solvent-exchange method we have developed for making limit sized particles". We are particularly interested in what are "limit size materials" because we want to test the feasibility of an idea: could we design, make, develop, and test the concept for treating metastatic cancer by, "Putting the Drug in the Cancer's Food? "Limit size" is the size of the cancer's food, ? the common Low Density Lipoprotein, (LDL) ~20 nm diameter. In this contribution to Pieter's LTAA we focus on the "bottom" (nucleation) and the "up" (growth) of "bottom-up design" as it applies to homogeneous nucleation of especially, hydrophobic drugs and the 8 physico-chemical stages and associated parameters that determine the initial size, and any subsequent coarsening, of a nanoparticle suspension. We show that, when made by the rapid solvent-exchange method, the same sized particles can be obtained without phospholipid. Furthermore, the obtained size follows the predictions of classic nucleation theory when the appropriate values for the parameters (surface tension and supersaturation) at nucleation are included. Calculations on dissolution time for nanoparticles reveal that a typical fewmicromolar-solubility, hydrophobic, anti-cancer drug (like Lapatinib, Niclosamide, Abiraterone, and Fulvestrant) of 500 nm diameter would take between 3?7 s to dissolve in an infinite sink like the blood stream; and a 50 nm particle would dissolve in less than a second! And so the nanoparticle design requires a highly water-insoluble drug, and a tight, encapsulating, impermeable lipid:cholesterol monolayer. While the "Y" junction can be used to mix an ethanolic solution with anti-solvent, we find that a "no-junction" can give equally good results. A series of nanoparticles (DiI-fluorescently labeled Triolein-cored and drug-cored nanoparticles of Orlistat) were then tested in well-characterized cell lines for uptake and efficacy as well as a PET-imageable nanoparticle in initial PET-imaging studies in animals for EPR uptake and tumor detection. We show that, while free-drug cannot be optimally administered in vivo, a nanoparticle formulation of orlistat could in principle represent a stable parenteral delivery system. The article ends with a brief discussion of what we see as the way forward in Individualized Medicine from the Diagnostic-Therapeutic ("Diapeutic") side, requiring (18)FDG detection of metastatic lesions, functional imaging of a protein target (e.g. Fatty Acid Synthase) using (11)C acetate, then a PET (or other)-imageable nanoparticle to demonstrate EPR accumulation, and then the administration of the pure-drug nanoparticle taken in by the most aggressive cancer cells in the perivascular space, as they would their "food".

Authors
Needham, D; Arslanagic, A; Glud, K; Hervella, P; Karimi, L; Høeilund-Carlsen, P-F; Kinoshita, K; Mollenhauer, J; Parra, E; Utoft, A; Walke, P
MLA Citation
Needham, D, Arslanagic, A, Glud, K, Hervella, P, Karimi, L, Høeilund-Carlsen, P-F, Kinoshita, K, Mollenhauer, J, Parra, E, Utoft, A, and Walke, P. "Bottom up design of nanoparticles for anti-cancer diapeutics: "put the drug in the cancer's food"." Journal of drug targeting 24.9 (November 2016): 836-856.
PMID
27646195
Source
epmc
Published In
Journal of Drug Targeting (Informa)
Volume
24
Issue
9
Publish Date
2016
Start Page
836
End Page
856

Inhibition of cholesterol transport in an intestine cell model by pine-derived phytosterols

Authors
Yi, J; Knudsen, TA; Nielsen, A-L; Duelund, L; Christensen, M; Hervella, P; Needham, D; Mouritsen, OG
MLA Citation
Yi, J, Knudsen, TA, Nielsen, A-L, Duelund, L, Christensen, M, Hervella, P, Needham, D, and Mouritsen, OG. "Inhibition of cholesterol transport in an intestine cell model by pine-derived phytosterols." Chemistry and Physics of Lipids 200 (October 2016): 62-73.
Source
crossref
Published In
Chemistry and Physics of Lipids
Volume
200
Publish Date
2016
Start Page
62
End Page
73
DOI
10.1016/j.chemphyslip.2016.06.008

A micropipette technique study of natural and synthetic lung surfactants at the air-water interface: The presence of a SP-B analog peptide promotes membrane aggregation, formation of tightly stacked lamellae and growth of myelin figures.

The present study is a microscopic interfacial characterization of a series of lung surfactant materials performed with the micropipette technique. The advantages of this technique include the measurement of equilibrium and dynamic surface tensions while acquiring structural and dynamic information at microscopic air-water interfaces in real time and upon compression. Here, we characterized a series of animal-derived and synthetic lung surfactant formulations, including native surfactant obtained from porcine lungs (NS); the commercial Curosurf, Infasurf and Survanta; and a synthetic Super Mini-B (SMB)-containing formulation. It was observed that the presence of the natural hydrophobic proteins and, more strikingly, the peptide SMB, promoted vesicle condensation as thick membrane stacks beneath the interface. Only in the presence of SMB, these stacks underwent spontaneous structural transformations, consisting of the nucleation and growth of microtubes and in some cases their subsequent coiling into helices. The dimensions of these tubes (2-15 μm diameter) and their linear (2-3 μm/s) and volumetric growth rates (20-30 μm(3)/s) were quantified, and no specific effects were found on them for increasing SMB concentrations from 0.1 to 4%. Nevertheless, a direct correlation between the number of tubes and SMB contents was found, suggesting that SMB molecules are the promoters of tube nucleation in these membranes. A detailed analysis of the tube formation process was performed following previous models for the growth of myelin figures, proposing a combined mechanism between dehydration-rehydration of the lipid bilayers and induction of mechanical defects by SMB that would act as nucleation sites for the tubes. The formation of tubes was also observed in Infasurf, and in NS only after subsequent expansion and compression, but neither in the other clinical surfactants nor in protein-free preparations. Finally, the connection between this data and the observations from the lung surfactant literature concerning the widely reported "near-zero surface tension" for lung surfactant films and intact alveolar surfaces is also discussed.

Authors
Parra, E; Kinoshita, K; Needham, D
MLA Citation
Parra, E, Kinoshita, K, and Needham, D. "A micropipette technique study of natural and synthetic lung surfactants at the air-water interface: The presence of a SP-B analog peptide promotes membrane aggregation, formation of tightly stacked lamellae and growth of myelin figures." Langmuir : the ACS journal of surfaces and colloids (September 21, 2016).
PMID
27653452
Source
epmc
Published In
Langmuir
Publish Date
2016

Encapsulation and retention of chelated-copper inside hydrophobic nanoparticles: Liquid cored nanoparticles show better retention than a solid core formulation

Authors
Hervella, P; Parra, E; Needham, D
MLA Citation
Hervella, P, Parra, E, and Needham, D. "Encapsulation and retention of chelated-copper inside hydrophobic nanoparticles: Liquid cored nanoparticles show better retention than a solid core formulation." European Journal of Pharmaceutics and Biopharmaceutics 102 (May 2016): 64-76.
Source
crossref
Published In
European Journal of Pharmaceutics and Biopharmaceutics
Volume
102
Publish Date
2016
Start Page
64
End Page
76
DOI
10.1016/j.ejpb.2016.02.015

Enzyme dehydration using Microglassification™ preserves the protein's structure and function.

Controlled enzyme dehydration using a new processing technique of Microglassification™ has been investigated. Aqueous solution microdroplets of lysozyme, α-chymotrypsin, catalase, and horseradish peroxidase were dehydrated in n-pentanol, n-octanol, n-decanol, triacetin, or butyl lactate, and changes in their structure and function were analyzed upon rehydration. Water solubility and microdroplet dissolution rate in each solvent decreased in the order: butyl lactate > n-pentanol > triacetin > n-octanol > n-decanol. Enzymes Microglassified™ in n-pentanol retained higher activity (93%-98%) than n-octanol (78%-85%) or n-decanol (75%-89%), whereas those Microglassified™ in triacetin (36%-75%) and butyl lactate (48%-79%) retained markedly lower activity. FTIR spectroscopy analyses showed α-helix to β-sheet transformation for all enzymes upon Microglassification™, reflecting a loss of bound water in the dried state; however, the enzymes reverted to native-like conformation upon rehydration. Accelerated stressed-storage tests using Microglassified™ lysozyme showed a significant (p < 0.01) decrease in enzymatic activity from 46,560 ± 2736 to 31,060 ± 4327 units/mg after 3 months of incubation; however, it was comparable to the activity of the lyophilized formulation throughout the test period. These results establish Microglassification™ as a viable technique for enzyme preservation without affecting its structure or function.

Authors
Aniket, ; Gaul, DA; Bitterfield, DL; Su, JT; Li, VM; Singh, I; Morton, J; Needham, D
MLA Citation
Aniket, , Gaul, DA, Bitterfield, DL, Su, JT, Li, VM, Singh, I, Morton, J, and Needham, D. "Enzyme dehydration using Microglassification™ preserves the protein's structure and function." Journal of pharmaceutical sciences 104.2 (February 2015): 640-651.
PMID
25557848
Source
epmc
Published In
Journal of Pharmaceutical Sciences
Volume
104
Issue
2
Publish Date
2015
Start Page
640
End Page
651
DOI
10.1002/jps.24279

Two phase I dose-escalation/pharmacokinetics studies of low temperature liposomal doxorubicin (LTLD) and mild local hyperthermia in heavily pretreated patients with local regionally recurrent breast cancer.

Unresectable chest wall recurrences of breast cancer (CWR) in heavily pretreated patients are especially difficult to treat. We hypothesised that thermally enhanced drug delivery using low temperature liposomal doxorubicin (LTLD), given with mild local hyperthermia (MLHT), will be safe and effective in this population.This paper combines the results of two similarly designed phase I trials. Eligible CWR patients had progressed on the chest wall after prior hormone therapy, chemotherapy, and radiotherapy. Patients were to get six cycles of LTLD every 21-35 days, followed immediately by chest wall MLHT for 1 hour at 40-42 °C. In the first trial 18 subjects received LTLD at 20, 30, or 40 mg/m2; in the second trial, 11 subjects received LTLD at 40 or 50 mg/m2.The median age of all 29 patients enrolled was 57 years. Thirteen patients (45%) had distant metastases on enrolment. Patients had received a median dose of 256 mg/m2 of prior anthracyclines and a median dose of 61 Gy of prior radiation. The median number of study treatments that subjects completed was four. The maximum tolerated dose was 50 mg/m2, with seven subjects (24%) developing reversible grade 3-4 neutropenia and four (14%) reversible grade 3-4 leucopenia. The rate of overall local response was 48% (14/29, 95% CI: 30-66%), with. five patients (17%) achieving complete local responses and nine patients (31%) having partial local responses.LTLD at 50 mg/m2 and MLHT is safe. This combined therapy produces objective responses in heavily pretreated CWR patients. Future work should test thermally enhanced LTLD delivery in a less advanced patient population.

Authors
Zagar, TM; Vujaskovic, Z; Formenti, S; Rugo, H; Muggia, F; O'Connor, B; Myerson, R; Stauffer, P; Hsu, I-C; Diederich, C; Straube, W; Boss, M-K; Boico, A; Craciunescu, O; Maccarini, P; Needham, D; Borys, N; Blackwell, KL; Dewhirst, MW
MLA Citation
Zagar, TM, Vujaskovic, Z, Formenti, S, Rugo, H, Muggia, F, O'Connor, B, Myerson, R, Stauffer, P, Hsu, I-C, Diederich, C, Straube, W, Boss, M-K, Boico, A, Craciunescu, O, Maccarini, P, Needham, D, Borys, N, Blackwell, KL, and Dewhirst, MW. "Two phase I dose-escalation/pharmacokinetics studies of low temperature liposomal doxorubicin (LTLD) and mild local hyperthermia in heavily pretreated patients with local regionally recurrent breast cancer." International journal of hyperthermia : the official journal of European Society for Hyperthermic Oncology, North American Hyperthermia Group 30.5 (August 2014): 285-294.
PMID
25144817
Source
epmc
Published In
International Journal of Hyperthermia (Informa)
Volume
30
Issue
5
Publish Date
2014
Start Page
285
End Page
294
DOI
10.3109/02656736.2014.936049

Quantitative optical microscopy and micromanipulation studies on the lipid bilayer membranes of giant unilamellar vesicles.

This manuscript discusses basic methodological aspects of optical microscopy and micromanipulation methods to study membranes and reviews methods to generate giant unilamellar vesicles (GUVs). In particular, we focus on the use of fluorescence microscopy and micropipet manipulation techniques to study composition-structure-property materials relationships of free-standing lipid bilayer membranes. Because their size (∼5-100 μm diameter) that is well above the resolution limit of regular light microscopes, GUVs are suitable membrane models for optical microscopy and micromanipulation experimentation. For instance, using different fluorescent reporters, fluorescence microscopy allows strategies to study membrane lateral structure/dynamics at the level of single vesicles of diverse compositions. The micropipet manipulation technique on the other hand, uses Hoffman modulation contrast microscopy and allows studies on the mechanical, thermal, molecular exchange and adhesive-interactive properties of compositionally different membranes under controlled environmental conditions. The goal of this review is to (i) provide a historical perspective for both techniques; (ii) present and discuss some of their most important contributions to our understanding of lipid bilayer membranes; and (iii) outline studies that would utilize both techniques simultaneously on the same vesicle thus bringing the ability to characterize structure and strain responses together with the direct application of well-defined stresses to a single membrane or observe the effects of adhesive spreading. Knowledge gained by these studies has informed several applications of lipid membranes including their use as lung surfactants and drug delivery systems for cancer.

Authors
Bagatolli, LA; Needham, D
MLA Citation
Bagatolli, LA, and Needham, D. "Quantitative optical microscopy and micromanipulation studies on the lipid bilayer membranes of giant unilamellar vesicles." Chemistry and physics of lipids 181 (July 2014): 99-120.
PMID
24632023
Source
epmc
Published In
Chemistry and Physics of Lipids
Volume
181
Publish Date
2014
Start Page
99
End Page
120
DOI
10.1016/j.chemphyslip.2014.02.009

MicroglassificationTM: A novel technique for protein dehydration

The dehydration of biologics is commonly employed to achieve solid-dose formulation and enhanced stability during long-term preservation. We have developed a novel process, MicroglassificationTM, which can rapidly and controllably dehydrate protein solutions into solid amorphous microspheres at room temperature. Single bovine serum albumin (BSA) microdroplets were suspended in pentanol or decanol using a micropipette, and the dynamic changes in droplet dissolution were observed in real-time and correlated to protein's water of hydration, medium's water activity, and microsphere protein concentration. MicroglassificationTM was also carried out at bulk scale, and changes in BSA secondary structure were analyzed by Fourier transform infrared spectroscopy and fluorescence spectroscopy; multimer formation was detected by native gel electrophoresis. BSA concentration in the microsphere increased with solvent exposure time and decreasing water activity. Image analysis at single particle and bulk scale showed the formation of solid BSA microspheres with a maximum protein concentration of 1147 ± 32 mg/mL. The native BSA samples were dehydrated to approximately 450 waters per BSA, which is well below monolayer coverage of 1282 waters per BSA. The secondary structure of MicroglassifiedTM BSA reverted to native-like conformation upon rehydration with only minor irreversible aggregation (2.7%). Results of the study establish the efficacy of the MicroglassificationTM for the successful dehydration of biologics. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

Authors
Aniket, ; Gaul, DA; Rickard, DL; Needham, D
MLA Citation
Aniket, , Gaul, DA, Rickard, DL, and Needham, D. "MicroglassificationTM: A novel technique for protein dehydration." Journal of Pharmaceutical Sciences 103.3 (March 1, 2014): 810-819.
Source
scopus
Published In
Journal of Pharmaceutical Sciences
Volume
103
Issue
3
Publish Date
2014
Start Page
810
End Page
819
DOI
10.1002/jps.23847

Microglassification™: a novel technique for protein dehydration.

The dehydration of biologics is commonly employed to achieve solid-dose formulation and enhanced stability during long-term preservation. We have developed a novel process, Microglassification™, which can rapidly and controllably dehydrate protein solutions into solid amorphous microspheres at room temperature. Single bovine serum albumin (BSA) microdroplets were suspended in pentanol or decanol using a micropipette, and the dynamic changes in droplet dissolution were observed in real-time and correlated to protein's water of hydration, medium's water activity, and microsphere protein concentration. Microglassification™ was also carried out at bulk scale, and changes in BSA secondary structure were analyzed by Fourier transform infrared spectroscopy and fluorescence spectroscopy; multimer formation was detected by native gel electrophoresis. BSA concentration in the microsphere increased with solvent exposure time and decreasing water activity. Image analysis at single particle and bulk scale showed the formation of solid BSA microspheres with a maximum protein concentration of 1147 ± 32 mg/mL. The native BSA samples were dehydrated to approximately 450 waters per BSA, which is well below monolayer coverage of 1282 waters per BSA. The secondary structure of Microglassified™ BSA reverted to native-like conformation upon rehydration with only minor irreversible aggregation (2.7%). Results of the study establish the efficacy of the Microglassification™ for the successful dehydration of biologics.

Authors
Aniket, ; Gaul, DA; Rickard, DL; Needham, D
MLA Citation
Aniket, , Gaul, DA, Rickard, DL, and Needham, D. "Microglassification™: a novel technique for protein dehydration." J Pharm Sci 103.3 (March 2014): 810-820.
PMID
24415208
Source
pubmed
Published In
Journal of Pharmaceutical Sciences
Volume
103
Issue
3
Publish Date
2014
Start Page
810
End Page
820
DOI
10.1002/jps.23847

Quantitative optical microscopy and micromanipulation studies on the lipid bilayer membranes of giant unilamellar vesicles

This manuscript discusses basic methodological aspects of optical microscopy and micromanipulation methods to study membranes and reviews methods to generate giant unilamellar vesicles (GUVs). In particular, we focus on the use of fluorescence microscopy and micropipet manipulation techniques to study composition-structure-property materials relationships of free-standing lipid bilayer membranes. Because their size (∼5-100 μm diameter) that is well above the resolution limit of regular light microscopes, GUVs are suitable membrane models for optical microscopy and micromanipulation experimentation. For instance, using different fluorescent reporters, fluorescence microscopy allows strategies to study membrane lateral structure/dynamics at the level of single vesicles of diverse compositions. The micropipet manipulation technique on the other hand, uses Hoffman modulation contrast microscopy and allows studies on the mechanical, thermal, molecular exchange and adhesive-interactive properties of compositionally different membranes under controlled environmental conditions. The goal of this review is to (i) provide a historical perspective for both techniques; (ii) present and discuss some of their most important contributions to our understanding of lipid bilayer membranes; and (iii) outline studies that would utilize both techniques simultaneously on the same vesicle thus bringing the ability to characterize structure and strain responses together with the direct application of well-defined stresses to a single membrane or observe the effects of adhesive spreading. Knowledge gained by these studies has informed several applications of lipid membranes including their use as lung surfactants and drug delivery systems for cancer. © 2014 Elsevier Ireland Ltd.

Authors
Bagatolli, LA; Needham, D
MLA Citation
Bagatolli, LA, and Needham, D. "Quantitative optical microscopy and micromanipulation studies on the lipid bilayer membranes of giant unilamellar vesicles." Chemistry and Physics of Lipids 181 (January 1, 2014): 99-120.
Source
scopus
Published In
Chemistry and Physics of Lipids
Volume
181
Publish Date
2014
Start Page
99
End Page
120
DOI
10.1016/j.chemphyslip.2014.02.009

Novel radioisotope-based nanomedical approaches

Radioisotope therapy of cancer is on the rise applying mainly β-emitting radionuclides. However, due to exposure of healthy tissues, the maximum achievable radiation dose with these is limited. Auger-electron emitters (AEs) represent a promising alternative because of their mode of decay within a short nanometer range. The challenge is that their therapeutic efficacy relies on a close vicinity to DNA. To overcome this and to minimize toxicity, the construction of smart nanomedical devices is required, which ascertain tumor cell targeting with succeeding cellular uptake and nuclear translocation. In this review we describe the potential of AEs with focus on their delivery down to the DNA level and their cellular effects. Reported efforts comprise different tumor-targeting strategies, including the use of antibodies or peptides with nuclear localizing sequences. Recently, attention has shifted to various nanoparticle formats for overcoming delivery problems. To this end, these approaches have mostly been tested in cell lines in vitro applying AEs more suited for imaging than therapy. This defines a demand for nanomedical formulations with documented in vivo activity, using AEs selected for their therapeutic potential to come closer to real clinical settings. © 2013 by Walter de Gruyter Berlin Boston.

Authors
Olsen, BB; Thisgaard, H; Vogel, S; Thomassen, M; Kruse, TA; Needham, D; Mollenhauer, J; Flemming Høilund-Carlsen, P
MLA Citation
Olsen, BB, Thisgaard, H, Vogel, S, Thomassen, M, Kruse, TA, Needham, D, Mollenhauer, J, and Flemming Høilund-Carlsen, P. "Novel radioisotope-based nanomedical approaches." European Journal of Nanomedicine 5.4 (December 1, 2013): 181-193. (Review)
Source
scopus
Published In
European Journal of Nanomedicine
Volume
5
Issue
4
Publish Date
2013
Start Page
181
End Page
193
DOI
10.1515/ejnm-2013-0025

Materials science and engineering of the low temperature sensitive liposome (LTSL): Composition-structure-property relationships that underlie its design and performance

Authors
Needham, D; Dewhirst, MW
MLA Citation
Needham, D, and Dewhirst, MW. "Materials science and engineering of the low temperature sensitive liposome (LTSL): Composition-structure-property relationships that underlie its design and performance." RSC Smart Materials 1.1 (November 25, 2013): 33-79.
Source
scopus
Published In
RSC Smart Materials
Volume
1
Issue
1
Publish Date
2013
Start Page
33
End Page
79

Mass transfer in the dissolution of a multicomponent liquid droplet in an immiscible liquid environment.

The Epstein-Plesset equation has recently been shown to predict accurately the dissolution of a pure liquid microdroplet into a second immiscible solvent, such as oil into water. Here, we present a series of new experiments and a modification to this equation to model the dissolution of a two-component oil-mixture microdroplet into a second immiscible solvent in which the two materials of the droplet have different solubilities. The model is based on a reduced surface area approximation and the assumption of ideal homogeneous mixing [mass flux d(m(i))/dt = A(frac(i))D(i)(c(i) - c(s)){(1/R) + (1/(πD(i)t)(1/2)}] where A(frac(i)) is the area fraction of component i, c(i) and c(s) are the initial and saturation concentrations of the droplet material in the surrounding medium, R is the radius of the droplet, t is time, and D(i) is the coefficient of diffusion of component i in the surrounding medium. This new model has been tested by the use of a two-chamber micropipet-based method, which measured the dissolution of single individual microdroplets of mutually miscible liquid mixtures (ethyl acetate/butyl acetate and butyl acetate/amyl acetate) in water. We additionally measured the diffusion coefficient of the pure materials-ethyl acetate, butyl acetate, and amyl acetate-in water at 22 °C. Diffusion coefficients for the pure acetates in water were 8.65 × 10(-6), 7.61 × 10(-6), and 9.14 × 10(-6) cm(2)/s, respectively. This model accurately predicts the dissolution of microdroplets for the ethyl acetate/butyl acetate and butyl acetate/amyl acetate systems given the solubility and diffusion coefficients of each of the individual components in water as well as the initial droplet radius. The average mean squared error was 8.96%. The dissolution of a spherical ideally mixed multicomponent droplet closely follows the modified Epstein-Plesset model presented here.

Authors
Su, JT; Needham, D
MLA Citation
Su, JT, and Needham, D. "Mass transfer in the dissolution of a multicomponent liquid droplet in an immiscible liquid environment." Langmuir 29.44 (November 5, 2013): 13339-13345.
PMID
24050124
Source
pubmed
Published In
Langmuir
Volume
29
Issue
44
Publish Date
2013
Start Page
13339
End Page
13345
DOI
10.1021/la402533j

Reverse engineering of the low temperature-sensitive liposome (LTSL) for treating cancer

This chapter is as much about the process of reverse engineering as it is about a particular drug delivery system. It presents the materials science and materials engineering concepts that went into the design and testing of the LTSL including: the roles of each of the components that make up the composite membrane; how the molecular and nanostructures that they form might influence the already anomalous permeability at the phase transition of the bilayer; and how this thermally sensitive drug delivery system leads to ultrafast, heat-mediated, triggered, intravascular release of pre-loaded doxorubicin. Release of drug penetrating deep into the tumor interstitium, is controlled by where, when, and for how long mild hyperthermia (HT) is applied. 1 in relation to the liposome administration. This formulation, as ThermoDox®, has been used in a completed 700 patient Phase III human clinical trial in liver cancer (HEAT study), is in a Phase II trial in chest wall recurrence of cancer (DIGNITY study), and is also in a Phase I trial of patients with colorectal liver metastases (ABLATE study).2 It is a bench-to-bedside story that addresses both overcoming limitations in nanoparticle drug delivery and also the importance of research implementation in translation to the clinic. With additional research and preclinical studies underway, including exploring the use of high frequency ultrasound (HiFu) as a heating modality, and a range of other drugs, imaging agents and biological modifiers poised for encapsulation, the LTSL could provide a new paradigm for drug and agent delivery for the treatment of localized tumors - '. rapid triggered drug release in the tumor bloodstream and deep penetration of drug into the tumor tissue'. Unfortunately, the Phase III trial in liver cancer failed to meet its required endpoints for progressionfree survival (PFS). While data is still being analyzed, preclinical and now clinical research shows that it is essential for all future trials of this particular formulation, that the whole tumor should be heated to the desired temperature (41-42°C), and maintained at that temperature while ThermoDox® is infused for a minimum of 20 min, and probably an hour, i.e., heat first and then infuse drug. © 2013 Woodhead Publishing Limited. All rights reserved.

Authors
Needham, D
MLA Citation
Needham, D. "Reverse engineering of the low temperature-sensitive liposome (LTSL) for treating cancer." Biomaterials for Cancer Therapeutics: Diagnosis, Prevention and Therapy. October 1, 2013. 270-348.
Source
scopus
Publish Date
2013
Start Page
270
End Page
348
DOI
10.1533/9780857096760.3.270

A method to convert MRI images of temperature change into images of absolute temperature in solid tumours.

PURPOSE: During hyperthermia (HT), the therapeutic response of tumours varies substantially within the target temperature range (39-43 °C). Current thermometry methods are either invasive or measure only temperature change, which limits the ability to study tissue responses to HT. This study combines manganese-containing low temperature sensitive liposomes (Mn-LTSL) with proton resonance frequency shift (PRFS) thermometry to measure absolute temperature in tumours with high spatial and temporal resolution using MRI. METHODS: Liposomes were loaded with 300 mM MnSO(4). The phase transition temperature (T(m)) of Mn-LTSL samples was measured by differential scanning calorimetry (DSC). The release of manganese from Mn-LTSL in saline was characterised with inductively coupled plasma atomic emission spectroscopy. A 2T GE small animal scanner was used to acquire dynamic T1-weighted images and temperature change images of Mn-LTSL in saline phantoms and fibrosarcoma-bearing Fisher-344 rats receiving hyperthermia after Mn-LTSL injection. RESULTS: The T(m) of Mn-LTSL in rat blood was 42.9 ± 0.2 °C (DSC). For Mn-LTSL samples (0.06 mM-0.5 mM Mn(2+) in saline) heated monotonically from 30 °C to 50 °C, a peak in the rate of MRI signal enhancement occurred at 43.1° ± 0.3 °C. The same peak in signal enhancement rate was observed during heating of fibrosarcoma tumours (N = 3) after injection of Mn-LTSL, and the peak was used to convert temperature change images into absolute temperature. Accuracies of calibrated temperature measurements were in the range 0.9-1.8 °C. CONCLUSION: The release of Mn(2+) from Mn-LTSL affects the rate of MR signal enhancement which enables conversion of MRI-based temperature change images to absolute temperature.

Authors
Davis, RM; Viglianti, BL; Yarmolenko, P; Park, J-Y; Stauffer, P; Needham, D; Dewhirst, MW
MLA Citation
Davis, RM, Viglianti, BL, Yarmolenko, P, Park, J-Y, Stauffer, P, Needham, D, and Dewhirst, MW. "A method to convert MRI images of temperature change into images of absolute temperature in solid tumours." Int J Hyperthermia 29.6 (September 2013): 569-581.
PMID
23957326
Source
pubmed
Published In
International Journal of Hyperthermia (Informa)
Volume
29
Issue
6
Publish Date
2013
Start Page
569
End Page
581
DOI
10.3109/02656736.2013.790091

Materials characterization of the low temperature sensitive liposome (LTSL): effects of the lipid composition (lysolipid and DSPE-PEG2000) on the thermal transition and release of doxorubicin

Authors
Needham, D; Park, J-Y; Wright, AM; Tong, J
MLA Citation
Needham, D, Park, J-Y, Wright, AM, and Tong, J. "Materials characterization of the low temperature sensitive liposome (LTSL): effects of the lipid composition (lysolipid and DSPE-PEG2000) on the thermal transition and release of doxorubicin." FARADAY DISCUSSIONS 161 (2013): 515-534.
PMID
23805756
Source
wos-lite
Published In
Faraday Discussions
Volume
161
Publish Date
2013
Start Page
515
End Page
534
DOI
10.1039/c2fd20111a

Overcoming limitations in nanoparticle drug delivery: triggered, intravascular release to improve drug penetration into tumors.

Traditionally, the goal of nanoparticle-based chemotherapy has been to decrease normal tissue toxicity by improving drug specificity to tumors. The enhanced permeability and retention effect can permit passive accumulation into tumor interstitium. However, suboptimal delivery is achieved with most nanoparticles because of heterogeneities of vascular permeability, which limits nanoparticle penetration. Furthermore, slow drug release limits bioavailability. We developed a fast drug-releasing liposome triggered by local heat that has already shown substantial antitumor efficacy and is in human trials. Here, we show that thermally sensitive liposomes (Dox-TSL) release doxorubicin inside the tumor vasculature. Real-time confocal imaging of doxorubicin delivery to murine tumors in window chambers and histologic analysis of flank tumors illustrates that intravascular drug release increases free drug in the interstitial space. This increases both the time that tumor cells are exposed to maximum drug levels and the drug penetration distance, compared with free drug or traditional pegylated liposomes. These improvements in drug bioavailability establish a new paradigm in drug delivery: rapidly triggered drug release in the tumor bloodstream.

Authors
Manzoor, AA; Lindner, LH; Landon, CD; Park, J-Y; Simnick, AJ; Dreher, MR; Das, S; Hanna, G; Park, W; Chilkoti, A; Koning, GA; ten Hagen, TLM; Needham, D; Dewhirst, MW
MLA Citation
Manzoor, AA, Lindner, LH, Landon, CD, Park, J-Y, Simnick, AJ, Dreher, MR, Das, S, Hanna, G, Park, W, Chilkoti, A, Koning, GA, ten Hagen, TLM, Needham, D, and Dewhirst, MW. "Overcoming limitations in nanoparticle drug delivery: triggered, intravascular release to improve drug penetration into tumors." Cancer Res 72.21 (November 1, 2012): 5566-5575.
PMID
22952218
Source
pubmed
Published In
Cancer Research
Volume
72
Issue
21
Publish Date
2012
Start Page
5566
End Page
5575
DOI
10.1158/0008-5472.CAN-12-1683

Phase separation behavior of fusidic acid and rifampicin in PLGA microspheres

The purpose of this study was to characterize the phase separation behavior of fusidic acid (FA) and rifampicin (RIF) in poly(d,l-lactic acid-co-glycolic acid) (PLGA) using a model microsphere formulation. To accomplish this, microspheres containing 20% FA with 0%, 5%, 10%, 20%, and 30% RIF and 20% RIF with 30%, 20% 10%, 5%, and 0% FA were prepared by solvent evaporation. Drug-polymer and drug-drug compatibility and miscibility were characterized using laser confocal microscopy, Raman spectroscopy, XRPD, DSC, and real-time video recordings of single-microsphere formation. The encapsulation of FA and RIF alone, or in combination, results in a liquid-liquid phase separation of solvent-and-drug-rich microdomains that are excluded from the polymer bulk during microsphere hardening, resulting in amorphous spherical drug-rich domains within the polymer bulk and on the microsphere surface. FA and RIF phase separate from PLGA at relative droplet volumes of 0.311 ± 0.014 and 0.194 ± 0.000, respectively, predictive of the incompatibility of each drug and PLGA. When coloaded, FA and RIF phase separate in a single event at the relative droplet volume 0.251 ± 0.002, intermediate between each of the monoloaded formulations and dependent on the relative contribution of FA or RIF. The release of FA and RIF from phase-separated microspheres was characterized exclusively by a burst release and was dependent on the phase exclusion of surface drug-rich domains. Phase separation results in coalescence of drug-rich microdroplets and polymer phase exclusion, and it is dependent on the compatibility between FA and RIF and PLGA. FA and RIF are mutually miscible in all proportions as an amorphous glass, and they phase separate from the polymer as such. These drug-rich domains were excluded to the surface of the microspheres, and subsequent release of both drugs from the microspheres was rapid and reflected this surface location. © 2012 American Chemical Society.

Authors
Gilchrist, SE; Rickard, DL; Letchford, K; Needham, D; Burt, HM
MLA Citation
Gilchrist, SE, Rickard, DL, Letchford, K, Needham, D, and Burt, HM. "Phase separation behavior of fusidic acid and rifampicin in PLGA microspheres." Molecular Pharmaceutics 9.5 (2012): 1489-1501.
PMID
22482935
Source
scival
Published In
Molecular Pharmaceutics
Volume
9
Issue
5
Publish Date
2012
Start Page
1489
End Page
1501
DOI
10.1021/mp300099f

Lipid structures: a brief history of multisomes.

Authors
Needham, D
MLA Citation
Needham, D. "Lipid structures: a brief history of multisomes. (Published online)" Nat Nanotechnol 6.12 (December 6, 2011): 761-762.
PMID
22146543
Source
pubmed
Published In
Nature Nanotechnology
Volume
6
Issue
12
Publish Date
2011
Start Page
761
End Page
762
DOI
10.1038/nnano.2011.218

Nanoscale drug delivery and hyperthermia: The materials design and preclinical and clinical testing of low temperature-sensitive liposomes used in combination with mild hyperthermia in the treatment of local cancer

The overall objective of liposomal drug delivery is to selectively target drug delivery to diseased tissue, while minimizing drug delivery to critical normal tissues. The purpose of this review is to provide an overview of temperaturesensitive liposomes in general and the Low Temperature-Sensitive Liposome (LTSL) in particular. We give a brief description of the material design of LTSL and highlight the likely mechanism behind temperature-triggered drug release. A complete review of the progress and results of the latest preclinical and clinical studies that demonstrate enhanced drug delivery with the combined treatment of hyperthermia and liposomes is provided as well as a clinical perspective on cancers that would benefit from hyperthermia as an adjuvant treatment for temperature-triggered chemotherapeutics. This review discusses the ideas, goals, and processes behind temperature-sensitive liposome development in the laboratory to the current use in preclinical and clinical settings.

Authors
Landon, CD; Park, J-Y; Needham, D; Dewhirst, MW
MLA Citation
Landon, CD, Park, J-Y, Needham, D, and Dewhirst, MW. "Nanoscale drug delivery and hyperthermia: The materials design and preclinical and clinical testing of low temperature-sensitive liposomes used in combination with mild hyperthermia in the treatment of local cancer." Open Nanomedicine Journal 3.SPEC. ISSUE (2011): 38-64.
PMID
23807899
Source
scival
Published In
Open Nanomedicine Journal
Volume
3
Issue
SPEC. ISSUE
Publish Date
2011
Start Page
38
End Page
64

Hydration potential of lysozyme: protein dehydration using a single microparticle technique.

For biological molecules in aqueous solution, the hydration pressure as a function of distance from the molecular surface represents a very short-range repulsive pressure that limits atom-atom contact, opposing the attractive van der Waals pressure. Whereas the separation distance for molecules that easily arrange into ordered arrays (e.g., lipids, DNA, collagen fibers) can be determined from x-ray diffraction, many globular proteins are not as easily structured. Using a new micropipette technique, spherical, glassified protein microbeads can be made that allow determination of protein hydration as a function of the water activity (a(w)) in a surrounding medium (decanol). By adjusting a(w) of the dehydration medium, the final protein concentration of the solid microbead is controlled, and ranges from 700 to 1150 mg/mL. By controlling a(w) (and thus the osmotic pressure) around lysozyme, the repulsive pressure was determined as a function of distance between each globular, ellipsoid protein. For separation distances, d, between 2.5 and 9 A, the repulsive decay length was 1.7 A and the pressure extrapolated to d = 0 was 2.2 x 10(8) N/m(2), indicating that the hydration pressure for lysozyme is similar to other biological interfaces such as phospholipid bilayers.

Authors
Rickard, DL; Duncan, PB; Needham, D
MLA Citation
Rickard, DL, Duncan, PB, and Needham, D. "Hydration potential of lysozyme: protein dehydration using a single microparticle technique." Biophys J 98.6 (March 17, 2010): 1075-1084.
PMID
20303865
Source
pubmed
Published In
Biophysical Journal
Volume
98
Issue
6
Publish Date
2010
Start Page
1075
End Page
1084
DOI
10.1016/j.bpj.2009.11.043

The effect of hydrogen bonding on the diffusion of water in n-alkanes and n-alcohols measured with a novel single microdroplet method.

While the Stokes-Einstein (SE) equation predicts that the diffusion coefficient of a solute will be inversely proportional to the viscosity of the solvent, this relation is commonly known to fail for solutes, which are the same size or smaller than the solvent. Multiple researchers have reported that for small solutes, the diffusion coefficient is inversely proportional to the viscosity to a fractional power, and that solutes actually diffuse faster than SE predicts. For other solvent systems, attractive solute-solvent interactions, such as hydrogen bonding, are known to retard the diffusion of a solute. Some researchers have interpreted the slower diffusion due to hydrogen bonding as resulting from the effective diffusion of a larger complex of a solute and solvent molecules. We have developed and used a novel micropipette technique, which can form and hold a single microdroplet of water while it dissolves in a diffusion controlled environment into the solvent. This method has been used to examine the diffusion of water in both n-alkanes and n-alcohols. It was found that the polar solute water, diffusing in a solvent with which it cannot hydrogen bond, closely resembles small nonpolar solutes such as xenon and krypton diffusing in n-alkanes, with diffusion coefficients ranging from 12.5x10(-5) cm(2)/s for water in n-pentane to 1.15x10(-5) cm(2)/s for water in hexadecane. Diffusion coefficients were found to be inversely proportional to viscosity to a fractional power, and diffusion coefficients were faster than SE predicts. For water diffusing in a solvent (n-alcohols) with which it can hydrogen bond, diffusion coefficient values ranged from 1.75x10(-5) cm(2)/s in n-methanol to 0.364x10(-5) cm(2)/s in n-octanol, and diffusion was slower than an alkane of corresponding viscosity. We find no evidence for solute-solvent complex diffusion. Rather, it is possible that the small solute water may be retarded by relatively longer residence times (compared to non-H-bonding solvents) as it moves through the liquid.

Authors
Su, JT; Duncan, PB; Momaya, A; Jutila, A; Needham, D
MLA Citation
Su, JT, Duncan, PB, Momaya, A, Jutila, A, and Needham, D. "The effect of hydrogen bonding on the diffusion of water in n-alkanes and n-alcohols measured with a novel single microdroplet method." J Chem Phys 132.4 (January 28, 2010): 044506-.
Website
http://hdl.handle.net/10161/3317
PMID
20113048
Source
pubmed
Published In
Journal of Chemical Physics
Volume
132
Issue
4
Publish Date
2010
Start Page
044506
DOI
10.1063/1.3298857

Comparative effects of thermosensitive doxorubicin-containing liposomes and hyperthermia in human and murine tumours.

PURPOSE: In previous reports, laboratory-made lysolecithin-containing thermosensitive liposome encapsulating doxorubicin (LTSL-DOX) showed potent anticancer effects in FaDu human squamous cell carcinoma. To further study the spectrum of LTSL-DOX activity, the efficacy of its commercial formulation was re-examined in FaDu and compared in HCT116, PC3, SKOV-3 and 4T07 cancer cell lines. Factors that may influence differences in HT-LTSL-DOX efficacy were also examined. METHODS: Anticancer effect was measured using standard growth delay methods. We measured doubling time and clonogenic survival after doxorubicin exposure in vitro, and interstitial pH and drug concentrations in vivo. RESULTS: In all five tumour types, HT-LTSL-DOX increased median tumour growth time compared with untreated controls (p < 0.0006) and HT alone (p < 0.01), and compared with LTSL-DOX alone in FaDu, PC-3 and HCT-116 (p < 0.0006). HT-LTSL-DOX yielded significantly higher drug concentrations than LTSL-DOX (p < 0.0001). FaDu was most sensitive (p < 0.0014) to doxorubicin (IC(50) = 90 nM) in vitro, compared to the other cell lines (IC(50) = 129-168 nM). Of the parameters tested for correlation with efficacy, only the correlation of in vitro doubling time and in vivo median growth time was significant (Pearson r = 0.98, p = 0.0035). Slower-growing SKOV-3 and PC-3 had the greatest numbers of complete regressions and longest tumour growth delays, which are clinically important parameters. CONCLUSIONS: These results strongly suggest that variations in anti-tumour effect of HT-LTSL-DOX are primarily related to in vitro doubling time. In the clinic, the rate of tumour progression must be considered in design of treatment regimens involving HT-LTSL-DOX.

Authors
Yarmolenko, PS; Zhao, Y; Landon, C; Spasojevic, I; Yuan, F; Needham, D; Viglianti, BL; Dewhirst, MW
MLA Citation
Yarmolenko, PS, Zhao, Y, Landon, C, Spasojevic, I, Yuan, F, Needham, D, Viglianti, BL, and Dewhirst, MW. "Comparative effects of thermosensitive doxorubicin-containing liposomes and hyperthermia in human and murine tumours." Int J Hyperthermia 26.5 (2010): 485-498.
PMID
20597627
Source
pubmed
Published In
International Journal of Hyperthermia (Informa)
Volume
26
Issue
5
Publish Date
2010
Start Page
485
End Page
498
DOI
10.3109/02656731003789284

PLGA and PHBV microsphere formulations and solid-state characterization: Possible implications for local delivery of fusidic acid for the treatment and prevention of orthopaedic infections

Purpose: To develop and characterize the solid-state properties of poly(DL-lactic-co-glycolic acid) (PLGA) and poly(3-hydroxybutyric acid-co-3-hydroxyvaleric acid) (PHBV) microspheres for the localized and controlled release of fusidic acid (FA). Methods: The effects of FA loading and polymer composition on the mean diameter, encapsulation efficiency and FA released from the microspheres were determined. The solid-state and phase separation properties of the microspheres were characterized using DSC, XRPD, Raman spectroscopy, SEM, laser confocal and real time recording of single microspheres formation. Results: Above a loading of 1% (w/w) FA phase separated from PLGA polymer and formed distinct spherical FA-rich amorphous microdomains throughout the PLGA microsphere. For FA-loaded PLGA microspheres, encapsulation efficiency and cumulative release increased with initial drug loading. Similarly, cumulative release from FA-loaded PHBV microspheres was increased by FA loading. After the initial burst release, FA was released from PLGA microspheres much slower compared to PHBV microspheres. Conclusions: A unique phase separation phenomenon of FA in PLGA but not in PHBV polymers was observed, driven by coalescence of liquid microdroplets of a DCM-FA-rich phase in the forming microsphere. © 2009 Springer Science+Business Media, LLC.

Authors
Yang, C; Plackett, D; Needham, D; Burt, HM
MLA Citation
Yang, C, Plackett, D, Needham, D, and Burt, HM. "PLGA and PHBV microsphere formulations and solid-state characterization: Possible implications for local delivery of fusidic acid for the treatment and prevention of orthopaedic infections." Pharmaceutical Research 26.7 (2009): 1644-1656.
PMID
19384471
Source
scival
Published In
Pharmaceutical Research
Volume
26
Issue
7
Publish Date
2009
Start Page
1644
End Page
1656
DOI
10.1007/s11095-009-9875-5

Tumor microvascular permeability is a key determinant for antivascular effects of doxorubicin encapsulated in a temperature sensitive liposome.

Previous data have demonstrated that doxorubicin (DOX) released from a lysolecithin-containing thermosensitive liposome (LTSL) can shut down blood flow in a human tumor xenograft (FaDu) in mice when the treatment is combined with hyperthermia (HT), suggesting that LTSL-DOX is a potential antivascular agent. To further understand mechanisms of the treatment, we investigated effects of LTSL-DOX (5 mg/kg body weight) plus HT (42 degrees C, 1 h) on microcirculation in another tumor (a murine mammary carcinoma, 4T07) implanted in mouse dorsal skin-fold chambers and dose responses of tumor (FaDu and 4T07) and endothelial cells to LTSL-DOX or free DOX with or without HT. We observed that LTSL-DOXHT could significantly reduce blood flow and microvascular density in 4T07 tumors. The antivascular efficacy of LTSLDOX- HT could be enhanced through increasing tumor microvascular permeability of liposomes by using platelet activating factor (PAF). We also observed that the dose responses of FaDu and 4T07 to DOX in vitro were similar to each other and could be enhanced by HT. Taken together, these data suggested that tumor microvascular permeability was more critical than the sensitivity of tumor cells to DOX in determining the antivascular efficacy of LTSL-DOX-HT treatment.

Authors
Chen, Q; Krol, A; Wright, A; Needham, D; Dewhirst, MW; Yuan, F
MLA Citation
Chen, Q, Krol, A, Wright, A, Needham, D, Dewhirst, MW, and Yuan, F. "Tumor microvascular permeability is a key determinant for antivascular effects of doxorubicin encapsulated in a temperature sensitive liposome." Int J Hyperthermia 24.6 (September 2008): 475-482.
PMID
18608573
Source
pubmed
Published In
International Journal of Hyperthermia (Informa)
Volume
24
Issue
6
Publish Date
2008
Start Page
475
End Page
482
DOI
10.1080/02656730701854767

Rationale for and measurement of liposomal drug delivery with hyperthermia using non-invasive imaging techniques.

The purpose of this review is to present an overview of the state-of-the-art imaging modalities used to track drug delivery from liposomal formulations into tumors during or after hyperthermia treatment. Liposomes are a drug delivery system comprised of a phospholipid bilayer surrounding an aqueous core and have been shown to accumulate following hyperthermia therapy. Use of contrast-containing liposomes in conjunction with hyperthermia therapy holds great promise to be able to directly measure drug dose concentrations as well as to non-invasively describe patterns of drug distribution with MR and PET/SPECT imaging modalities. We will review the rationale for using this approach and the potential advantages of having such information available during and after treatment.

Authors
Tashjian, JA; Dewhirst, MW; Needham, D; Viglianti, BL
MLA Citation
Tashjian, JA, Dewhirst, MW, Needham, D, and Viglianti, BL. "Rationale for and measurement of liposomal drug delivery with hyperthermia using non-invasive imaging techniques." Int J Hyperthermia 24.1 (February 2008): 79-90. (Review)
PMID
18214771
Source
pubmed
Published In
International Journal of Hyperthermia (Informa)
Volume
24
Issue
1
Publish Date
2008
Start Page
79
End Page
90
DOI
10.1080/02656730701840147

Novel encapsulation of partially dehydrated protein microparticles in PLGA microspheres

Authors
Montalvo-Ortiz, BL; Sosa, B; Velez, D; Needham, D; Griebenow, K
MLA Citation
Montalvo-Ortiz, BL, Sosa, B, Velez, D, Needham, D, and Griebenow, K. "Novel encapsulation of partially dehydrated protein microparticles in PLGA microspheres." JOURNAL OF BIOTECHNOLOGY 131.2 (September 2007): S51-S52.
Source
wos-lite
Published In
Journal of Biotechnology
Volume
131
Issue
2
Publish Date
2007
Start Page
S51
End Page
S52
DOI
10.1016/j.jbiotec.2007.07.084

Use of Micropipet Manipulation Techniques to Measure the Properties of Giant Lipid Vesicles

Authors
Needham, D; Zhelev, D
MLA Citation
Needham, D, and Zhelev, D. "Use of Micropipet Manipulation Techniques to Measure the Properties of Giant Lipid Vesicles." Giant Vesicles: Perspectives in Supramolecular Chemistry. March 12, 2007. 102-147.
Source
scopus
Volume
6
Publish Date
2007
Start Page
102
End Page
147
DOI
10.1002/9780470511534.ch9

Functional bionetworks from nanoliter water droplets

We form networks from aqueous droplets by submerging them in an oil/lipid mixture. When the droplets are joined together, the lipid monolayers surrounding them combine at the interface to form a robust lipid bilayer. Various protein channels and pores can incorporate into the droplet-interface bilayer (DIB), and the application of a potential with electrodes embedded within the droplets allows ionic currents to be driven across the interface and measured. By joining droplets in linear or branched geometries, functional bionetworks can be created. Although the interfaces between neighboring droplets comprise only single lipid bilayers, the structures of the networks are long-lived and robust. Indeed, a single droplet can be "surgically" excised from a network and replaced with a new droplet without rupturing adjacent DIBs. Networks of droplets can be powered with internal "biobatteries" that use ion gradients or the light-driven proton pump bacteriorhodopsin. Besides their interest as coupled protocells, the droplets can be used as devices for ultrastable bilayer recording with greatly reduced electrolyte volume, which will permit their use in rapid screening applications. © 2007 American Chemical Society.

Authors
Holden, MA; Needham, D; Bayley, H
MLA Citation
Holden, MA, Needham, D, and Bayley, H. "Functional bionetworks from nanoliter water droplets." Journal of the American Chemical Society 129.27 (2007): 8650-8655.
PMID
17571891
Source
scival
Published In
Journal of the American Chemical Society
Volume
129
Issue
27
Publish Date
2007
Start Page
8650
End Page
8655
DOI
10.1021/ja072292a

Dynamics of neutrophil membrane compliance and microstructure probed with a micropipet-based piconewton force transducer

A novel biointerface probe was implemented to study the deformability of the neutrophil membrane and cortical cytoskeleton. Piconewton scale forces are applied to the cell using an ultrasensitive and tunable force transducer comprised of an avidin-coated microsphere attached to a biotinylated and swollen red blood cell. Deformations of freshly isolated human neutrophils were observed on the stage of an inverted phase contrast microscope. Force versus probe indentation curves over a cycle of contact, indentation, and retraction revealed three distinct material responses. Small probe deformations (∼ 500 nm) tested over a range of rates (e.g. 100-500 nm/s) revealed predominantly an elastic response. An initial low-slope region in the force-indentation curves (∼ 0.005 pN/nm), typically extending 0.5-1.0 μm from the cell surface was interpreted as probe contact with microvilli extensions. Further deformation yielded a slope of 0.054 ± 0.006 pN/nm, indicative of a stiffer cortical membrane. Disrupting cytoskeletal actin organization by pretreatment with cytochalasin D, reduced the slope by 40% to 0.033 ± 0.007 pN/nm and introduced hysteresis in the recovery phase. Modeling the neutrophil as a liquid drop with constant surface tension yielded values of cortical tension of 0.035 pN/nm for resting and 0.02 pN/nm for cytochalasin-treated neutrophils. These data demonstrate the utility of the biointerface probe for measuring local surface compliance and microstructure of living cells. © Biomedical Engineering Society 2007.

Authors
Simon, SI; Nyunt, T; Florine-Casteel, K; Ritchie, K; Ting-Beall, HP; Evans, E; Needham, D
MLA Citation
Simon, SI, Nyunt, T, Florine-Casteel, K, Ritchie, K, Ting-Beall, HP, Evans, E, and Needham, D. "Dynamics of neutrophil membrane compliance and microstructure probed with a micropipet-based piconewton force transducer." Annals of Biomedical Engineering 35.4 (2007): 595-604.
PMID
17370125
Source
scival
Published In
Annals of Biomedical Engineering
Volume
35
Issue
4
Publish Date
2007
Start Page
595
End Page
604
DOI
10.1007/s10439-007-9260-7

Phase I trial of doxorubicin-containing low temperature sensitive liposomes in spontaneous canine tumors.

PURPOSE: To determine the maximum tolerated dose, dose-limiting toxicities, and pharmacokinetic characteristics of doxorubicin encapsulated in a low temperature sensitive liposome (LTSL) when given concurrently with local hyperthermia to canine solid tumors. EXPERIMENTAL DESIGN: Privately owned dogs with solid tumors (carcinomas or sarcomas) were treated. The tumors did not involve bone and were located at sites amenable to local hyperthermia. LTSL-doxorubicin was given (0.7-1.0 mg/kg i.v.) over 30 minutes during local tumor hyperthermia in a standard phase I dose escalation study. Three treatments, given 3 weeks apart, were scheduled. Toxicity was monitored for an additional month. Pharmacokinetics were evaluated during the first treatment cycle. RESULTS: Twenty-one patients were enrolled: 18 with sarcomas and 3 with carcinomas. Grade 4 neutropenia and acute death secondary to liver failure, possibly drug related, were the dose-limiting toxicities. The maximum tolerated dose was 0.93 mg/kg. Other toxicities, with the possible exception of renal damage, were consistent with those observed following free doxorubicin administration. Of the 20 dogs that received > or = 2 doses of LTSL-doxorubicin, 12 had stable disease, and 6 had a partial response to treatment. Pharmacokinetic variables were more similar to those of free doxorubicin than the marketed liposomal product. Tumor drug concentrations at a dose of 1.0 mg/kg averaged 9.12 +/- 6.17 ng/mg tissue. CONCLUSION: LTSL-doxorubicin offers a novel approach to improving drug delivery to solid tumors. It was well tolerated and resulted in favorable response profiles in these patients. Additional evaluation in human patients is warranted.

Authors
Hauck, ML; LaRue, SM; Petros, WP; Poulson, JM; Yu, D; Spasojevic, I; Pruitt, AF; Klein, A; Case, B; Thrall, DE; Needham, D; Dewhirst, MW
MLA Citation
Hauck, ML, LaRue, SM, Petros, WP, Poulson, JM, Yu, D, Spasojevic, I, Pruitt, AF, Klein, A, Case, B, Thrall, DE, Needham, D, and Dewhirst, MW. "Phase I trial of doxorubicin-containing low temperature sensitive liposomes in spontaneous canine tumors." Clin Cancer Res 12.13 (July 1, 2006): 4004-4010.
PMID
16818699
Source
pubmed
Published In
Clinical cancer research : an official journal of the American Association for Cancer Research
Volume
12
Issue
13
Publish Date
2006
Start Page
4004
End Page
4010
DOI
10.1158/1078-0432.CCR-06-0226

Hyperthermia mediated liposomal drug delivery.

Drug delivery systems have been developed for cancer therapy in an attempt to increase the tumour drug concentration while limiting systemic exposure. Liposomes have achieved passive targeting of solid tumours through enhanced vascular permeability, which is greatly augmented by hyperthermia. However, anti-tumour efficacy has often been limited by slow release of bioavailable drug within the tumour. Local hyperthermia has become the most widely used stimulus for triggered release of liposomal drugs, through the use of specific lipids, polymers or other modifiers. A temperature-sensitive liposome containing doxorubicin has been shown to release 100% of contents through stabilized membrane pores within 10-20 s at 41 degrees C. This formulation has exhibited dramatic improvements in pre-clinical drug delivery and tumour regression and is now in clinical trials. Significantly, recent studies show that this liposome, in combination with local hyperthermia, exhibits vascular shutdown as a mechanism of anti-tumour effect that is not observed with free doxorubicin.

Authors
Ponce, AM; Vujaskovic, Z; Yuan, F; Needham, D; Dewhirst, MW
MLA Citation
Ponce, AM, Vujaskovic, Z, Yuan, F, Needham, D, and Dewhirst, MW. "Hyperthermia mediated liposomal drug delivery." Int J Hyperthermia 22.3 (May 2006): 205-213.
PMID
16754340
Source
pubmed
Published In
International Journal of Hyperthermia (Informa)
Volume
22
Issue
3
Publish Date
2006
Start Page
205
End Page
213
DOI
10.1080/02656730600582956

Microdroplet dissolution into a second-phase solvent using a micropipet technique: test of the Epstein-Plesset model for an aniline-water system.

The Epstein-Plesset model was originally derived for the dissolution of a single gas bubble in an infinite aqueous solution (Epstein, P. S.; Plesset, M. S. J. Chem. Phys. 1950, 18, 1505-1509). The micropipet manipulation technique was previously shown to test this theory on air microbubbles and air-filled lipid-coated microparticles accurately and appropriately (Duncan, P. B.; Needham, D. Langmuir 2004, 20, 2567-2578). This same theory is now tested to model liquid microdroplet dissolution in a well-defined solution environment. As presented previously for the gas-bubble system, holding a single microparticle at the end of a micropipet was not shown to affect the dissolution profile and allowed isotropic diffusion significantly, a necessary condition for the validation of the theory. Here, an aniline-water system with an initial droplet diameter of 50 microm was used as a model liquid-liquid system. A microdroplet of aniline in an aqueous solution presatureated with aniline at distinct levels was tested, as was the reverse system of a water droplet in an aniline solution. The dissolution lifetime was shown to increase with increasing medium saturation fraction according to the Epstein-Plesset time-dependent theory (including the time required to establish the stationary layer) neglecting interfacial tension. The droplet lifetime can be increased by an order of magnitude (from about 10 to 100 s) by increasing the saturation fraction from 0 to 0.9 and by another order of magnitude by increasing from 0.9 to 0.99. The technique proved to be an accurate and appropriate method to test the dissolution of single liquid microdroplets in a second liquid solution and establishes a systematic experimental and theoretical approach to the investigation of the formation of polymer and other microparticles.

Authors
Duncan, PB; Needham, D
MLA Citation
Duncan, PB, and Needham, D. "Microdroplet dissolution into a second-phase solvent using a micropipet technique: test of the Epstein-Plesset model for an aniline-water system." Langmuir 22.9 (April 25, 2006): 4190-4197.
PMID
16618164
Source
pubmed
Published In
Langmuir
Volume
22
Issue
9
Publish Date
2006
Start Page
4190
End Page
4197
DOI
10.1021/la053314e

Targeted bioavailability of drugs by triggered release from liposomes

Authors
Ponce, AM; Wright, A; Dewhirts, MW; Needham, D
MLA Citation
Ponce, AM, Wright, A, Dewhirts, MW, and Needham, D. "Targeted bioavailability of drugs by triggered release from liposomes." FUTURE LIPIDOLOGY 1.1 (February 2006): 25-34.
Source
wos-lite
Published In
Future lipidology
Volume
1
Issue
1
Publish Date
2006
Start Page
25
End Page
34
DOI
10.2217/17460875.1.1.25

New technology and clinical applications of nanomedicine: Highlights of the second annual meeting of the American Academy of Nanomedicine (Part I)

The Second Annual Meeting of the American Academy of Nanomedicine (AANM) was held at the National Acadmy of Science Building in Washinton, DC, September 9-10, 2006. The program included two Nobel Prize Laureate Lectures, two Keynote Lectures, and 123 invited outstanding State-in-Art lectures presenting in 23 special concurrent symposia. In addition, there were 22 poster presentations in the meeting addressing different areas in nanomedicine research. All of the presenters at the meeting are outstanding investigators and researchers in the field. The Second Annual Meeting of the AANM was a great success. The meeting provides investigators from different world areas a forum and an opportunity for discussion. We believe that nanomedicine research will develop rapidly in the future. The AANM invites basic and clinical researchers from the world to join this exciting research.

Authors
Wei, C; Lyubchenko, YL; Ghandehari, H; Hanes, J; Stebe, KJ; Mao, H-Q; Haynie, DT; Tomalia, DA; Foldvari, M; Monteiro-Riviere, N; al, E
MLA Citation
Wei, C, Lyubchenko, YL, Ghandehari, H, Hanes, J, Stebe, KJ, Mao, H-Q, Haynie, DT, Tomalia, DA, Foldvari, M, Monteiro-Riviere, N, and al, E. "New technology and clinical applications of nanomedicine: Highlights of the second annual meeting of the American Academy of Nanomedicine (Part I)." Nanomedicine: Nanotechnology, Biology, and Medicine 2.4 (2006): 253-263.
PMID
17292151
Source
scival
Published In
Nanomedicine: Nanotechnology, Biology and Medicine
Volume
2
Issue
4
Publish Date
2006
Start Page
253
End Page
263
DOI
10.1016/j.nano.2006.11.001

Temperature-triggered nanotechnology for chemotherapy: Rapid release from lysolipid temperature-sensitive liposomes

Lysolipid temperature-sensitive liposomes (LTSLs) demonstrate enhanced release of encapsulated drug contents via grain boundary permeabilization when heated to their phase transition temperature, resulting in dramatic in vivo tumor toxicity. Dithionite ion permeability and doxorubicin release were measured for lysolipid and nonlysolipid containing membranes to characterize and attempt to determine the mechanism behind the lysolipid-generated permeability enhancement. Results indicate that a dramatic enhancement in permeability and drug release begins about two degrees below the calorimetric peak of the liposome thermal transition, and extends several degrees past it. Lysolipid appears to not desorb from the liposomes during heating, but remains in the membranes stabilizing long lasting pores through which small molecules and drugs can freely diffuse. This is the basis for the temperature-triggered nanotechnology for drug release.

Authors
Mills, JK; Needham, D
MLA Citation
Mills, JK, and Needham, D. "Temperature-triggered nanotechnology for chemotherapy: Rapid release from lysolipid temperature-sensitive liposomes." 2006 NSTI Nanotechnology Conference and Trade Show - NSTI Nanotech 2006 Technical Proceedings 2 (2006): 5-8.
Source
scival
Published In
2006 NSTI Nanotechnology Conference and Trade Show - NSTI Nanotech 2006 Technical Proceedings
Volume
2
Publish Date
2006
Start Page
5
End Page
8

Lysolipid incorporation in dipalmitoylphosphatidylcholine bilayer membranes enhances the ion permeability and drug release rates at the membrane phase transition.

The enhanced permeability of lipid bilayer membranes at their gel-to-liquid phase transition has been explained using a "bilayer lipid heterogeneity" model, postulating leaky interfacial regions between still solid and melting liquid phases. The addition of lysolipid to dipalmitoylphosphatidylcholine bilayers dramatically enhances the amount of, and speed at which, encapsulated markers or drugs are released at this, already leaky, phase transition through these interfacial regions. To characterize and attempt to determine the mechanism behind lysolipid-generated permeability enhancement, dithionite permeability and doxorubicin release were measured for lysolipid and non-lysolipid, containing membranes. Rapid release of contents from lysolipid-containing membranes appears to occur through lysolipid-stabilized pores rather than a simple enhancement due to increased drug solubility in the bilayer. A dramatic enhancement in the permeability rate constant begins about two degrees below the calorimetric peak of the thermal transition, and extends several degrees past it. The maximum permeability rate constant coincides exactly with this calorimetric peak. Although some lysolipid desorption from liquid state membranes cannot be dismissed, dialyzation above T(m) and mass spectrometry analysis indicate lysolipid must, and can, remain in the membrane for the permeability enhancement, presumably as lysolipid stabilized pores in the grain boundary regions of the partially melted solid phase.

Authors
Mills, JK; Needham, D
MLA Citation
Mills, JK, and Needham, D. "Lysolipid incorporation in dipalmitoylphosphatidylcholine bilayer membranes enhances the ion permeability and drug release rates at the membrane phase transition." Biochim Biophys Acta 1716.2 (October 15, 2005): 77-96.
PMID
16216216
Source
pubmed
Published In
Biochimica et Biophysica Acta: international journal of biochemistry and biophysics
Volume
1716
Issue
2
Publish Date
2005
Start Page
77
End Page
96
DOI
10.1016/j.bbamem.2005.08.007

The effects of a complexation reaction on travelling wave-fronts in a quadratic autocatalytic system

A model which describes the effect that a complexation reaction can have on the propagation of reaction fronts in a quadratic autocatalytic system is considered. An initial-value problem is set up, which involves the (dimensionless) parameters K, the equilibrium constant for the complexation reaction, and σ, the initial concentration of the complexing agent. This initial-value problem is analysed, with global existence and uniqueness being established. Numerical integrations indicate the formation of permanent-form travelling waves at large times. The equations that govern the travelling waves in the model are treated in detail. It is determined that there is a minimum propagation speed υmin lying in the range υ0≡2/(1+σ)⩽υmin⩽2, with the value υ0 corresponding to the minimum speed derived from the linearization of the travelling wave equations. The existence of a curve C is established, which divides the (K,σ) parameter plane into two regions, one where υmin=υ0 and one where υmin> υ0 with waves propagating faster than their linearized speed in this region. The curve C is determined numerically together with the dependence of υmin on K and σ

Authors
Needham, DJ; Leach, JA; Merkin, JH
MLA Citation
Needham, DJ, Leach, JA, and Merkin, JH. "The effects of a complexation reaction on travelling wave-fronts in a quadratic autocatalytic system." Q. J. Mech. Appl. Math. (UK) 58 (2005): 577-599. (Academic Article)
Source
manual
Published In
Q. J. Mech. Appl. Math. (UK)
Volume
58
Publish Date
2005
Start Page
577
End Page
599
DOI
10.1093/qjmam/hbi022

Oligo-α-hydroxy ester cross-linkers: Impact of cross-linker structure on biodegradable hydrogel networks

We describe the synthesis of a series of biodegradable oligo-α-hydroxy ester cross-linkers and evaluate their impact on the degradation kinetics and macromolecule diffusion from a hydrogel network. By changing the steric and electronic environment at the site of degradation in the cross-linker, we were able to modulate the degradation, swelling kinetics, and corresponding release profiles of macromolecules from poly(HPMA) hydrogel networks under physiologically relevant conditions. As the steric hindrance and electron demand at the site of hydrolysis for three different cross-linkers was increased, the total time for the hydrogel network to completely dissolve increased from 2 to over 30 days while incubated in pH 7 buffer. As the number of hydrolyzable sites and the electron demand at the side of hydrolysis decreased, the time to completely dissolve decreased from weeks to several days. Increasing the cross-linking density for one of the degradable cross-linkers (1.5% to 3.0% feed ratio) increased the degradation time by several weeks. Burst release was absent for high molecular weight solutes because the release rate depended on controlled degradation of the polymer network and an increase in average network mesh size. The synthetically adaptable cross-linkers described herein offer a new approach for controlling the rate and extent of release from biodegradable hydrogel networks. © 2005 American Chemical Society.

Authors
Eichenbaum, KD; Thomas, AA; Eichenbaum, GM; Gibney, BR; Needham, D; Kiser, PF
MLA Citation
Eichenbaum, KD, Thomas, AA, Eichenbaum, GM, Gibney, BR, Needham, D, and Kiser, PF. "Oligo-α-hydroxy ester cross-linkers: Impact of cross-linker structure on biodegradable hydrogel networks." Macromolecules 38.26 (2005): 10757-10762.
Source
scival
Published In
Macromolecules
Volume
38
Issue
26
Publish Date
2005
Start Page
10757
End Page
10762
DOI
10.1021/ma0518306

A mathematical model for the spread of morphogens with density dependent chemosensitivity

A system of reaction-diffusion equations with volume-filling chemosensitivity arising in the modelling of morphogen spread during embryonic growth is considered. Existence and uniqueness of classical solutions to this novel system are established. Qualitative behaviour, including similarity structure of solutions, is developed. The existence of weak solutions in certain situations is established and periodic pulse solutions are obtained numerically. The biological interpretation of the results is discussed

Authors
Merkin, JH; Needham, DJ; Sleeman, BD
MLA Citation
Merkin, JH, Needham, DJ, and Sleeman, BD. "A mathematical model for the spread of morphogens with density dependent chemosensitivity." Nonlinearity (UK) 18.6 (2005): 2745-2773. (Academic Article)
Source
manual
Published In
Nonlinearity (UK)
Volume
18
Issue
6
Publish Date
2005
Start Page
2745
End Page
2773
DOI
10.1088/0951-7715/18/6/018

Test of the Epstein-Plesset model for gas microparticle dissolution in aqueous media: effect of surface tension and gas undersaturation in solution.

The gas from a free air bubble will readily dissolve in water, driven by two main factors: the concentration (undersaturation) of dissolved gas in the aqueous solution and the surface tension of the gas bubble-water interface via a Laplace overpressure in the bubble that this creates. This paper experimentally and theoretically investigates each of these effects individually. To study the effects of surface tension, single- and double-chain surfactants were utilized to control and define interfacial conditions of the microbubble in saturated solution. To study the effect of undersaturation, solid distearoylphosphocholine lipid was utilized to coat the gas microparticle with, essentially, a wax monolayer and to achieve zero tension in the surface. The experimental work was performed using a micromanipulation technique that allows one to create and micromanipulate single air microparticles (5-50 microm radius range) in infinite dilution and to accurately record the size of the particle as it loses volume due to the dissolution process. The micropipet technique has shown to be an improvement over other previous attempts to measure dissolution time with a 3.2% average experimental error in gas microparticle dissolution time. An ability to study a gas microparticle in infinite dilution in an isotropic diffusion field is in line with the theoretical assumptions and conditions of the Epstein-Plesset model. The Epstein-Plesset model on average underpredicted the experimentally determined dissolution time by 8.6%, where the effect of surface tension was considered with a range of surface tensions from 72 down to 25 mN/m. The Epstein-Plesset model on average overpredicted the dissolution time by 8.2%, where the effect of undersaturation was considered for a microparticle with zero tension in the surface (zero Laplace pressure) and a range of gas saturations from 70% to 100%. Compared to previous attempts in the literature, this paper more appropriately and accurately tests the Epstein-Plesset model for the dissolution of a single microbubble and an air-filled microparticle in aqueous solution.

Authors
Duncan, PB; Needham, D
MLA Citation
Duncan, PB, and Needham, D. "Test of the Epstein-Plesset model for gas microparticle dissolution in aqueous media: effect of surface tension and gas undersaturation in solution." Langmuir 20.7 (March 30, 2004): 2567-2578.
PMID
15835125
Source
pubmed
Published In
Langmuir
Volume
20
Issue
7
Publish Date
2004
Start Page
2567
End Page
2578

The materials engineering of temperature-sensitive liposomes.

Authors
Mills, JK; Needham, D
MLA Citation
Mills, JK, and Needham, D. "The materials engineering of temperature-sensitive liposomes." Methods Enzymol 387 (2004): 82-113.
PMID
15172159
Source
pubmed
Published In
Methods in Enzymology
Volume
387
Publish Date
2004
Start Page
82
End Page
113
DOI
10.1016/S0076-6879(04)87006-X

Mechanical properties and microstructure of polycrystalline phospholipid monolayer shells: Novel solid microparticles

A polycrystalline phospholipid monolayer self-assembled at the surface of an air microbubble in aqueous solution represents a novel material structure: in essence, a solid shell of wax with micrometer-scale dimensions and a thickness of only a single molecule. Micropipet manipulation of these microparticles revealed the dependence of the mechanical properties of the lipid shells, specifically, yield shear and shear viscosity, on the composition, grain microstructure, and thermal processing of the material, in particular the cooling rate of the shells from the melt. Properties were measured as a function of the (1) lipid composition at a fixed cooling rate and (2) cooling rate at a fixed lipid composition. Epifluorescent microscopy and transmission electron microscopy revealed that the morphology of the 1,2-distearoyl-sn-glycero-3-phosphatidylcholine monolayer microstructure, which develops upon freezing from the melt, is dependent on the cooling rate through the lipid transition temperature Tm, with larger micrograms being formed at slower cooling rates. Mechanical properties of the lipid shell follow micrograin size, with the coarse grain structure exhibiting a higher resistance to shear deformation than the fine grain structure does, which is behavior consistent with that of more traditional bulk crystalline materials.

Authors
Kim, DH; Costello, MJ; Duncan, PB; Needham, D
MLA Citation
Kim, DH, Costello, MJ, Duncan, PB, and Needham, D. "Mechanical properties and microstructure of polycrystalline phospholipid monolayer shells: Novel solid microparticles." Langmuir 19.20 (2003): 8455-8466.
Source
scival
Published In
Langmuir
Volume
19
Issue
20
Publish Date
2003
Start Page
8455
End Page
8466
DOI
10.1021/la034779c

Disc formation in cholesterol-free liposomes during phase transition

Cryogenic transmission electron microscopy (cryo-TEM) images of lysolipid-containing thermosensitive liposomes (LTSL) revealed that open liposomes and bilayer discs appeared when liposomes were cycled through the gel (Lβ′) to liquid-crystalline (Lα) phase transition. The amount of bilayer discs generated was dependent on the combined presence of PEG-lipid and lysolipid in the membrane. We hypothesize that micelle-forming membrane components stabilize the rim of bilayer openings and membrane discs that form when liposomes are cycled through TC. © 2003 Published by Elsevier B.V.

Authors
Ickenstein, LM; Arfvidsson, MC; Needham, D; Mayer, LD; Edwards, K
MLA Citation
Ickenstein, LM, Arfvidsson, MC, Needham, D, Mayer, LD, and Edwards, K. "Disc formation in cholesterol-free liposomes during phase transition." Biochimica et Biophysica Acta - Biomembranes 1614.2 (2003): 135-138.
PMID
12896806
Source
scival
Published In
Biochimica et Biophysica Acta - Biomembranes
Volume
1614
Issue
2
Publish Date
2003
Start Page
135
End Page
138
DOI
10.1016/S0005-2736(03)00196-2

Lipid Membranes: Biological Inspiration for Micro and Nano Encapsulation Technologies, Especially Drug Delivery

The development and performance of liposomes for releasing drug locally and in large amounts to affect tumor growth were discussed. The significance of inspired biological approach to micro and nano encapsulation technologies was also discussed. The mechanism of drug release was non-natural for the inspiration provided by nature's encapsulation technology. Various parameters for drug encapsulation such as drug retention, circulation half life, and thermally-triggered drug release were obtained from artificial lipid vesicles. The temperature-triggered liposome was developed for treating solid tumors.

Authors
Needham, D
MLA Citation
Needham, D. "Lipid Membranes: Biological Inspiration for Micro and Nano Encapsulation Technologies, Especially Drug Delivery." Materials Research Society Symposium - Proceedings 774 (2003): 173-202.
Source
scival
Published In
Materials Research Society Symposium - Proceedings
Volume
774
Publish Date
2003
Start Page
173
End Page
202

Evaluation of synthetic phospholipid ultrasound contrast agents.

The echogenic properties of synthetic, phospholipid encapsulated, air-filled microbubbles with various carbon-chain length as ultrasound contrast agents are investigated through the use of a flow-through laboratory ultrasound system. Specifically, we investigate the effect of shell carbon-chain length on the ultrasonic signal for a variety of flow rates. Averaged, integrated backscatter power measurements from the lipid encapsulated agents are benchmarked against those of Albunex (Albunex is a registered trademark of Molecular Biosystems, Inc., San Diego, CA), a commercially available, air-filled protein microbubbles contrast agent, approved for clinical use in echocardiography in the United States by the Food and Drug Administration. We find that the lipid encapsulated agents sustain less damage leading to gas dissolution or particle destruction as compared to Albunex in the slow-flow studies performed. The carbon-chain length of the encapsulating lipid molecule is shown not to observably affect the backscattered amplitude of ultrasound at flow velocities exceeding 7 mm/s.

Authors
Hasik, MJ; Kim, DH; Howle, LE; Needham, D; Prush, DP
MLA Citation
Hasik, MJ, Kim, DH, Howle, LE, Needham, D, and Prush, DP. "Evaluation of synthetic phospholipid ultrasound contrast agents." Ultrasonics 40.9 (November 2002): 973-982.
PMID
12385954
Source
pubmed
Published In
Ultrasonics
Volume
40
Issue
9
Publish Date
2002
Start Page
973
End Page
982

Evaluation of the effectiveness of UK community pharmacists' interventions in community palliative care.

In 1997, the Royal Pharmaceutical Society of Great Britain Working Party reported that UK community pharmacists had a crucial role in effective medicines management and effective symptom control for those receiving palliative care in the community. However, prior to the integration of community pharmacists into the community palliative team, it is necessary to evaluate the effectiveness of their pharmaceutical interventions.To assess the effectiveness of community pharmacists' clinical interventions in supporting palliative care patients in primary care using an independent multidisciplinary panel review.Patients with a life expectancy of less than 12 months were each registered with a single pharmacy and their consent was obtained for the community pharmacists to access their general practitioner (GP) case records. The community pharmacists received training in palliative pharmaceutical care and documenting interventions. The trained community pharmacists provided palliative pharmaceutical care to the recruited patients. At the end of a 10-month period, the clinical interventions were reviewed by an independent multidisciplinary expert panel consisting of a palliative care consultant, a Macmillan nurse (community palliative care nurse) and a hospital pharmacist with special interest in palliative care.Fourteen community palliative care teams (including community pharmacists, GPs and community nurses) took part in the study and 25 patients were recruited over the 10-month recording period. All but one patient had a diagnosis of cancer; the other patient had chronic obstructive pulmonary disease. By the end of the project, 14 patients had died. Community pharmacists recorded a total of 130 clinical interventions. Thirty interventions were excluded as insufficient information had been documented to allow review by the panel. Eighty-one per cent of the interventions were judged by the expert panel likely to be beneficial. However, 3% were judged likely to be detrimental to the patients' well-being.Most of the clinical interventions made by the community pharmacists for palliative pharmaceutical care were judged by the expert panel as being likely to be beneficial. The result supports the view that when community pharmacists are appropriately trained and included as integrated members of the team, they can intervene effectively to improve pharmaceutical care for palliative care patients.

Authors
Needham, DS; Wong, ICK; Campion, PD
MLA Citation
Needham, DS, Wong, ICK, and Campion, PD. "Evaluation of the effectiveness of UK community pharmacists' interventions in community palliative care." Palliative medicine 16.3 (May 2002): 219-225.
PMID
12046998
Source
epmc
Published In
Palliative Medicine
Volume
16
Issue
3
Publish Date
2002
Start Page
219
End Page
225
DOI
10.1191/0269216302pm533oa

Interactions of pH-sensitive peptides and polymers with lipid bilayers: Binding and membrane stability

The controlled release of content from liposomes is critical for their successful use as drug delivery systems. The most commonly used triggering mechanisms for content release are changes in the environment, such as a change in temperature or pH. In this case, the structure of the liposome membrane changes either by itself or by the presence of environmentally sensitive molecules, which leads to a change of membrane permeability. In this chapter we discuss the interaction of pH-sensitive molecules, such as the influenza fusion peptide mutant AcE4K and the polymer poly(2-ethylacrylic acid), with 1-stearoyl-2-oleoyl-sn-glycero-3-phosphocholine membranes. We emphasize the ability of these molecules to rearrange the structure of the membrane. This ability is derived from the strength of molecular binding to the membrane interface as well as from the cohesiveness of the membrane itself. The binding of molecules to the membrane has been studied extensively; however, the coupling between binding and membrane cohesiveness is a relatively uncharted area. The binding of pH-sensitive molecules to the membrane is coupled with their protonation, whereas membrane cohesiveness depends on membrane composition. A simple model is introduced where the binding to the membrane and the work for displacing the membrane lipids and creating a vacancy for the binding molecules determine the outcome of the event. The work for creating a vacancy is dependent on membrane cohesiveness, and can be increased by adding cholesterol. The model predicts that the addition of cholesterol will increase the threshold pH for content release. The experimental data fit very well to the predictions of the model. This effect provides an opportunity for designing systems to release drugs in environments of unique pH, such as tumor tissues and endosome interiors. © 2002.

Authors
Zhelev, DV; Needham, D
MLA Citation
Zhelev, DV, and Needham, D. "Interactions of pH-sensitive peptides and polymers with lipid bilayers: Binding and membrane stability." Current Topics in Membranes 52 (2002): 437-464.
Source
scival
Published In
Current Topis in Membranes
Volume
52
Publish Date
2002
Start Page
437
End Page
464

The development and testing of a new temperature-sensitive drug delivery system for the treatment of solid tumors.

Our laboratories have been working together in close collaboration for over 10 years concerning the design and performance of lipid-based drug delivery systems. Over the past 3 years we have conceived of, developed, and tested pre-clinically, a new liposome-based temperature-sensitive drug delivery system for the treatment of solid tumors. This work is reported in a series of four publications: "J. Liposome Res. 9 (1999) 491; Cancer Res. Adv. Brief 60(5) (2000) 1197; Cancer Res. 6(9) (2000) 748; and Cancer Res. 60 (2000) 6950". Following a brief introduction concerning the motivations behind the work, this article will review these studies, including some of our earlier work that led to these ideas, and will present the rational design of the new liposome formulation from a materials engineering perspective.

Authors
Needham, D; Dewhirst, MW
MLA Citation
Needham, D, and Dewhirst, MW. "The development and testing of a new temperature-sensitive drug delivery system for the treatment of solid tumors." Adv Drug Deliv Rev 53.3 (December 31, 2001): 285-305. (Review)
PMID
11744173
Source
pubmed
Published In
Advanced Drug Delivery Reviews
Volume
53
Issue
3
Publish Date
2001
Start Page
285
End Page
305

Interaction of synthetic HA2 influenza fusion peptide analog with model membranes.

The interaction of the synthetic 21 amino acid peptide (AcE4K) with 1-oleoyl-2-[caproyl-7-NBD]-sn-glycero-3-phosphocholine membranes is used as a model system for the pH-sensitive binding of fusion peptides to membranes. The sequence of AcE4K (Ac-GLFEAIAGFIENGWEGMIDGK) is based on the sequence of the hemagglutinin HA2 fusion peptide and has similar partitioning into phosphatidylcholine membranes as the viral peptide. pH-dependent partitioning in the membrane, circular dichroism, tryptophan fluorescence, change of membrane area, and membrane strength, are measured to characterize various key aspects of the peptide-membrane interaction. The experimental results show that the partitioning of AcE4K in the membrane is pH dependent. The bound peptide inserts in the membrane, which increases the overall membrane area in a pH-dependent manner, however the depth of insertion of the peptide in the membrane is independent of pH. This result suggests that the binding of the peptide to the membrane is driven by the protonation of its three glutamatic acids and the aspartic acid, which results in an increase of the number of bound molecules as the pH decreases from pH 7 to 4.5. The transition between the bound state and the free state is characterized by the Gibbs energy for peptide binding. This Gibbs energy for pH 5 is equal to -30.2 kJ/mol (-7.2 kcal/mol). Most of the change of the Gibbs energy during the binding of AcE4K is due to the enthalpy of binding -27.3 kJ/mol (-6.5 kcal/mol), while the entropy change is relatively small and is on the order of 6.4 J/mol.K (2.3 cal/mol.K). The energy barrier separating the bound and the free state, is characterized by the Gibbs energy of the transition state for peptide adsorption. This Gibbs energy is equal to 51.3 kJ/mol (12.3 kcal/mol). The insertion of the peptide into the membrane is coupled with work for creation of a vacancy for the peptide in the membrane. This work is calculated from the measured area occupied by a single peptide molecule (220 A(2)) and the membrane elasticity (190 mN/m), and is equal to 15.5 kJ/mol (3.7 kcal/mol). The comparison of the work for creating a vacancy and the Gibbs energy of the transition state shows that the work for creating a vacancy may have significant effect on the rate of peptide insertion and therefore plays an important role in peptide binding. Because the work for creating a vacancy depends on membrane elasticity and the elasticity of the membrane is dependent on membrane composition, this provides a tool for modulating the pH for membrane instability by changing membrane composition. The insertion of the peptide in the membrane does not affect the membrane permeability for water, which shows that the peptide does not perturb substantially the packing of the hydrocarbon region. However, the ability of the membrane to retain solutes in the presence of peptide is compromised, suggesting that the inserted peptide promotes formation of short living pores. The integrity of the membrane is substantially compromised below pH 4.8 (threshold pH), when large pores are formed and the membrane breaks down. The binding of the peptide in the pore region is reversible, and the pore size varies on the experimental conditions, which suggests that the peptide in the pore region does not form oligomers.

Authors
Zhelev, DV; Stoicheva, N; Scherrer, P; Needham, D
MLA Citation
Zhelev, DV, Stoicheva, N, Scherrer, P, and Needham, D. "Interaction of synthetic HA2 influenza fusion peptide analog with model membranes." Biophys J 81.1 (July 2001): 285-304.
PMID
11423414
Source
pubmed
Published In
Biophysical Journal
Volume
81
Issue
1
Publish Date
2001
Start Page
285
End Page
304
DOI
10.1016/S0006-3495(01)75699-8

Equilibrium and dynamic interfacial tension measurements at microscopic interfaces using a micropipet technique - 2. Dynamics of phospholipid monolayer formation and equilibrium tensions at the water-air interface

Equilibrium and dynamic interfacial tension measurements were performed using micropipet technique. Dynamics of phospholipid monolayer formation and equilibrium tensions at the water-air interface were studied. Results showed that the surface tension and the rate of formation of lipid monolayers depended strongly on their relative phase transition temperature.

Authors
Lee, S; Kim, DH; Needham, D
MLA Citation
Lee, S, Kim, DH, and Needham, D. "Equilibrium and dynamic interfacial tension measurements at microscopic interfaces using a micropipet technique - 2. Dynamics of phospholipid monolayer formation and equilibrium tensions at the water-air interface." Langmuir 17.18 (2001): 5544-5550.
Source
scival
Published In
Langmuir
Volume
17
Issue
18
Publish Date
2001
Start Page
5544
End Page
5550
DOI
10.1021/la0103261

Equilibrium and Dynamic Interfacial Tension Measurements at Microscopic Interfaces Using a Micropipet Technique. 1. A New Method for Determination of Interfacial Tension

A new micropipet technique has been developed to measure the equilibrium and dynamic interfacial tensions of microscopic liquid-gas and liquid-liquid interfaces. In this technique, a liquid-gas or liquid-liquid interface with a radius of curvature ranging from 1 to 100 μm can be created inside a tapered micropipet. On the basis of the Laplace equation (a work balance between tension and applied pressure for the curved interface), the equilibrium interfacial tension between the two phases (clean or surfactant adsorbed) can be determined by measuring the radius of curvature of the interface for a series of pressure changes. With an additional surfactant-delivering micropipet, we show how this technique also offers an effective way to study adsorption/desorption dynamics upon exposure and washout for various surfactants and provides the whole history of surfactant exchange for microscopic interfaces. Here, we verify that the results of this technique are consistent with the interfacial tension values previously obtained by other methods typically conducted on macroscopic interfaces. The technique has been used to study the adsorption of PEG-40-Stearate as a monolayer at the liquid-gas interface. From a plot of the measured surface tension as a function of PEG-40-Stearate concentration, the critical micelle concentration and area per molecule have been determined to be 40 ± 2 μM and 1.19 nm 2, respectively. In a companion paper, we report additional new data on a series of phospholipid monolayers.

Authors
Lee, S; Kim, DH; Needham, D
MLA Citation
Lee, S, Kim, DH, and Needham, D. "Equilibrium and Dynamic Interfacial Tension Measurements at Microscopic Interfaces Using a Micropipet Technique. 1. A New Method for Determination of Interfacial Tension." Langmuir 17.18 (2001): 5537-5543.
Source
scival
Published In
Langmuir
Volume
17
Issue
18
Publish Date
2001
Start Page
5537
End Page
5543
DOI
10.1021/la0103259

Erratum: pH and ion-triggered volume responses of anionic hydrogel microspheres (Macromolecules (July 28, 1998) 31:15 (5084-5093))

Authors
Eichenbaum, GM; Kiser, PF; Simon, SA; Needham, D
MLA Citation
Eichenbaum, GM, Kiser, PF, Simon, SA, and Needham, D. "Erratum: pH and ion-triggered volume responses of anionic hydrogel microspheres (Macromolecules (July 28, 1998) 31:15 (5084-5093))." Macromolecules 34.20 (2001): 7230-. (Academic Article)
Source
manual
Published In
Macromolecules
Volume
34
Issue
20
Publish Date
2001
Start Page
7230
DOI
10.1021/ma012488

Erratum: Investigation of the swelling response and loading of ionic microgels with drugs and proteins; The dependence on cross-link density (Macromolecules (July 27, 1999) 32:15 (4867-4878))

Authors
Eichenbaum, GM; Kiser, PF; Dobrynin, AV; Simon, SA; Needham, D
MLA Citation
Eichenbaum, GM, Kiser, PF, Dobrynin, AV, Simon, SA, and Needham, D. "Erratum: Investigation of the swelling response and loading of ionic microgels with drugs and proteins; The dependence on cross-link density (Macromolecules (July 27, 1999) 32:15 (4867-4878))." Macromolecules 34.18 (2001): 6526-. (Academic Article)
Source
manual
Published In
Macromolecules
Volume
34
Issue
18
Publish Date
2001
Start Page
6526
DOI
10.1021/ma0124892

Efficacy of liposomes and hyperthermia in a human tumor xenograft model: importance of triggered drug release.

The tumor drug concentrations, drug distributions, and therapeutic efficacies achieved by three fundamentally different liposomes, nonthermosensitive liposome (NTSL), traditional thermosensitive liposome (TTSL), and low temperature sensitive liposome (LTSL); free doxorubicin (DOX); and saline in combination with hyperthermia (HT) were directly compared in a human tumor xenograft model. NTSL is a nonthermosensitive liposome in the physiological temperature range, TTSL is a traditional thermosensitive liposome that triggers in the range of approximately 42-45 degrees C and releases drug over approximately 30 min, and LTSL is a new low temperature sensitive liposome that triggers in the range of approximately 39-40 degrees C and releases drug in a matter of seconds. Because of the different attributes of the liposomes, it was possible to delineate the relative importance of liposome drug encapsulation, HT cytotoxicity, HT-drug interaction, HT-induced liposomal delivery, and HT-triggered liposomal drug release in achieving antitumor activity. Athymic nude mice bearing the FaDu human tumor xenograft were given a single i.v. dose of 5 mg/kg of DOX (free drug or liposome encapsulated), and the tumors were then heated to either 34 degrees C or 42 degrees C for 1 h at 34 degrees C. All treatment groups were similar, achieving low concentrations of DOX (0-4.5 ng/mg). At 42 degrees C, the LTSL (25.6 ng/mg) achieved the highest DOX concentration (P < 0.04), but all three liposomal formulations (7.3-25.6 ng/mg) were higher than saline or DOX (0-0.7 ng/mg; P < 0.02). LTSL + HT was also the only group that resulted in significant amounts of DNA-bound DOX (silver nitrate-extractable fraction; P < 0.02). Tumor tissue sections were visualized for DOX fluorescence to investigate the local distribution of the drug in the tumor and confirm the relative drug concentrations based on fluorescence intensity. There was relatively little fluorescence seen with treatment groups at 34 degrees C. At 42 degrees C, the LTSL showed the most DOX fluorescence (P < 0.01), and the fluorescence, although not homogeneous, was pervasive throughout the tumor sections. Therapeutic efficacy of treatments was determined from tumor growth time. At 34 degrees C, the only treatment group significantly better than the saline group (9.8 days) was the NTSL group, with a growth time of 20.9 days (P < 0.02). At 42 degrees C, all three liposomal formulations were more efficacious than DOX. LTSL + HT had the longest growth time (51.4 days) and the most number of local controls at 60 days (six of nine tumors). With HT, the DOX concentrations and fluorescence were tightly correlated with tumor growth delay, indicating that adequate (increased) drug delivery can be predictive of therapeutic effect. Overall, the LTSL + HT group showed the largest DOX concentration, the highest and most pervasive DOX fluorescence, and the most antitumor effect. Thus, HT-triggered liposomal drug release may account for the largest differential therapeutic effect and demonstrates the importance of rapid drug release from the drug carriers at the tumor site.

Authors
Kong, G; Anyarambhatla, G; Petros, WP; Braun, RD; Colvin, OM; Needham, D; Dewhirst, MW
MLA Citation
Kong, G, Anyarambhatla, G, Petros, WP, Braun, RD, Colvin, OM, Needham, D, and Dewhirst, MW. "Efficacy of liposomes and hyperthermia in a human tumor xenograft model: importance of triggered drug release." Cancer Res 60.24 (December 15, 2000): 6950-6957.
PMID
11156395
Source
pubmed
Published In
Cancer Research
Volume
60
Issue
24
Publish Date
2000
Start Page
6950
End Page
6957

PEG-covered lipid surfaces: bilayers and monolayers.

In this review paper we survey the ways in which various micropipet techniques have been used to study the mechanochemical and interactive features of lipid bilayer vesicles and monolayer-coated gas bubbles. Special emphasis will be made on characterizing the barrier properties of grafted PEG layers and how a hierarchical approach that uses a short barrier and extended ligand allows us to start to mimic nature's own solution to the problem of ubiquitous repulsion and specific attraction. The information gained from such studies not only characterizes the membrane and other lipid surfaces and their intersurface interactions from a fundamental materials science perspective, but also provides essential materials property data that are required for the successful design and deployment of lipid-based carriers and other capsules in applications involving this so-called 'stealthy' surface.

Authors
Needham, D; Kim, DH
MLA Citation
Needham, D, and Kim, DH. "PEG-covered lipid surfaces: bilayers and monolayers." Colloids Surf B Biointerfaces 18.3-4 (October 1, 2000): 183-195.
PMID
10915943
Source
pubmed
Published In
Colloids and Surfaces B: Biointerfaces
Volume
18
Issue
3-4
Publish Date
2000
Start Page
183
End Page
195

Hyperthermia increases accumulation of technetium-99m-labeled liposomes in feline sarcomas.

The effect of hyperthermia on the accumulation of technetium-99m-labeled liposomes was studied in feline sarcomas. Each cat received two separate injections of liposomes. The first was used to quantify the amount of technetium-99m-labeled liposomes within the tumor under normothermic conditions. The second injection was made at the beginning of a 60-min hyperthermia procedure. Planar scintigraphy was used to measure the activity of technetium-99m-labeled liposomes within the tumor at predetermined times up to 18 h after injection. Regions of interest were drawn for the tumor, lungs, liver, kidney, and aorta. Counts in the regions of interest were decay corrected. Counts/pixel in the tumor under normothermic and hyperthermic conditions were normalized to aorta counts/pixel. A total of 16 cats were eligible for the study. In two of the 16 cats, incomplete count data precluded analysis. In the remaining 14 cats, hyperthermia resulted in a significant increase in liposome accumulation in the tumor (P = 0.001). Tumor volume ranged from 1.2 to 236.2 cm3, and thermal dose ranged from 2.0 to 243.3 CEM43CT90 (equivalent time that the 10th percentile temperature was equal to 43 degrees C). There was not a relationship between either tumor volume or hyperthermia dose on the magnitude of increased liposome accumulation, suggesting that this method has application across a range of tumor volumes and degrees of heatibility.

Authors
Matteucci, ML; Anyarambhatla, G; Rosner, G; Azuma, C; Fisher, PE; Dewhirst, MW; Needham, D; Thrall, DE
MLA Citation
Matteucci, ML, Anyarambhatla, G, Rosner, G, Azuma, C, Fisher, PE, Dewhirst, MW, Needham, D, and Thrall, DE. "Hyperthermia increases accumulation of technetium-99m-labeled liposomes in feline sarcomas." Clin Cancer Res 6.9 (September 2000): 3748-3755.
PMID
10999769
Source
pubmed
Published In
Clinical cancer research : an official journal of the American Association for Cancer Research
Volume
6
Issue
9
Publish Date
2000
Start Page
3748
End Page
3755

Water permeability and mechanical strength of polyunsaturated lipid bilayers.

Micropipette aspiration was used to test mechanical strength and water permeability of giant-fluid bilayer vesicles composed of polyunsaturated phosphatidylcholine PC lipids. Eight synthetic-diacyl PCs were chosen with 18 carbon chains and degrees of unsaturation that ranged from one double bond (C18:0/1, C18:1/0) to six double bonds per PC molecule (diC18:3). Produced by increasing pipette pressurization, membrane tensions for lysis of single vesicles at 21 degrees C ranged from approximately 9 to 10 mN/m for mono- and dimono-unsaturated PCs (18:0/1, 18:1/0, and diC18:1) but dropped abruptly to approximately 5 mN/m when one or both PC chains contained two cis-double bonds (C18:0/2 and diC18:2) and even lower approximately 3 mN/m for diC18:3. Driven by osmotic filtration following transfer of individual vesicles to a hypertonic environment, the apparent coefficient for water permeability at 21 degrees C varied modestly in a range from approximately 30 to 40 microm/s for mono- and dimono-unsaturated PCs. However, with two or more cis-double bonds in a chain, the apparent permeability rose to approximately 50 microm/s for C18:0/2, then strikingly to approximately 90 microm/s for diC18:2 and approximately 150 microm/s for diC18:3. The measurements of water permeability were found to scale exponentially with the reduced temperatures reported for these lipids in the literature. The correlation supports the concept that increase in free volume acquired in thermal expansion above the main gel-liquid crystal transition of a bilayer is a major factor in water transport. Taken together, the prominent changes in lysis tension and water permeability indicate that major changes occur in chain packing and cohesive interactions when two or more cis-double bonds alternate with saturated bonds along a chain.

Authors
Olbrich, K; Rawicz, W; Needham, D; Evans, E
MLA Citation
Olbrich, K, Rawicz, W, Needham, D, and Evans, E. "Water permeability and mechanical strength of polyunsaturated lipid bilayers." Biophys J 79.1 (July 2000): 321-327.
PMID
10866958
Source
pubmed
Published In
Biophysical Journal
Volume
79
Issue
1
Publish Date
2000
Start Page
321
End Page
327
DOI
10.1016/S0006-3495(00)76294-1

A new temperature-sensitive liposome for use with mild hyperthermia: characterization and testing in a human tumor xenograft model.

The single biggest challenge now facing drug delivery (for liposomes and indeed other carriers) is to initiate and produce release of the encapsulated drug only at the diseased site and at controllable rates. Our efforts have focused on developing a new thermal-sensitive drug delivery system, specifically for the local control of solid tumors. We describe here a new lipid formulation containing doxorubicin that has been optimized for both mild hyperthermic temperatures (39 degrees C to 40 degrees C) that are readily achievable in the clinic and rapid release times of drug (tens of seconds). This new liposome, in combination with mild hyperthermia, was found to be significantly more effective than free drug or current liposome formulations at reducing tumor growth in a human squamous cell carcinoma xenograft line (FaDu), producing 11 of 11 complete regressions lasting up to 60 days posttreatment.

Authors
Needham, D; Anyarambhatla, G; Kong, G; Dewhirst, MW
MLA Citation
Needham, D, Anyarambhatla, G, Kong, G, and Dewhirst, MW. "A new temperature-sensitive liposome for use with mild hyperthermia: characterization and testing in a human tumor xenograft model." Cancer Res 60.5 (March 1, 2000): 1197-1201.
PMID
10728674
Source
pubmed
Published In
Cancer Research
Volume
60
Issue
5
Publish Date
2000
Start Page
1197
End Page
1201

Effect of chain length and unsaturation on elasticity of lipid bilayers

Micropipette pressurization of giant bilayer vesicles was used to measure both elastic bending k(c) and area stretch K(A) moduli of fluid-phase phosphatidylcholine (PC) membranes. Twelve diacyl PCs were chosen: eight with two 18 carbon chains and degrees of unsaturation from one double bond (C18:1/0, C18:0/1) to six double bonds per lipid (diC18:3), two with short saturated carbon chains (diC13:0, diC14:0), and two with long unsaturated carbon chains (diC20:4, diC22:1). Bending moduli were derived from measurements of apparent expansion in vesicle surface area under very low tensions (0.001-0.5 mN/m), which is dominated by smoothing of thermal bending undulations. Area stretch moduli were obtained from measurements of vesicle surface expansion under high tensions (>0.5 mN/m), which involve an increase in area per molecule and a small - but important - contribution from smoothing of residual thermal undulations. The direct stretch moduli varied little (< ± 10%) with either chain unsaturation or length about a mean of 243 mN/m. On the other hand, the bending moduli of saturated/monounsaturated chain PCs increased progressively with chain length from 0.56 x 10-19 J for diC13:0 to 1.2 x 10-19 J for diC22:1. However, quite unexpectedly for longer chains, the bending moduli dropped precipitously to ~0.4 x 10-19 J when two or more cis double bonds were present in a chain (C18:0/2, diC18:2, diC18:3, diC20:4). Given nearly constant area stretch moduli, the variations in bending rigidity with chain length and polyunsaturation implied significant variations in thickness. To test this hypothesis, peak-to-peak headgroup thicknesses h(pp) of bilayers were obtained from x-ray diffraction of multibilayer arrays at controlled relative humidities. For saturated/monounsaturated chain bilayers, the distances h(pp) increased smoothly from diC13:0 to diC22:1 as expected. Moreover, the distances and elastic properties correlated well with a polymer brush model of the bilayer that specifies that the elastic ratio (k(c)/K(A))(1/2) = (h(pp) - h(o))/24, where h(o) ≃ 1 nm accounts for separation of the headgroup peaks from the deformable hydrocarbon region. However, the elastic ratios and thicknesses for diC18:2, diC18:3, and diC20:4 fell into a distinct group below the correlation, which showed that poly-cis unsaturated chain bilayers are thinner and more flexible than saturated/monounsaturated chain bilayers.

Authors
Rawicz, W; Olbrich, KC; McIntosh, T; Needham, D; Evans, EA
MLA Citation
Rawicz, W, Olbrich, KC, McIntosh, T, Needham, D, and Evans, EA. "Effect of chain length and unsaturation on elasticity of lipid bilayers." Biophysical Journal 79.1 (2000): 328-339.
PMID
10866959
Source
scival
Published In
Biophysical Journal
Volume
79
Issue
1
Publish Date
2000
Start Page
328
End Page
339
DOI
10.1016/S0006-3495(00)76295-3

Design and performance of poly(HPMA) hydrogels containing symmetrical biodegradable crosslinkers composed of oligo-lactate and oligo-glycolate esters

The synthesis and testing of the first symmetrical based on vinylic oligomers of α-hydroxy acids are described. Biodegradable gel networks with chemically defined crosslinks were made and studied and were shown to degrade at a defined rate in response to the environment in which they are bathed. The degradation rate of gels composed of the crosslinkers conform to the known order of importance of steric and electronic effects in ester hydrolysis, as well as the concentration of acid or base. The advantages of the crosslinkers over related technologies are discussed. The oligomers were characterized by nuclear magnetic resonance (NMR) spectroscopy.

Authors
Kiser, PF; Thomas, AA; Eichenbaum, GM; Needham, D; Kim, I
MLA Citation
Kiser, PF, Thomas, AA, Eichenbaum, GM, Needham, D, and Kim, I. "Design and performance of poly(HPMA) hydrogels containing symmetrical biodegradable crosslinkers composed of oligo-lactate and oligo-glycolate esters." American Chemical Society, Polymer Preprints, Division of Polymer Chemistry 41.1 (2000): 712-713.
Source
scival
Published In
American Chemical Society, Polymer Preprints, Division of Polymer Chemistry
Volume
41
Issue
1
Publish Date
2000
Start Page
712
End Page
713

The influence of tiered layers of surface-grafted poly(ethylene glycol) on receptor-ligand-mediated adhesion between phospholipid monolayer-stabilized microbubbles and coated glass beads

The goal of the current study is to measure the strength of specific adhesion between a prototypical phospholipid-stabilized ultrasound contrast agent, the surface of which has been derivatized with a ligand molecule, and a glass bead surface coated with the corresponding receptor. In particular, the role of surface architecture (the size and density of surface-grafted molecules) in mediating adhesion is examined. The ligand surface density on bubble shells is varied by changing the mole ratios of shell components [lipid: poly(ethylene glycol) (PEG)ylated surfactant stabilizer:ligand-lipid] during preparation. Two receptor-ligand systems are tested: avidin-biotin and antifluorescein-fluorescein. The central investigative method is a novel application of the micromanipulation technique in which an individual microbubble and a glass bead are captured by separate pipets in an aqueous environment and brought into adhesive contact with each other. Aspiration pressure applied by the bead pipet is incrementally increased until the level efforce required to detach the bead from the bubble is exerted. The micromanipulation technique offers the advantage that a single adhesion event can be observed under controlled conditions, and the force required to effect bubble detachment is determined from pressure and system geometry. The strength of adhesion is examined as a function of composition and structure of the lipid shell and the receptor-ligand pair. The success of adhesion between surfaces is dependent on the availability of ligand proximal to the steric barrier of surface PEG. If the ligand is attached to the shell via a PEG spacer longer than that of the PEG stabilizer, then adhesion succeeds; if the ligand is not on an extended spacer, adhesion fails. Adhesion strength increases and plateaus with increasing ligand-lipid concentration. Such phenomena must be considered when engineering a targetable stabilized contrast agent. © 2000 American Chemical Society.

Authors
Kim, DH; Klibanov, AL; Needham, D
MLA Citation
Kim, DH, Klibanov, AL, and Needham, D. "The influence of tiered layers of surface-grafted poly(ethylene glycol) on receptor-ligand-mediated adhesion between phospholipid monolayer-stabilized microbubbles and coated glass beads." Langmuir 16.6 (2000): 2808-2817.
Source
scival
Published In
Langmuir
Volume
16
Issue
6
Publish Date
2000
Start Page
2808
End Page
2817

An IDL to Ada95 mapping to support propagation modeling

Representing dynamic interdependencies between design objects is an essential part of modeling the critical software communications found in complex software systems. This paper investigates the modeling of propagations (our term for dynamic interdependencies), which are captured using design-level triggers for specifying dynamic behavior across object types. We focus on the CORBA-compliant utilization of our propagation model to support distributed, propagation-focused applications. We develop a propagation-specific interface in IDL (Interface Definition Language), and examine Ada 95 source code that meets the requirements specified by the IDL design. An example of the CORBA-compliant propagations involved in the maintenance of topological invariance in the industrial domain is examined

Authors
Needham, D; Demurjian, S; Peters, T
MLA Citation
Needham, D, Demurjian, S, and Peters, T. "An IDL to Ada95 mapping to support propagation modeling." Ada Lett. (USA) 20.1 (2000): 58-66. (Academic Article)
Source
manual
Published In
Ada Lett. (USA)
Volume
20
Issue
1
Publish Date
2000
Start Page
58
End Page
66

Alkali earth metal binding properties of ionic microgels

Spherical micron-sized (4-10 μm in diameter) poly(methacrylic acid-co-acrylic acid) microgels were synthesized by precipitation polymerization, and their chelation reactions with chloride salts of Mg2+, Ca2+, Sr2+, and Ba2+ were investigated by isothermal titration calorimetry (ITC). Ion concentrations obtained by inductively coupled-plasma mass spectrometry (ICP-MS) were used to obtain binding constants and to verify the results obtained by ITC. Although the two methods agreed within 20%, the ITC measurements were experimentally easier to obtain and more accurate. Interference contrast microscopy and micropipet manipulation techniques were used to measure the volume change and corresponding dehydration of the microgels as a function of divalent ion type and concentration. The ITC results showed that the addition of MCl2 electrolytes, where M represents a divalent metal, with the microgels was an entropy driven reaction in that ΔG approx. -20 kJ/mol ≅ TΔS. These data suggest that the free energy driving the ion exchange (M2+ divalent ions for monovalent Na+) is the result of the increase in the entropy of the system; this entropy increase is due to (1) water being 'squeezed' from the microgels into the bulk solution and (2) the collapse of the entropy elastic network that accompanies the decrease in the volume of the microgels.

Authors
Eichenbaum, GM; Kiser, PF; Shah, D; Meuer, WP; Needham, D; Simon, SA
MLA Citation
Eichenbaum, GM, Kiser, PF, Shah, D, Meuer, WP, Needham, D, and Simon, SA. "Alkali earth metal binding properties of ionic microgels." Macromolecules 33.11 (2000): 4087-4093.
Source
scival
Published In
Macromolecules
Volume
33
Issue
11
Publish Date
2000
Start Page
4087
End Page
4093
DOI
10.1021/ma9917139

AnkB, a periplasmic ankyrin-like protein in Pseudomonas aeruginosa, is required for optimal catalase B (KatB) activity and resistance to hydrogen peroxide

In this study, we have cloned the ankB gene, encoding an ankyrin-like protein in Pseudomonas aeruginosa. The ankB gene is composed of 549 bp encoding a protein of 183 amino acids that possesses four 33-amino-acid ankyrin repeats that are a hallmark of erythrocyte and brain ankyrins. The location of ankB is 57 bp downstream of katB, encoding a hydrogen peroxide- inducible catalase, KatB. Monomeric AnkB is a 19.4-kDa protein with a pI of 5.5 that possesses 22 primarily hydrophobic amino acids at residues 3 to 25, predicting an inner-membrane-spanning motif with the N terminus in the cytoplasm and the C terminus in the periplasm. Such an orientation in the cytoplasmic membrane and, ultimately, periplasmic space was confirmed using AnkB-BlaM and AnkB-PhoA protein fusions. Circular dichroism analysis of recombinant AnkB minus its signal peptide revealed a secondary structure that is ~65% α-helical. RNase protection and KatB- and AnkB-LacZ translational fusion analyses indicated that katB and ankB are part of a small operon whose transcription is induced dramatically by H2O2, and controlled by the global transactivator OxyR. Interestingly, unlike the spherical nature of ankyrin- deficient erythrocytes, the cellular morphology of an ankB mutant was identical to that of wild-type bacteria, yet the mutant produced more membrane vesicles. The mutant also exhibited a fourfold reduction in KatB activity and increased sensitivity to H2O2, phenotypes that could be complemented in trans by a plasmid constitutively expressing ankB. Our results suggest that AnkB may form an antioxidant scaffolding with KatB in the periplasm at the cytoplasmic membrane, thus providing a protective lattice work for optimal H2O2 detoxification.

Authors
Howell, ML; Alsabbagh, E; Ma, J-F; Ochsner, UA; Klotz, MG; Beveridge, TJ; Blumenthal, KM; Niederhoffer, EC; Morris, RE; Needham, D; al, E
MLA Citation
Howell, ML, Alsabbagh, E, Ma, J-F, Ochsner, UA, Klotz, MG, Beveridge, TJ, Blumenthal, KM, Niederhoffer, EC, Morris, RE, Needham, D, and al, E. "AnkB, a periplasmic ankyrin-like protein in Pseudomonas aeruginosa, is required for optimal catalase B (KatB) activity and resistance to hydrogen peroxide." Journal of Bacteriology 182.16 (2000): 4545-4556.
PMID
10913088
Source
scival
Published In
Journal of Bacteriology
Volume
182
Issue
16
Publish Date
2000
Start Page
4545
End Page
4556
DOI
10.1128/JB.182.16.4545-4556.2000

Lipid-coated microgels for the triggered release of doxorubicin

We have systematically engineered a polymeric, multi-component drug delivery system composed of a lipid-coated hydrogel microparticle (microgel). The design of this delivery system was motivated by the recent elucidation of the mechanism of regulated secretion from the secretory granule and the compositional and structural features that underlie its ability to store and release endogenous drug-like compounds. The present work describes the assembly and response of a prototype construct which displays several important features of the secretory granule, including its high drug loading capacity, and triggered microgel swelling, resulting in the burst release of drug. To achieve this, ionic microgels were synthesized, and loaded with doxorubicin via ion exchange. These microgels were then coated with a lipid bilayer, and the release of doxorubicin was triggered from the gels using either lipid-solubilizing surfactants or electroporation. The use of a microanalytical technique is featured utilizing micropipette manipulation that allows the study of the behavior of individual microparticles. The lipid-coated microgels were electroporated in saline solution; they swelled and disrupted their bilayer coating over a period of several seconds and exchanged doxorubicin with the external plasma saline over a period of several minutes. It is envisioned that this system will ultimately find utility in drug delivery systems that are designed to release chemotherapeutic agents and peptides by the application of a triggering signal. Copyright (C) 2000 Elsevier Science B.V.

Authors
Kiser, PF; Wilson, G; Needham, D
MLA Citation
Kiser, PF, Wilson, G, and Needham, D. "Lipid-coated microgels for the triggered release of doxorubicin." Journal of Controlled Release 68.1 (2000): 9-22.
PMID
10884575
Source
scival
Published In
Journal of Controlled Release
Volume
68
Issue
1
Publish Date
2000
Start Page
9
End Page
22
DOI
10.1016/S0168-3659(00)00236-4

An expert panel review to evaluate the effectiveness of community pharmacist's interventions in the palliative care setting

Authors
Needham, D; Wong, I
MLA Citation
Needham, D, and Wong, I. "An expert panel review to evaluate the effectiveness of community pharmacist's interventions in the palliative care setting." September 18, 1999.
Source
scopus
Published In
The Pharmaceutical journal
Volume
263
Issue
7063 SUPPL. 1
Publish Date
1999

Materials engineering of lipid bilayers for drug carrier performance

An account is given on recent advances in the design and characterization of liposomes. Focus is on connecting the the performance of liposomes to their properties and composition. The important of research in drug transport and release is stressed in view of exciting new results in tumor-growth-delay studies.

Authors
Needham, D
MLA Citation
Needham, D. "Materials engineering of lipid bilayers for drug carrier performance." MRS Bulletin 24.10 (1999): 32-40.
Source
scival
Published In
MRS Bulletin
Volume
24
Issue
10
Publish Date
1999
Start Page
32
End Page
40

Investigation of the swelling response and loading of ionic microgels with drugs and proteins: the dependence on cross-link density

The pH and NaCl induced swelling response and drug and protein loading of poly(methacrylic acid-co-acrylic acid) microgels (4-10 μm diameter) were measured as a function of cross-link density. The swelling ratio (Q) of the microgels increased linearly from 2 to 12 when the mole fraction of cross-linking monomer decreased from 0.25 to 0.10 (at pH's > 5.3). In the presence of 5 M NaCl (at pH's > 5.3), microgels with cross-linking feed ratios of 0.25 and 0.10 swelled to only 80% and 60% of their maximum volume measured at low ionic strength, respectively. To determine the average pore size in the different cross-linking density microgels (feed ratios = 0.25, 0.20, 0.15, and 0.10), we measured the size cutoffs for the uptake of different sized proteins. On the basis of these size exclusion experiments, we calculated the number of monomers between cross-links in each of these gels to be 6.5, 9.5, 12.5, and 16.5, respectively. These values were used in our theoretical modeling of the network swelling (modified Flory-Huggins thermodynamic model) to predict the pH-Q dependence for different degrees of cross-linking. The model predictions of the microgel pH swelling response as a function of cross-link density were in good quantitative agreement with experiments. Experimentally, the loading of smaller drug molecules did not have clear molecular weight dependence for the different cross-link density microgels. However, differences in the loading behavior of these molecules on the basis of their partition coefficients indicated that binding affinity, molecular packing, and condensation were important factors that need to be explored to optimized microgels for use in specific drug delivery applications.

Authors
Eichenbaum, GM; Kiser, PF; Dobrynin, AV; Simon, SA; Needham, D
MLA Citation
Eichenbaum, GM, Kiser, PF, Dobrynin, AV, Simon, SA, and Needham, D. "Investigation of the swelling response and loading of ionic microgels with drugs and proteins: the dependence on cross-link density." Macromolecules 32.15 (1999): 4867-4878.
Source
scival
Published In
Macromolecules
Volume
32
Issue
15
Publish Date
1999
Start Page
4867
End Page
4878
DOI
10.1021/ma981945s

Investigation of the swelling response and drug loading of ionic microgels: The dependence on functional group composition

Spherical micron-sized (4-7 μm diameter) poly(methacrylic acid-co-nitrophenyl acrylate) microgels were synthesized by precipitation polymerization and selectively derivatized with carboxylic acid, glutamic acid, hydroxamic acid, sulfonic acid, and ethanol functional groups in five separate post-polymerization reactions. The pH and NaCl induced swelling response, drug loading, capacity (`capacity' = total number of functional ionic groups that bind protons), and density of the five different composition anionic microgels, each containing a different functional group as well as a baseline of carboxylic acid groups, were measured. Using the micropipet flow technique, it was found that the pH range of the swelling response for the five different microgel compositions shifted by an amount that was proportional to the solution pKa's of their functional groups. The degree of drug loading increased in proportion to the microgels' capacity. However, the drug loading did not decrease proportionately when the capacity was lowered.

Authors
Eichenbaum, GM; Kiser, PF; Shah, D; Simon, SA; Needham, D
MLA Citation
Eichenbaum, GM, Kiser, PF, Shah, D, Simon, SA, and Needham, D. "Investigation of the swelling response and drug loading of ionic microgels: The dependence on functional group composition." Macromolecules 32.26 (1999): 8996-9006.
Source
scival
Published In
Macromolecules
Volume
32
Issue
26
Publish Date
1999
Start Page
8996
End Page
9006
DOI
10.1021/ma9908393

Effect of bilayer cholesterol and surface grafted poly(ethylene glycol) on pH-induced release of contents from liposomes by poly(2-ethylacrylic acid)

Liposomal delivery systems have yet to reach the levels of burst release of drug at a diseased site necessary to achieve high local therapeutic levels. A pH sensitive, triggered release system, is one mechanism which shows great promise, especially for use in low pH environments such as tumor interstitial space and endosomes. The pH-sensitive polymer, poly(2- ethylacrylic acid) (PEAA), has been shown to disrupt liposome membranes and release entrapped contents, dependent on membrane compressibility. By adding cholesterol to lipid bilayers, the pH at which entrapped contents were released was reduced from pH 6.7 for a pure lipid system, to pH 6.0 for a cholesterol-saturated system. This decrease in pH, corresponding to an increase in the degree of protonation (i.e. degree of hydrophobicity), was directly correlated to the increase in the elastic area expansion modulus of the bilayers. These results are presented in terms of a balance between polymer solubility and membrane expansion. In a separate experiment, the inclusion of a PEG barrier (5 mol% PEG-2000-lipid) did not prevent PEAA from inducing contents release. This demonstrates that highly hydrated polymeric layers are not effective barriers for other water soluble polymers, and the results may even point to some association between the two polymers.

Authors
Mills, JK; Eichenbaum, G; Needham, D
MLA Citation
Mills, JK, Eichenbaum, G, and Needham, D. "Effect of bilayer cholesterol and surface grafted poly(ethylene glycol) on pH-induced release of contents from liposomes by poly(2-ethylacrylic acid)." Journal of Liposome Research 9.2 (1999): 275-290.
Source
scival
Published In
Journal of Liposome Research
Volume
9
Issue
2
Publish Date
1999
Start Page
275
End Page
290

Enhancement of the phase transition permeability of DPPC liposomes by incorporation of MPPC: A new temperature-sensitive liposome for use with mild hyperthermia

The present study describes a novel method of preparing thermosensitive liposomes by compositional modification, incorporating a highly bilayer compatible lysolipid, 1-Palmitoyl-2-Hydroxy-sn-Glycero-3-Phosphocholine (MPPC) into the gel phase liposomes composed of 1,2-Dipalmitoyl-sn-Glycero-3- Phosphocholine (DPPC). This compositional modification of the liposomes achieved a significantly enhanced release of entrapped liposome contents at mild hyperthermic temperatures between 39°C-40°C as compared to pure DPPC which released only 20% of contents over a broader range of 40°C-45°C, and the more conventional (DPPC/DSPC-based) temperature-sensitive liposomes that released more slowly in the 43°C-45°C range. Also, the temperature range over which the maximum release occurred for the DPPC: MPPC system remained very narrow and maximum release is achieved after only a tens of seconds of heating. Characterization of the liposome formulation was carried out by studying the release profiles of entrapped carboxyfluorescein from the liposomes at various temperatures and time intervals. The cumulative release profiles of the formulation were correlated with differential scanning calorimetric scans of the same compositions in order to understand the molecular mechanisms associated with the release of entrapped marker. The stability and thermal sensitivity of the liposomes in the presence of phosphate buffered saline and human serum albumin were evaluated. The new concept for triggered release presented here is that upon raising the temperature of the gel phase liposome to 39°C-40°C, the desorption of MPPC from liquid phase regions as the first lipid begins to melt creates enhanced defect formation which dramatically increases the permeability of the membrane to the entrapped CF.

Authors
Anyarambhatla, GR; Needham, D
MLA Citation
Anyarambhatla, GR, and Needham, D. "Enhancement of the phase transition permeability of DPPC liposomes by incorporation of MPPC: A new temperature-sensitive liposome for use with mild hyperthermia." Journal of Liposome Research 9.4 (1999): 491-506.
Source
scival
Published In
Journal of Liposome Research
Volume
9
Issue
4
Publish Date
1999
Start Page
491
End Page
506

Attachment of ligands to gas-filled microbubbles via PEG spacer and lipid residues anchored at the interface

Authors
Klibanov, AL; Gu, H; Wojdyla, JK; Jr, WJH; Kim, DH; Needham, D; Villanueva, FS; Brandenburger, GH
MLA Citation
Klibanov, AL, Gu, H, Wojdyla, JK, Jr, WJH, Kim, DH, Needham, D, Villanueva, FS, and Brandenburger, GH. "Attachment of ligands to gas-filled microbubbles via PEG spacer and lipid residues anchored at the interface." Proceedings of the Controlled Release Society 26 (1999): 124-125.
Source
scival
Published In
Proceedings of the Controlled Release Society
Issue
26
Publish Date
1999
Start Page
124
End Page
125

Targeted drug delivery

Creating effective targeted drug delivery strategies is an integral component of the overall process of drug development. The four key requirements of an effective drug delivery system are retain, evade, target and release. Increasing the therapeutic index (TI) of a delivered compound by selectively delivering it to target areas is a goal that has many obstacles. Some of these concerns have been addressed by recent developments in areas such as liposomes, prodrugs, external targeting, controlled gene expression and antibodies. An analysis of some of the relevant inventions is discussed below. In order to present these inventions in a new light, materials science and engineering approaches have been used to examine the patents and help discuss their advantages and disadvantages. Patents concerning the manipulation of genes and proteins are at the core of this research and are an integral part of its future. Very specific targeting is possible when working at this level. The most exciting developments combine targeting strategies for delivery systems with many layers of specificity, increasing their targeting potential. It is also important to understand (and possibly exploit) the area to which a delivery system is being targeted and to learn from nature's own delivery systems. Examples of these systems, including the red blood cell, the neutrophil and the secretory granule, are discussed using a materials engineering approach. This analysis reveals numerous characteristics that nature has designed into its delivery systems, and how these are important when creating man-made products. Working with these kinds of ideas, a true 'magic bullet' may be discovered.

Authors
Mills, JK; Needham, D
MLA Citation
Mills, JK, and Needham, D. "Targeted drug delivery." Expert Opinion on Therapeutic Patents 9.11 (1999): 1499-1513.
Source
scival
Published In
Expert Opinion on Therapeutic Patents
Volume
9
Issue
11
Publish Date
1999
Start Page
1499
End Page
1513
DOI
10.1517/13543776.9.11.1499

A synthetic mimic of the secretory granule for drug delivery.

Secretory cells contain submicroscopic granules composed of a polyanionic polymer network that is collapsed owing to the presence of hydronium ions and weak base cations. The network is encapsulated within a lipid membrane, and functions as a vehicle for the osmotically inert storage of a variety of granule-bound endogenous mediator species, such as histamine, serotonin and proteases. These species are excreted from the granule and thence from the cell in response to external biochemical signals. Hydrogels that swell and shrink in response to external stimuli might serve as synthetic analogues of secretory granules. Here we describe the systematic engineering of multi-component, environmentally responsive hydrogel microspheres, coated with a lipid bilayer to mimic more closely the natural secretory granule. These microspheres exhibit pH- and ion-dependent volume phase transitions and ion-sensitive exchange of bound cations when the encapsulating lipid membrane is porated. We stimulated poration electrically in individual microgel particles immobilized and manipulated with a micropipette. This system could find use for the triggered release of encapsulated drugs in the body.

Authors
Kiser, PF; Wilson, G; Needham, D
MLA Citation
Kiser, PF, Wilson, G, and Needham, D. "A synthetic mimic of the secretory granule for drug delivery." Nature 394.6692 (July 30, 1998): 459-462.
PMID
9697768
Source
pubmed
Published In
Nature
Volume
394
Issue
6692
Publish Date
1998
Start Page
459
End Page
462
DOI
10.1038/28822

pH and Ion-Triggered Volume Response of Anionic Hydrogel Microspheres.

Micrometer-sized (4-7 µm diameter) poly(methacrylic acid) (PMAA) hydrogel microspheres were synthesized by precipitation polymerization. Individual microspheres were held in a micropipet and visualized by interference contrast microscopy. They were characterized with regard to their mass, density, water content, electrophoretic mobility, and apparent pKa. Equilibrium changes in volume were measured as functions of the pH and NaCl concentration of the suspending solution. The maximum reduction in the microsphere equilibrium volume (Vrmax) at pH 3.0 was 0.28, where Vr was the ratio of the microsphere volume at the test pH to its volume at pH 6.6. A Donnan-based thermodynamic model, modified to include counterion binding because of the high fixed charge density in the microspheres (3.0 M), was applied to determine the difference in the ion concentration between the interior and exterior of the gel. The ion concentration differences (which were related to the osmotic pressure) predicted by the model were proportional to the microsphere equilibrium volume with changing pH and salt concentration. This supported the hypothesis that the equilibrium volume of the microspheres was set by a force balance between the osmotic pressure and the elasticity of the hydrogel matrix. Microspheres changed from their maximum equilibrium volume at pH 6.6 to their minimum equilibrium volume at pH 3.0 in 300 ms. This indicated that diffusion of the polymer matrix and not diffusion of ions into and out of the microsphere was the rate-limiting factor in determining a microsphere's swelling rate.

Authors
Eichenbaum, GM; Kiser, PF; Simon, SA; Needham, D
MLA Citation
Eichenbaum, GM, Kiser, PF, Simon, SA, and Needham, D. "pH and Ion-Triggered Volume Response of Anionic Hydrogel Microspheres." Macromolecules 31.15 (July 28, 1998): 5084-5093.
PMID
9680449
Source
pubmed
Published In
Macromolecules
Volume
31
Issue
15
Publish Date
1998
Start Page
5084
End Page
5093
DOI
10.1021/ma970897t

Centre families in two-dimensional complex holomorphic dynamical systems

We consider a two-dimensional complex holomorphic dynamical system. In particular, we use the singular point theory of C.H. Briot and J.C. Bouquet to establish the existence of complex holomorphic invariant manifolds of the system in the neighbourhood of an equilibrium point with two purely imaginary eigenvalues. Consequently, this enables us to establish the existence of isochronous centre families in the neighbourhood of the equilibrium point. The results are exhibited by application to the complex Takens-Bogdanov system

Authors
Needham, DJ; McAllister, S
MLA Citation
Needham, DJ, and McAllister, S. "Centre families in two-dimensional complex holomorphic dynamical systems." Proc. R. Soc. Lond. A, Math. Phys. Eng. Sci. (UK) 454.1976 (1998): 2267-2278. (Academic Article)
Source
manual
Published In
Proc. R. Soc. Lond. A, Math. Phys. Eng. Sci. (UK)
Volume
454
Issue
1976
Publish Date
1998
Start Page
2267
End Page
2278
DOI
10.1098/rspa.1998.0258

Adsorption, molecular exchange and defect formation in membranes

The past year has seen significant advances in our understanding of the key factors involved in determining whether a macromolecule or colloidal particle can reach, bind to, and absorb into lipid bilayer membranes. The highlights include the need to combine both electrostatic and hydrophobic interactions to achieve stable binding, the influence of membrane dipoles, the molecular-scale filter provided by grafted polymers, and the recognition that surfactants and peptides form defects that depend on their aggregated state in the membrane.

Authors
Needham, D; McIntosh, TJ; Simon, SA; Zhelev, D
MLA Citation
Needham, D, McIntosh, TJ, Simon, SA, and Zhelev, D. "Adsorption, molecular exchange and defect formation in membranes." Current Opinion in Colloid and Interface Science 3.5 (1998): 511-517.
Source
scival
Published In
Current Opinion in Colloid and Interface Science
Volume
3
Issue
5
Publish Date
1998
Start Page
511
End Page
517

Interactions between poly(2-ethylacrylic acid) and lipid bilayer membranes: effects of cholesterol and grafted poly(ethylene glycol).

The exchange of the protonatable polymer, poly(2-ethylacrylic acid) (PEAA), has been studied with vesicle membranes containing cholesterol from 0 to 60 mol% or PEG2000-lipid (5 mol%). The release of an entrapped dye from 100 nm extruded liposomes was used as an assay for membrane perturbation by the polymer as a function of pH. The inclusion of cholesterol was found to reduce the pH at which the polymer caused release of the dye from the lipid vesicles, and the degree of polymer protonation (i.e., degree of hydrophobicity) correlated well with the increase in elastic expansion modulus of the vesicle bilayer. The results are discussed in terms of a balance between polymer solubility and membrane expansion. With respect to the PEG barrier, the presence of 5 mol% PEG2000, which represents full surface coverage, did not prevent PEAA from inducing contents release, demonstrating that highly hydrated polymeric layers are not effective barriers for other water soluble polymers, and may point to some association between the two polymers.

Authors
Needham, D; Mills, J; Eichenbaum, G
MLA Citation
Needham, D, Mills, J, and Eichenbaum, G. "Interactions between poly(2-ethylacrylic acid) and lipid bilayer membranes: effects of cholesterol and grafted poly(ethylene glycol)." Faraday Discuss 111 (1998): 103-110.
PMID
10822603
Source
pubmed
Published In
Faraday Discussions
Issue
111
Publish Date
1998
Start Page
103
End Page
110

Binding of paclitaxel to lipid interfaces: Correlations with interface compliance

In the present work, we have studied the paclitaxel loading efficiency of lipid bilayers with respect to their compositional behavior, which in turn determines their mechanical properties. We have found that, if a drug with a low water solubility like paclitaxel (or at least a part of this molecule) associates with lipid bilayers, then binding is enhanced if the interface was soft, i.e., highly expandable (low elastic area modulus and tensile strength). We have systematically varied the surface softness of stearoyl oleoyl phosphatidylcholine (SOPC) bilayers by incorporating the lysolipid, monooleoyl phosphatidylcholine (MOPC) to create maximum softness and 50 mol% cholesterol (CHOL) to create less soft, and more stiff membranes, respectively. It was observed that the least soft SOPC bilayers (high elastic area modulus and tensile strength) composed of 50 mol% CHOL, load a negligible amount of paclitaxel (~5μM) in comparison to soft SOPC bilayers made by the incorporation of 28 mol% MOPC, which load 2 mM paclitaxel (12 mol% paclitaxel with respect to total lipid). The paclitaxel loading can be increased to almost 20 mol% for the ultimate in 'soft' interfaces, the lysolipid.

Authors
Needham, D; Sarpal, RS
MLA Citation
Needham, D, and Sarpal, RS. "Binding of paclitaxel to lipid interfaces: Correlations with interface compliance." Journal of Liposome Research 8.2 (1998): 147-163.
Source
scival
Published In
Journal of Liposome Research (Informa)
Volume
8
Issue
2
Publish Date
1998
Start Page
147
End Page
163

Exchange of monooleoylphosphatidylcholine as monomer and micelle with membranes containing poly(ethylene glycol)-lipid.

Surface-grafted polymers, such as poly(ethylene glycol) (PEG), provide an effective steric barrier against surface-surface and surface-macromolecule interactions. In the present work, we have studied the exchange of monooleoylphosphatidylcholine (MOPC) with vesicle membranes containing 750 mol wt surface-grafted PEG (incorporated as PEG-lipid) from 0 to 20 mol % and have analyzed the experimental results in terms of thermodynamic and stationary equilibrium models. Micropipette manipulation was used to expose a single lipid vesicle to a flow of MOPC solution (0.025 microM to 500 microM). MOPC uptake was measured by a direct measure of the vesicle area change. The presence of PEG(750) lipid in the vesicle membrane inhibited the partitioning of MOPC micelles (and to some extent microaggregates) into the membrane, while even up to 20 mol % PEG-lipid, it did not affect the exchange of MOPC monomers both into and out of the membrane. The experimental data and theoretical models show that grafted PEG acts as a very effective molecular scale "filter" and prevents micelle-membrane contact, substantially decreasing the apparent rate and amount of MOPC taken up by the membrane, thereby stabilizing the membrane in a solution of MOPC that would otherwise dissolve it.

Authors
Needham, D; Stoicheva, N; Zhelev, DV
MLA Citation
Needham, D, Stoicheva, N, and Zhelev, DV. "Exchange of monooleoylphosphatidylcholine as monomer and micelle with membranes containing poly(ethylene glycol)-lipid." Biophys J 73.5 (November 1997): 2615-2629.
PMID
9370456
Source
pubmed
Published In
Biophysical Journal
Volume
73
Issue
5
Publish Date
1997
Start Page
2615
End Page
2629
DOI
10.1016/S0006-3495(97)78291-2

Mimicking the smart polymer matrix of the secretory granule: a new concept in controlled release drug delivery

Regulated secretion of biological molecules is controlled by specialized secretory cells. The design of a multi-component drug delivery system which can closely mimic the properties of the secretary granule will have utility for triggered release of drugs. This study demonstrates the potential of a synthetic, smart polymer system which mimics the smart polymer matrix of secretory cells in phase transition behavior.

Authors
Kiser, PF; Needham, D; Wilson, G
MLA Citation
Kiser, PF, Needham, D, and Wilson, G. "Mimicking the smart polymer matrix of the secretory granule: a new concept in controlled release drug delivery." Polymeric Materials Science and Engineering, Proceedings of the ACS Division of Polymeric Materials Science and Engineering 76 (1997): 226--.
Source
scival
Published In
Polymeric Materials Science and Engineering, Proceedings of the ACS Division of Polymeric Materials Science and Engineering
Volume
76
Publish Date
1997
Start Page
226-

Barrier properties of surface-grafted PEG for macromolecule-surface interactions

Authors
Needham, D; Noppl-Simson, D
MLA Citation
Needham, D, and Noppl-Simson, D. "Barrier properties of surface-grafted PEG for macromolecule-surface interactions." American Chemical Society, Polymer Preprints, Division of Polymer Chemistry 38.1 (1997): 549-550.
Source
scival
Published In
American Chemical Society, Polymer Preprints, Division of Polymer Chemistry
Volume
38
Issue
1
Publish Date
1997
Start Page
549
End Page
550

Avidin-biotin interactions at vesicle surfaces: adsorption and binding, cross-bridge formation, and lateral interactions.

Densely packed domains of membrane proteins are important structures in cellular processes that involve ligand-receptor binding, receptor-mediated adhesion, and macromolecule aggregation. We have used the biotin-avidin interaction at lipid vesicle surfaces to mimic these processes, including the influence of a surface grafted polymer, polyethyleneglycol (PEG). Single vesicles were manipulated by micropipette in solutions of fluorescently labeled avidin to measure the rate and give an estimate of the amount of avidin binding to a biotinylated vesicle as a function of surface biotin concentration and surface-grafted PEG as PEG-lipid. The rate of avidin adsorption was found to be four times less with 2 mol% PEG750 than for the unmodified surface, and 10 mol% PEG completely inhibited binding of avidin to biotin for a 2-min incubation. Using two micropipettes, an avidin-coated vesicle was presented to a biotinylated vesicle. In this vesicle-vesicle adhesion test, the accumulation of avidin in the contact zone was observed, again by using fluorescent avidin. More importantly, by controlling the vesicle membrane tension, this adhesion test provided a direct measure of the spreading pressure of the biotin-avidin-biotin cross-bridges confined in the contact zone. Assuming ideality, this spreading pressure gives the concentration of avidin cross-bridges in the contact zone. The rate of cross-bridge accumulation was consistent with the diffusion of the lipid-linked "receptors" into the contact zone. Once adherent, the membranes failed in tension before they could be peeled apart. PEG750 did not influence the mechanical equilibrium because it was not compressed in the contact zone, but it did perform an important function by eliminating all nonspecific adhesion. This vesicle-vesicle adhesion experiment, with a lower tension limit of 0.01 dyn/cm, now provides a new and useful method with which to measure the spreading pressures and therefore colligative properties of a range of membrane-bound macromolecules.

Authors
Noppl-Simson, DA; Needham, D
MLA Citation
Noppl-Simson, DA, and Needham, D. "Avidin-biotin interactions at vesicle surfaces: adsorption and binding, cross-bridge formation, and lateral interactions." Biophys J 70.3 (March 1996): 1391-1401.
PMID
8785294
Source
pubmed
Published In
Biophysical Journal
Volume
70
Issue
3
Publish Date
1996
Start Page
1391
End Page
1401
DOI
10.1016/S0006-3495(96)79697-2

Biomembrane templates for nanoscale conduits and networks

Long nanotubes of fluid-lipid bilayers can be used to create templates for photochemical polymerization into solid-phase conduits and networks. Each nanotube is pulled from a micropipette-held feeder vesicle by mechanical retraction of the vesicle after molecular bonding to a rigid substrate. The caliber of the tube is controlled precisely in a range from 20 to 200 nanometers merely by setting the suction pressure in the micropipette. Branched conduits can be formed by coalescing separate nanotubes drawn serially from the feeder vesicle surface. Single nanotubes and nanotube junctions can be linked together between bonding sites on a surface to create a functionalized network. After assembly, the templates can be stabilized by photoinitiated radical cross-linking of macromonomers contained in the aqueous solution confined by the lipid bilayer boundary.

Authors
Evans, E; Bowman, H; Leung, A; Needham, D; Tirrell, D
MLA Citation
Evans, E, Bowman, H, Leung, A, Needham, D, and Tirrell, D. "Biomembrane templates for nanoscale conduits and networks." Science 273.5277 (1996): 933-935.
PMID
8688071
Source
scival
Published In
Science
Volume
273
Issue
5277
Publish Date
1996
Start Page
933
End Page
935

Nanometer-scale polymeric patterns and networks

Authors
Bowman, H; Evans, E; Needham, D; Tirrell, DA
MLA Citation
Bowman, H, Evans, E, Needham, D, and Tirrell, DA. "Nanometer-scale polymeric patterns and networks." Polymeric Materials Science and Engineering, Proceedings of the ACS Division of Polymeric Materials Science and Engineering 74 (1996): 437-. (Academic Article)
Source
manual
Published In
Polymeric Materials Science and Engineering, Proceedings of the ACS Division of Polymeric Materials Science and Engineering
Volume
74
Publish Date
1996
Start Page
437

Pore formation and pore dynamics in bilayer membranes

Authors
Zhelev, DV; Needham, D
MLA Citation
Zhelev, DV, and Needham, D. "Pore formation and pore dynamics in bilayer membranes." American Society of Mechanical Engineers, Bioengineering Division (Publication) BED 34 (1996): 47-49.
Source
scival
Published In
American Society of Mechanical Engineers, Bioengineering Division (Publication) BED
Volume
34
Publish Date
1996
Start Page
47
End Page
49

Reaction-diffusion model for autocatalytic polymerization: II. The initial value problem

An initial-boundary value problem arising from a simple model for radical chain polymerization is discussed in detail. General properties of the solution are derived first and it is shown that a moving interface develops. This separates a region where the polymer is sufficiently concentrated for it to be immobile from one where it is still free to diffuse. An asymptotic analysis is performed in this latter region, where it is shown that a permanent-form travelling wave (treated in Part I) develops in the long time structure and that this wave travels with its minimum possible speed. Numerical results for the full initial-boundary value problem are presented which confirm the asymptotic theory and give results in regions not accessible to this analysis.

Authors
Needham, DJ; King, AC; Merkin, JH
MLA Citation
Needham, DJ, King, AC, and Merkin, JH. "Reaction-diffusion model for autocatalytic polymerization: II. The initial value problem." IMA Journal of Applied Mathematics (Institute of Mathematics & Its Applications) 56.1 (1996): 65-86. (Academic Article)
Source
manual
Published In
IMA Journal of Applied Mathematics (Institute of Mathematics & Its Applications)
Volume
56
Issue
1
Publish Date
1996
Start Page
65
End Page
86

Experimental tests for protrusion and undulation pressures in phospholipid bilayers.

Theoretical treatments predict that strong entropic pressures between adjacent bilayer membranes can arise from out of plane motions caused by either thermally induced bending undulations of the entire bilayer [Harbich, W., & Helfrich, W. (1984) Chem. Phys. Lipids 36, 39-63; Evans, E. A., & Parsegian, V. A. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 7132-7136] or protrusions of individual lipid molecules from the bilayer surface [Israelachvili, J. N., & Wennerström, H. (1992) J. Phys. Chem. 96, 520-531]. To determine the relative contributions of these motions to the repulsive pressure between phospholipid bilayers, the osmotic stress/X-ray diffraction method was used to measure the range and magnitude of the total repulsive pressure, and micropipet methods were used to measure the bending moduli of phosphatidylcholine bilayers containing lysophosphatidylcholine and polyunsaturated diarachidonoylphosphatidylcholine (DAPC) bilayers. In the gel phase, incorporation of equimolar lysophosphatidylcholine into phosphatidylcholine bilayers caused the hydrocarbon chains from apposing monolayers to interdigitate, but did not appreciably change the equilibrium fluid spacing in excess buffer from its control value of 12 A. In contrast, the incorporation of equimolar lysophosphatidylcholine into liquid-crystalline phase phosphatidylcholine bilayers markedly increased the range of the repulsive pressure so that equilibrium fluid separation increased from 15 to 28 A, and also decreased the bilayer bending modulus from 5.1 x 10(-13) to 1.3 x 10(-13) erg. Liquid-crystalline DAPC bilayers had intermediate values of both equilibrium fluid separation (20 A) and bending modulus (2.8 x 10(-13) erg). Analysis of these data indicates that (1) the relative importance of entropic pressures compared to the hydration pressure depends strongly on the composition and structure of the bilayer, (2) the protrusion pressure may contribute to the total repulsive pressure at large pressures or small fluid spacings, and (3) the repulsive undulation pressure, together with the attractive van der Waals pressure, is a primary factor in determining the fluid spacing at low and/or zero applied pressures in liquid-crystalline bilayers.

Authors
McIntosh, TJ; Advani, S; Burton, RE; Zhelev, DV; Needham, D; Simon, SA
MLA Citation
McIntosh, TJ, Advani, S, Burton, RE, Zhelev, DV, Needham, D, and Simon, SA. "Experimental tests for protrusion and undulation pressures in phospholipid bilayers." Biochemistry 34.27 (July 11, 1995): 8520-8532.
PMID
7612594
Source
pubmed
Published In
Biochemistry
Volume
34
Issue
27
Publish Date
1995
Start Page
8520
End Page
8532

Range and magnitude of the steric pressure between bilayers containing phospholipids with covalently attached poly(ethylene glycol).

The interactive properties of liposomes containing phospholipids with covalently attached poly(ethylene glycol) (PEG-lipids) are of interest because such liposomes are being developed as drug delivery vehicles and also are ideal model systems for measuring the properties of surface-grafted polymers. For bilayers containing PEG-lipids with PEG molecular weights of 350, 750, 2000, and 5000, pressure-distance relations have been measured by X-ray diffraction analysis of liposomes subjected to known applied osmotic pressures. The distance between apposing bilayers decreased monotonically with increasing applied pressure for each concentration of a given PEG-lipid. Although for bilayers containing PEG-350 and PEG-750 the contribution of electrostatic repulsion to interbilayer interactions was significant, for bilayers containing PEG-2000 and PEG-5000 the major repulsive pressure between bilayers was a steric pressure due to the attached PEG. The range and magnitude of this steric pressure increased both with increasing PEG-lipid concentration and PEG size, and the extension length of the PEG from the bilayer surface at maximum PEG-lipid concentration depended strongly on the size of the PEG, being less than 35 A for PEG-750, and about 65 A for PEG-2000 and 115 A for PEG-5000. The measured pressure-distance relations have been modeled in terms of current theories (deGennes, 1987; Milner et al., 1988b) for the steric pressure produced by surface-grafted polymers, as modified by us to take into account the effects of polymer polydispersity and the possibility that, at low grafting densities, polymers from apposing bilayers surfaces can interpenetrate or interdigitate. No one theoretical scheme is sufficient to account for all the experimental results. However, for a given pressure regime, PEG-lipid size, and PEG-lipid surface density, the appropriately modified theoretical treatment gives a reasonable fit to the pressure-distance data.

Authors
Kenworthy, AK; Hristova, K; Needham, D; McIntosh, TJ
MLA Citation
Kenworthy, AK, Hristova, K, Needham, D, and McIntosh, TJ. "Range and magnitude of the steric pressure between bilayers containing phospholipids with covalently attached poly(ethylene glycol)." Biophys J 68.5 (May 1995): 1921-1936.
PMID
7612834
Source
pubmed
Published In
Biophysical Journal
Volume
68
Issue
5
Publish Date
1995
Start Page
1921
End Page
1936
DOI
10.1016/S0006-3495(95)80369-3

Lysolipid exchange with lipid vesicle membranes.

While the aqueous solubility for bilayer phospholipids is less than 10(-10) M--keeping lipid membranes at essentially constant mass, single chain surfactants can have a significant aqueous solubility. Thus, in surfactant solutions, both monomer and micelles can interact with a lipid bilayer, and the mass and composition of the bilayer can be changed in seconds. These changes in composition are expected to have direct consequences on bilayer structure and material properties. We have found that the exchange of surfactants like lysolecithin can be described in terms of a kinetic model in which monomer and micelles are transported to the membrane from bulk solution. Molecular transport is considered at the membrane interfaces and across the midplane between the two monolayers of the bilayer. Using micropipet manipulation, single vesicles were transferred into lysolecithin solutions, and the measurement of vesicle area change gave a direct measure of lysolecithin uptake. Transfer back to lysolecithin-free media resulted in desorption. The rates of uptake and desorption could therefore be measured at controlled levels of membrane stress. With increasing lysolecithin concentration in the bulk phase, the amount of lysolecithin in the membrane reached saturation at approximately 3 mol% for concentrations below the critical micelle concentration (CMC) and at > 30 mol% for concentrations above the CMC. When convective transport was used to deliver lysolecithin, uptake occurred via a double exponential: initial uptake into the outer monolayer was fast (approximately 0.2 sec-1); transfer across the bilayer midplane was much slower (0.0019 sec-1).

Authors
Needham, D; Zhelev, DV
MLA Citation
Needham, D, and Zhelev, DV. "Lysolipid exchange with lipid vesicle membranes." Ann Biomed Eng 23.3 (May 1995): 287-298.
PMID
7631982
Source
pubmed
Published In
Annals of Biomedical Engineering
Volume
23
Issue
3
Publish Date
1995
Start Page
287
End Page
298

INFLUENCE OF BILAYER FLUCTUATIONS ON THE STERIC INTERACTIONS BETWEEN POLYMER-GRAFTED BILAYERS

Authors
HRISTOVA, K; NEEDHAM, D
MLA Citation
HRISTOVA, K, and NEEDHAM, D. "INFLUENCE OF BILAYER FLUCTUATIONS ON THE STERIC INTERACTIONS BETWEEN POLYMER-GRAFTED BILAYERS." LIQUID CRYSTALS 18.3 (March 1995): 423-430.
Source
wos-lite
Published In
Liquid Crystals
Volume
18
Issue
3
Publish Date
1995
Start Page
423
End Page
430
DOI
10.1080/02678299508036641

Centre theorem for two-dimensional complex holomorphic systems and its generalization

Authors
Needham, DJ
MLA Citation
Needham, DJ. "Centre theorem for two-dimensional complex holomorphic systems and its generalization." Proceedings of The Royal Society of London, Series A: Mathematical and Physical Sciences 450.1939 (1995): 225-232. (Academic Article)
Source
manual
Published In
Proceedings of The Royal Society of London, Series A: Mathematical and Physical Sciences
Volume
450
Issue
1939
Publish Date
1995
Start Page
225
End Page
232

Phase behavior of a lipid/polymer-lipid mixture in aqueous medium

The phase behavior of a mixture of bilayer forming lipids and polymer-lipids (lipids with covalently attached polymer to their hydrophilic moieties) in excess water is studied theoretically. The mixture is predicted to exhibit complex phase behavior for polymer molecular weights 2000 and 5000, depending on the concentration (fraction) of polymer-lipids in the lipid mixture. The bilayer is characterized by a maximal concentration nsat (saturation limit) of polymer-lipids that it can incorporate, as determined by its material properties (elastic modulus of area expansion and critical area expansion). At a different concentration ntr, which we call the thermodynamics crossover, micelle formation becomes energetically favorable over bilayer formation. We show that for DSPC and SOPC bilayers ntr < nsat. Increase of the polymer-lipid concentration above ntr leads to a gradual transition from a bilayer to a micellar phase; bilayers and micelles can coexist. In the transition region the polymer-lipid concentration is higher in the micellar phase than in the coexisting bilayer. © 1995 American Chemical Society.

Authors
Hristova, K; Needham, D
MLA Citation
Hristova, K, and Needham, D. "Phase behavior of a lipid/polymer-lipid mixture in aqueous medium." Macromolecules 28.4 (1995): 991-1002.
Source
scival
Published In
Macromolecules
Volume
28
Issue
4
Publish Date
1995
Start Page
991
End Page
1002

Lysolipid exchange with vesicle membranes and the formation and evolution of porous defects

Authors
Needham, D; Zhelev, DV
MLA Citation
Needham, D, and Zhelev, DV. "Lysolipid exchange with vesicle membranes and the formation and evolution of porous defects." Annals of Biomedical Engineering 23.3 (1995): 287-. (Academic Article)
Source
manual
Published In
Annals of Biomedical Engineering
Volume
23
Issue
3
Publish Date
1995
Start Page
287

The "Stealth" liposome: A prototypical biomaterial

Authors
Lasic, DD; Needham, D
MLA Citation
Lasic, DD, and Needham, D. "The "Stealth" liposome: A prototypical biomaterial." Chemical Reviews 95.8 (1995): 2601-2628.
Source
scival
Published In
Chemical Reviews
Volume
95
Issue
8
Publish Date
1995
Start Page
2601
End Page
2628

Adsorption and adhesion at vesicle surfaces: the influence of grafted polymer on avidin-biotin binding and tests of receptor-mediated adhesion

Micropipette techniques coupled to fluorescence video microscopy are used to carry out two kinds of experiments on adsorption and adhesion at vesicle surfaces. The model system of biotinylated lipid vesicles with avidin is also used. The binding of avidin to a single biotinylated vesicle is measured in the absence and presence of surface grafted polyethylene glycol. Likewise, adhesion energies are measured for two vesicles that are brought into adherent contact where adhesion results only from the formation of biotin-avidin-biotin cross-bridges.

Authors
Needham, D; Noppl, D
MLA Citation
Needham, D, and Noppl, D. "Adsorption and adhesion at vesicle surfaces: the influence of grafted polymer on avidin-biotin binding and tests of receptor-mediated adhesion." American Society of Mechanical Engineers, Bioengineering Division (Publication) BED 29 (1995): 331-332.
Source
scival
Published In
American Society of Mechanical Engineers, Bioengineering Division (Publication) BED
Volume
29
Publish Date
1995
Start Page
331
End Page
332

A novel micropipet method for measuring the bending modulus of vesicle membranes.

A theoretical model and an experiment are presented for determining the bending modulus of a bilayer vesicle membrane. The vesicle is held with a pipet having a radius between 1 and 2 microns, and the tension in the membrane is changed by changing the suction pressure. Then the vesicle membrane is deformed by aspirating it into a smaller pipet having a radius on the order of 0.5 microns. The relationship between the suction pressures in the two pipets is found to be linear, as predicted by the theoretical model. The curvature of the vesicle membrane at the pipet orifice and the bending modulus are found with the help of the model from the slope and the intercept of the linear experimental relationship between the suction pressures in the two pipets. The bending modulus for the two SOPC membranes studied in these experiments was found to be either 0.6 or 1.15 x 10(-19) J, which is similar to the values measured previously.

Authors
Zhelev, DV; Needham, D; Hochmuth, RM
MLA Citation
Zhelev, DV, Needham, D, and Hochmuth, RM. "A novel micropipet method for measuring the bending modulus of vesicle membranes." Biophys J 67.2 (August 1994): 720-727.
PMID
7948685
Source
pubmed
Published In
Biophysical Journal
Volume
67
Issue
2
Publish Date
1994
Start Page
720
End Page
727
DOI
10.1016/S0006-3495(94)80530-2

Role of the membrane cortex in neutrophil deformation in small pipets.

The simplest model for a neutrophil in its "passive" state views the cell as consisting of a liquid-like cytoplasmic region surrounded by a membrane. The cell surface is in a state of isotropic contraction, which causes the cell to assume a spherical shape. This contraction is characterized by the cortical tension. The cortical tension shows a weak area dilation dependence, and it determines the elastic properties of the cell for small curvature deformations. At high curvature deformations in small pipets (with internal radii less than 1 micron), the measured critical suction pressure for cell flow into the pipet is larger than its estimate from the law of Laplace. A model is proposed where the region consisting of the cytoplasm membrane and the underlying cortex (having a finite thickness) is introduced at the cell surface. The mechanical properties of this region are characterized by the apparent cortical tension (defined as a free contraction energy per unit area) and the apparent bending modulus (introduced as a bending free energy per unit area) of its middle plane. The model predicts that for small curvature deformations (in pipets having radii larger than 1.2 microns) the role of the cortical thickness and the resistance for bending of the membrane-cortex complex is negligible. For high curvature deformations, they lead to elevated suction pressures above the values predicted from the law of Laplace. The existence of elevated suction pressures for pipets with radii from 1 micron down to 0.24 micron is found experimentally. The measured excess suction pressures cannot be explained only by the modified law of Laplace (for a cortex with finite thickness and negligible bending resistance), because it predicts unacceptable high cortical thicknesses (from 0.3 to 0.7 micron). It is concluded that the membrane-cortex complex has an apparent bending modulus from 1 x 10(-18) to 2 x 10(-18) J for a cortex with a thickness from 0.1 micron down to values much smaller than the radius of the smallest pipet (0.24 micron) used in this study.

Authors
Zhelev, DV; Needham, D; Hochmuth, RM
MLA Citation
Zhelev, DV, Needham, D, and Hochmuth, RM. "Role of the membrane cortex in neutrophil deformation in small pipets." Biophys J 67.2 (August 1994): 696-705.
PMID
7948682
Source
pubmed
Published In
Biophysical Journal
Volume
67
Issue
2
Publish Date
1994
Start Page
696
End Page
705
DOI
10.1016/S0006-3495(94)80529-6

Increased adhesion between neutral lipid bilayers: interbilayer bridges formed by tannic acid.

Tannic acid (TA) is a naturally occurring polyphenolic compound that aggregates membranes and neutral phosolipid vesicles and precipitates many proteins. This study analyzes TA binding to lipid membranes and the ensuing aggregation. The optical density of dispersions of phosphatidylcholine (PC) vesicles increased upon the addition of TA and electron micrographs showed that TA caused the vesicles to aggregate and form stacks of tightly packed disks. Solution calorimetry showed that TA bound to PC bilayers with a molar binding enthalpy of -8.3 kcal/mol and zeta potential measurements revealed that TA imparted a small negative charge to PC vesicles. Monolayer studies showed that TA bound to PC with a dissociation constant of 1.5 microM and reduced the dipole potential by up to 250 mV. Both the increase in optical density and decrease in dipole potential produced by TA could be reversed by the addition of polyvinylpyrrolidone, a compound that chelates TA by providing H-bond acceptor groups. NMR, micropipette aspiration, and x-ray diffraction experiments showed that TA incorporated into liquid crystalline PC membranes, increasing the area per lipid molecule and decreasing the bilayer thickness by 2 to 4%. 2H-NMR quadrupole splitting measurements also showed that TA associated with a PC molecule for times much less than 10(-4) s. In gel phase bilayers, TA caused the hydrocarbon chains from apposing monolayers to fully interdigitate. X-ray diffraction measurements of both gel and liquid crystalline dispersions showed that TA, at a critical concentration of about 1 mM, reduced the fluid spacing between adjacent bilayers by 8-10 A. These data place severe constraints on how TA can pack between adjacent bilayers and cause vesicles to adhere. We conclude that TA promotes vesicle aggregation by reducing the fluid spacing between bilayers by the formation of transient interbilayer bridges by inserting its digallic acid residues into the interfacial regions of adjacent bilayers and spanning the interbilayer space.

Authors
Simon, SA; Disalvo, EA; Gawrisch, K; Borovyagin, V; Toone, E; Schiffman, SS; Needham, D; McIntosh, TJ
MLA Citation
Simon, SA, Disalvo, EA, Gawrisch, K, Borovyagin, V, Toone, E, Schiffman, SS, Needham, D, and McIntosh, TJ. "Increased adhesion between neutral lipid bilayers: interbilayer bridges formed by tannic acid." Biophys J 66.6 (June 1994): 1943-1958.
PMID
8075329
Source
pubmed
Published In
Biophysical Journal
Volume
66
Issue
6
Publish Date
1994
Start Page
1943
End Page
1958
DOI
10.1016/S0006-3495(94)80988-9

The Influence of Polymer-Grafted Lipids on the Physical Properties of Lipid Bilayers: A Theoretical Study

Experimental studies of bilayers containing polymer-grafted lipids have been underway for some time now (1-3). Modeling the physical properties of these bilayers, however, is not trivial because of the complexities in the self-assembling polymer-lipid/lipid bilayer system and the mutual influence of its two components: the lipid bilayer and the grafted polymer. In the paper we study the influence of the grafted polymer on the structural and interactive properties of the lipid bilayer. The modeling is done in terms of some existing polymer theories (de Gennes' scaling theory, Flory's and Milner's mean-field theories). We propose a simple lateral pressure model to calculate the critical concentration of polymer-lipid that can be incorporated into the bilayer. We study the influence of the polymer chains on the tensile strength of the bilayer and model the dependence of the elastic coefficients KA, kc, and k̄c on the concentration and molecular weight of the grafted polymer. For two bilayers in close proximity the interbilayer steric interactive forces are modeled for different polymer-lipid concentrations. © 1994 Academic Press. All rights reserved.

Authors
Hristova, K; Needham, D
MLA Citation
Hristova, K, and Needham, D. "The Influence of Polymer-Grafted Lipids on the Physical Properties of Lipid Bilayers: A Theoretical Study." Journal of Colloid And Interface Science 168.2 (1994): 302-314.
Source
scival
Published In
Journal of Colloid and Interface Science
Volume
168
Issue
2
Publish Date
1994
Start Page
302
End Page
314
DOI
10.1006/jcis.1994.1424

Measurement of material extravasation in microvascular networks using fluorescence video-microscopy.

We have developed a new method using fluorescence videomicroscopy to quantitate the extravasation of intravenously injected materials. This method can measure the relative plasma concentration of, and the vascular permeability to, these materials in microcirculatory preparations which contain multiple blood vessels in a field of view. The image of a tissue area containing multiple blood vessels is recorded via a SIT camera immediately before, and for an extended period after, the intravenous injection of a bolus of fluorescent test tracers. The videotape is analyzed off-line. At various time points, the light intensities of the entire tissue area and of several spots over selected vessels are measured. These measurements are then used to calculate the fluorescent light intensities arising from the tracers inside vessels (Iv) and in the interstitial region (Ii). Iv represents the relative amount of the tracers in the plasma, and Ii represents that in the interstitium. Iv and Ii are used to calculate an average permeability (P) for the vessels in the observed region. The benefit of this method is that it can be used to compare permeability of various tissues of interest or to serially evaluate changes in P in the same tissue over time. In this study, it was applied to measuring P to albumin as well as to liposomes in granulating and implanted tumor tissues in a rat skin flap window chamber. Changes in permeability to a small molecule (sulforhodamine B) before and during bradykinin application were also measured. The results of these experiments indicate that the relative plasma concentrations predicted by this method conformed well to those measured directly from blood samples, and the measured permeability values were consistent with previously published data. Therefore, this method provides a valid approach for quantitatively measuring the extravasation of intravenously injected molecular and colloidal materials in microcirculatory preparations. The method has a set of defined experimental conditions and assumptions that cannot be violated, however, or erroneous results can be obtained.

Authors
Wu, NZ; Klitzman, B; Rosner, G; Needham, D; Dewhirst, MW
MLA Citation
Wu, NZ, Klitzman, B, Rosner, G, Needham, D, and Dewhirst, MW. "Measurement of material extravasation in microvascular networks using fluorescence video-microscopy." Microvasc Res 46.2 (September 1993): 231-253.
PMID
8246821
Source
pubmed
Published In
Microvascular Research
Volume
46
Issue
2
Publish Date
1993
Start Page
231
End Page
253
DOI
10.1006/mvre.1993.1049

Increased microvascular permeability contributes to preferential accumulation of Stealth liposomes in tumor tissue.

Stealth liposomes have recently emerged as a promising antitumor drug delivery system, yet no studies have been reported to examine their dynamic behavior at the microcirculatory level. In this investigation, we have used in vivo fluorescence videomicroscopy to study the decay in plasma concentration and the interstitial accumulation of Stealth and conventional liposomes in tumor and granulating tissue microcirculatory preparations. Fluorescently labeled Stealth or conventional liposomes were injected i.v. into rats bearing dorsal skinflap window chambers, some of which contained a vascularized mammary adenocarcinoma. After injection, fluorescent light intensities arising from liposomes within blood vessels and the interstitium were measured over time. These measurements were used to derive plasma pharmacokinetics and vascular permeability coefficients for each liposome species in both tumor and granulating normal tissues. Within the first 90 min after injection, Stealth liposome accumulation in the tumor interstitium was 3-4-fold that for conventional liposomes. The percentage of administered liposomes remaining in the circulation at the end of 90 min was 60.2% for Stealth and 20.4% for conventional liposomes. Tumor vascular permeability was 3.42 +/- 0.78 x 10(-7)cm/s for Stealth and 1.75 x 0.38 x 10(-7)cm/s for conventional liposomes. In normal granulating tissues permeability for the 2 constructs was equivalent at 0.8-0.9 x 10(-7)cm/s. In conclusion, preferential accumulation of Stealth liposomes in tumors was attributable to a combination of slower plasma clearance and higher vascular permeability relative to conventional liposomes. Our method of combining in vivo microscopy with a tumor microcirculatory model provides a unique approach to study quantitatively the delivery of liposomes to tumor tissues, since it can be used to study the process in real time at the microcirculatory level.

Authors
Wu, NZ; Da, D; Rudoll, TL; Needham, D; Whorton, AR; Dewhirst, MW
MLA Citation
Wu, NZ, Da, D, Rudoll, TL, Needham, D, Whorton, AR, and Dewhirst, MW. "Increased microvascular permeability contributes to preferential accumulation of Stealth liposomes in tumor tissue." Cancer Res 53.16 (August 15, 1993): 3765-3770.
PMID
8339289
Source
pubmed
Published In
Cancer Research
Volume
53
Issue
16
Publish Date
1993
Start Page
3765
End Page
3770

Volume and osmotic properties of human neutrophils.

Quantitative models describing the dynamics of human neutrophils in the microcirculation require accurate morphometric parameters such as volume and surface membrane area. Using both a micropipette technique and video light microscopy (LM) to measure the diameters of the spherical cells, we have accurately determined the volume of the human neutrophil. Our value, 299 +/- 32 microns 3, is in good agreement with our earlier results, but 55% larger than that reported by Schmid-Schönbein et al (Blood 56:866, 1980). However, the measurements of Schmid-Schönbein et al were based on the actual mass of the cells derived from transmission electron microscopic (TEM) images. The membrane surface area, at lysis, was calculated to be 2.6 times its initial projected area. After lysis, the cells do not reduce their size, indicative of the possibility of a F-actin network formation that would stiffen the structure. Further, we show that neutrophils behave as ideal osmometers when exposed to anisotonic solutions at 21 degrees C, as predicted by the Boyle-Van't Hoff relationship. The calculated Ponder's value, R, is 0.77, which corresponds to 77% of the cell volume being osmotically active under isotonic conditions. However, at 37 degrees C, the cells are able to regulate their volumes toward the original volumes after an osmotic stress.

Authors
Ting-Beall, HP; Needham, D; Hochmuth, RM
MLA Citation
Ting-Beall, HP, Needham, D, and Hochmuth, RM. "Volume and osmotic properties of human neutrophils." Blood 81.10 (May 15, 1993): 2774-2780.
PMID
8490184
Source
pubmed
Published In
Blood
Volume
81
Issue
10
Publish Date
1993
Start Page
2774
End Page
2780

Viscosity of passive human neutrophils undergoing small deformations.

At issue is the type of constitutive equation that can be used to describe all possible types of deformation of the neutrophil. Here a neutrophil undergoing small deformations is studied by aspirating it into a glass pipet with a diameter that is only slightly smaller than the diameter of the spherically shaped cell. After being held in the pipet for at least seven seconds, the cell is rapidly expelled and allowed to recover its undeformed, spherical shape. The recovery takes approximately 15 s. An analysis of the recovery process that treats the cell as a simple Newtonian liquid drop with a constant cortical (surface) tension gives a value of 3.3 x 10(-5) cm/s for the ratio of the cortical tension to cytoplasmic viscosity. This value is about twice as large as a previously published value obtained with the same model from studies of large deformations of neutrophils. This discrepancy indicates that the cytoplasmic viscosity decreases as the amount of deformation decreases. An extrapolated value for the cytoplasmic viscosity at zero deformation is approximately 600 poise when a value for the cortical tension of 0.024 dyn/cm is assumed. Clearly the neutrophil does not behave like a simple Newtonian liquid drop in that small deformations are inherently different from large deformations. More complex models consisting either of two or more fluids or multiple shells must be developed. The complex structure inside the neutrophil is shown in scanning electron micrographs of osmotically burst cells and cells whose membrane has been dissolved away.

Authors
Hochmuth, RM; Ting-Beall, HP; Beaty, BB; Needham, D; Tran-Son-Tay, R
MLA Citation
Hochmuth, RM, Ting-Beall, HP, Beaty, BB, Needham, D, and Tran-Son-Tay, R. "Viscosity of passive human neutrophils undergoing small deformations." Biophys J 64.5 (May 1993): 1596-1601.
PMID
8324194
Source
pubmed
Published In
Biophysical Journal
Volume
64
Issue
5
Publish Date
1993
Start Page
1596
End Page
1601
DOI
10.1016/S0006-3495(93)81530-3

Tension-stabilized pores in giant vesicles: determination of pore size and pore line tension.

We present the first observations of giant, long-existing, stabilized pores in vesicle membranes. Using a new experimental technique for studying the electro-permeabilization of lipid membranes, giant liposomes (from 25 to 56 microns in diameter) were subjected to single, square, electric pulses (duration 150 microseconds and electric field strength from 63 to 126 kV/m). The liposomes were held by a micropipet and small membrane tensions were created by controlling the pipet suction pressure. The liposomes were loaded with media having different refractive index from the outside solution, and, under these conditions, the formation of pores in the pressurized liposome could be visualized by the jet of inside solution that flowed out from the membrane pore. By adjusting the membrane tension, pores were kept open, and pore lifetimes could be varied from tenths of a second to several seconds. The pore size was determined from the volumetric flow in the pore region and the measured pressure differences across the bilayer. It was clear from the experiments that only one pore remained opened after the pulse. The estimated pore radii were on the order of one micrometer. The pores were in a quasi-stationary state and when they closed they did so spontaneously in a quick process (in milliseconds). The isotropic membrane tension was determined for the same measurements and from determinations of both pore size and dynamic membrane tension the pore line tension was found. The line tension of the pore region was determined for two lipid compositions, stearoyl-oleoylphosphatidylcholine and stearoyl-oleoylphosphatidylcholine with 50 mol% cholesterol, and the obtained values for single bilayers were (0.92 +/- 0.07) x 10(-11) N and (3.05 +/- 0.12) x 10(-11) N, respectively.

Authors
Zhelev, DV; Needham, D
MLA Citation
Zhelev, DV, and Needham, D. "Tension-stabilized pores in giant vesicles: determination of pore size and pore line tension." Biochim Biophys Acta 1147.1 (April 8, 1993): 89-104.
PMID
8466935
Source
pubmed
Published In
Biochimica et Biophysica Acta: international journal of biochemistry and biophysics
Volume
1147
Issue
1
Publish Date
1993
Start Page
89
End Page
104

The effect of flunarizine on erythrocyte suspension viscosity under conditions of extreme hypoxia, low pH, and lactate treatment.

Flunarizine is a class IV calcium channel blocker which increases oxygen delivery to hypoxic regions in solid tumours, exerting a radiosensitising effect in vivo in animal tumour models. Precisely how the drug improves oxygenation is not well understood. We hypothesised that metabolic conditions present within solid tumours reduce red blood cell (RBC) deformability and that flunarizine exerts its in vivo effect by preventing this loss of RBC deformability. A microrheometer was used to compare the viscosity of rat and human RBC suspensions in conditions of hypoxia (pO2 < 10 mmHg), acidic environment (pH 6.8), and elevated lactate concentration (lactate 5 mMol l-1), without or with flunarizine at concentrations of 5, 10, and 50 mg l-1. The effects of flunarizine on RBC density and morphology were also recorded. Hypoxia, low pH, and lactate exposure together increased both human and rat RBC suspension viscosity. Flunarizine at concentrations of 5 and 10 mg l-1 prevented the increases in viscosity. The drug caused dose-dependent shifts toward lower cell density while inducing a characteristic cupped shape (stomatcytic morphology), suggesting a mechanism involving calmodulin inhibition. The results support the hypothesis that flunarizine improves tumour blood flow and oxygenation by enhancing flow properties of RBC's in solid tumours.

Authors
Kavanagh, BD; Coffey, BE; Needham, D; Hochmuth, RM; Dewhirst, MW
MLA Citation
Kavanagh, BD, Coffey, BE, Needham, D, Hochmuth, RM, and Dewhirst, MW. "The effect of flunarizine on erythrocyte suspension viscosity under conditions of extreme hypoxia, low pH, and lactate treatment." Br J Cancer 67.4 (April 1993): 734-741.
PMID
8471430
Source
pubmed
Published In
British Journal of Cancer
Volume
67
Issue
4
Publish Date
1993
Start Page
734
End Page
741

Measurement of interbilayer adhesion energies.

Authors
Needham, D
MLA Citation
Needham, D. "Measurement of interbilayer adhesion energies." Methods Enzymol 220 (1993): 111-129.
PMID
8350749
Source
pubmed
Published In
Methods in Enzymology
Volume
220
Publish Date
1993
Start Page
111
End Page
129

Pentoxifylline modulates deformability, F-actin content, and superoxide anion production of polymorphonuclear leukocytes from diabetic cats.

Capillary occlusion is an early event in the development of diabetic retinopathy, and white blood cells have recently been shown to be involved. We have shown previously that pentoxifylline improves deformability and decreases F-actin content of unstimulated polymorphonuclear leukocytes from normal human subjects. The purpose of this study was to determine if pentoxifylline would improve three properties of unstimulated polymorphonuclear leukocytes from diabetic cats. The measured parameters were mechanical (whole cell deformability), structural (F-actin content) and biochemical (rate of superoxide anion production). Chronic hyperglycemia was induced in three cats by partial pancreatectomy, and they were kept in poor glycemic control for at least 6 months prior to the study. Polymorphonuclear leukocytes were isolated and the entry time of individual passive cells was measured during aspiration into a 4-micron micropipette under constant suction pressure (-15 cmH2O). Deformability was defined as the inverse of the entry time. F-actin content of passive cells was measured by NBD-phallacidin labeling followed by flow cytometry. The rate of superoxide anion production was measured spectrophotometrically by superoxide dismutase-inhibitable cytochrome c reduction. Following incubation for 15 min with 0.1, 1.0 and 10.0 mM pentoxifylline, the average entry time of passive polymorphonuclear leukocytes was reduced from control by 11 +/- 5% (P = 0.045), 17 +/- 6% (P = 0.007), and 36 +/- 5% (P < 0.001), respectively. The F-actin content decreased by 0%, 4 +/- 0.6% (P < 0.001), and 10 +/- 3% (P < 0.001), respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Authors
Sonkin, PL; Freedman, SF; Needham, D; Rao, KM; Hatchell, DL
MLA Citation
Sonkin, PL, Freedman, SF, Needham, D, Rao, KM, and Hatchell, DL. "Pentoxifylline modulates deformability, F-actin content, and superoxide anion production of polymorphonuclear leukocytes from diabetic cats." Exp Eye Res 55.6 (December 1992): 831-838.
PMID
1336731
Source
pubmed
Published In
Experimental Eye Research
Volume
55
Issue
6
Publish Date
1992
Start Page
831
End Page
838

Repulsive interactions and mechanical stability of polymer-grafted lipid membranes.

Liposome membranes containing lipids with covalently attached poly(ethylene glycol) (PEG-lipid) are currently being developed as drug delivery systems. These, so called, 'Stealth' liposomes have a relatively long half life (approximately 1 day) in blood circulation and show an altered biodistribution in vivo. The extended lifetime appears to result from a steric stabilization of the liposome by the grafted polymer. In order to characterize the surface structures that promote steric stability in such polymer-grafted lipid bilayer systems, we have used X-ray diffraction to measure the structural organization and interbilayer repulsion for lipid/cholesterol (2:1) bilayers incorporating 4 mol% of a PEG-lipid in which the molecular weight of the PEG moiety was 1900 g/mol. At this concentration, applied pressure versus interbilayer distance relations showed that the grafted polymer moiety extended approximately 50 A from the lipid surface and gave rise to a strong, slowly decaying repulsive pressure between membranes that opposed their close approach. Also, the pressure vs. distance relations were only modestly altered by changing the ionic strength of the medium (1 mM NaCl and 100 mM NaCl). Therefore, even though the PEG-lipid headgroup bears a negative charge, the long range pressure cannot be due primarily to an electrostatic double layer pressure. Measurements of lipid bilayer elasticity using micropipet manipulation showed that PEG-lipid did not change the cohesive properties of lipid/cholesterol liposomes which was consistent with the X-ray structural data showing that the PEG-lipid did not change the normal structure of the bilayer interior. From these data we conclude that the repulsive barrier properties of lipid-grafted PEG polymer chains originate mainly from a steric pressure and that this simple polymer steric stabilization is the basis for the extended in vivo circulation times observed for polymer-grafted liposomes.

Authors
Needham, D; McIntosh, TJ; Lasic, DD
MLA Citation
Needham, D, McIntosh, TJ, and Lasic, DD. "Repulsive interactions and mechanical stability of polymer-grafted lipid membranes." Biochim Biophys Acta 1108.1 (July 8, 1992): 40-48.
PMID
1643080
Source
pubmed
Published In
Biochimica et Biophysica Acta: international journal of biochemistry and biophysics
Volume
1108
Issue
1
Publish Date
1992
Start Page
40
End Page
48

A sensitive measure of surface stress in the resting neutrophil.

The simplest parameterized model of the "passive" or "resting receptive" neutrophil views the cell as being composed of an outer cortex surrounding an essentially liquid-like highly viscous cytoplasm. This cortex has been measured to maintain a small persistent tension of approximately 0.035 dyn/cm (Evans and Yeung. 1989. Biophys. J. 56:151-160) and is responsible for recovering the spherical shape of the cell after large deformation. The origin of the cortical tension is at present unknown, but speculations are that it may be an active process related to the sensitivity of a given cell to external stimulation and the "passive-active" transition. In order to characterize further this feature of the neutrophil we have used a new micropipet manipulation method to give a sensitive measure of the surface stress as a function of the surface area dilation of the highly ruffled cellular membrane. In the experiment, a single cell is driven down a tapered pipet in a series equilibrium deformation positions. Each equilibrium position represents a balance between the stress in the membrane and the pressure drop across the cell. For most cells that seemed to be "passive," as judged by their spherical appearance and lack of pseudopod activity, area dilations of approximately 30% were accompanied by only a small increase in the membrane tension, indicative of a very small apparent elastic area expansion modulus (approximately 0.04 dyn/cm). Extrapolations back to zero area dilation gave a value for the tension in the resting membrane of 0.024 +/- 0.003 dyn/cm, in close agreement with earlier measures. A few cells showed virtually no change in cortical tension and fit the persistent cortical tension model of Evans and Yeung (1989. Biophys. J. 56:151-160). However, other cells that also appeared "passive," as judged by their spherical appearance, had membrane tensions that increased as the apparent surface area was increased. Thus, the postulated,persistent "cortical tension" does not appear to be a unique and constant parameter for all cells as the membrane area is dilated.This measurement of membrane tension could represent a sensitive indication of the first stages of cell activation and the"passive-active" transition.

Authors
Needham, D; Hochmuth, RM
MLA Citation
Needham, D, and Hochmuth, RM. "A sensitive measure of surface stress in the resting neutrophil." Biophys J 61.6 (June 1992): 1664-1670.
PMID
1617145
Source
pubmed
Published In
Biophysical Journal
Volume
61
Issue
6
Publish Date
1992
Start Page
1664
End Page
1670
DOI
10.1016/S0006-3495(92)81970-7

Modulation of the interbilayer hydration pressure by the addition of dipoles at the hydrocarbon/water interface.

The effects of the cholesterol analog 5 alpha-cholestan-3 beta-ol-6-one (6-ketocholestanol) on bilayer structure, bilayer cohesive properties, and interbilayer repulsive pressures have been studied by a combination of x-ray diffraction, pipette aspiration, and dipole potential experiments. It is found that 6-ketocholestanol, which has a similar structure to cholesterol except with a keto moiety at the 6 position of the B ring, has quite different effects than cholesterol on bilayer organization and cohesive properties. Unlike cholesterol, 6-ketocholestanol does not appreciably modify the thickness of liquid-crystalline egg phosphatidylcholine (EPC) bilayers, and causes a much smaller increase in bilayer compressibility modulus than does cholesterol. These data imply that 6-ketocholestanol has both its hydroxyl and keto moieties situated near the water-hydrocarbon interface, thus making its orientation in the bilayer different from cholesterol's. The addition of equimolar 6-ketocholestanol into EPC bilayers increases the magnitude, but not the decay length, of the exponentially decaying repulsive hydration pressure between adjacent bilayers. Incorporation of equimolar 6-ketocholestanol into EPC monolayers increases the dipole potential by approximately 300 mV. These data are consistent with our previous observation that the magnitude of the hydration pressure is proportional to the square of the dipole potential. These results mean that 6-ketocholestanol, despite its location in the bilayer hydrocarbon region, approximately 10 A from the physical edge of the bilayer, modifies the organization of interlamellar water. We argue that the incorporation of 6-ketocholestanol into EPC bilayers increases the hydration pressure, at least in part, by increasing the electric field strength in the polar head group region.

Authors
Simon, SA; McIntosh, TJ; Magid, AD; Needham, D
MLA Citation
Simon, SA, McIntosh, TJ, Magid, AD, and Needham, D. "Modulation of the interbilayer hydration pressure by the addition of dipoles at the hydrocarbon/water interface." Biophys J 61.3 (March 1992): 786-799.
PMID
1504249
Source
pubmed
Published In
Biophysical Journal
Volume
61
Issue
3
Publish Date
1992
Start Page
786
End Page
799
DOI
10.1016/S0006-3495(92)81883-0

Structure and cohesive properties of sphingomyelin/cholesterol bilayers.

Thermal, structural, and cohesive measurements have been obtained for both bovine brain sphingomyelin (BSM) and N-tetracosanoylsphingomyelin (C24-SM) in the presence and absence of cholesterol. A goal of these experiments has been to clarify the mechanisms responsible for the strong interaction between sphingomyelin and cholesterol. Differential scanning calorimetry shows that fully hydrated bilayers of BSM and C24-SM have main endothermic phase transitions at 39 and 46 degrees C, respectively, that reflect the melting of the acyl chains from a gel to a liquid-crystalline phase. For each lipid, the addition of cholesterol monotonically reduces the enthalpy of this transition, so that at equimolar cholesterol the transition enthalpy is zero. The addition of equimolar cholesterol to either BSM or C24-SM coverts the wide-angle X-ray diffraction reflection at 4.15 A to a broad band centered at 4.5 A. Electron density profiles of gel-phase C24-SM bilayers contain two terminal methyl dips in the center of the bilayer, indicating that the lipid hydrocarbon chains partially interdigitate so that the long saturated 24-carbon acyl chains in one monolayer cross the bilayer center and appose the shorter sphingosine chains from the other monolayer. The incorporation of cholesterol adds electron density to the hydrocarbon chain region near the head group and removes the double terminal methyl dip. These wide- and low-angle X-ray data indicate that cholesterol packs into the hydrocarbon chain region near the sphingomyelin head group, fluidizes the methylene chains near the center of the bilayer compared to the gel phase, and reduces the extent of methylene chain interdigitation.(ABSTRACT TRUNCATED AT 250 WORDS)

Authors
McIntosh, TJ; Simon, SA; Needham, D; Huang, CH
MLA Citation
McIntosh, TJ, Simon, SA, Needham, D, and Huang, CH. "Structure and cohesive properties of sphingomyelin/cholesterol bilayers." Biochemistry 31.7 (February 25, 1992): 2012-2020.
PMID
1536844
Source
pubmed
Published In
Biochemistry
Volume
31
Issue
7
Publish Date
1992
Start Page
2012
End Page
2020

Interbilayer interactions between sphingomyelin and sphingomyelin/cholesterol bilayers.

Pressure versus fluid spacing relations have been obtained for sphingomyelin bilayers in the gel phase and equimolar sphingomyelin/cholesterol in the liquid-crystalline phase by the use of X-ray diffraction analysis of osmotically stressed aqueous dispersions and oriented multilayers. For interbilayer separations in the range of 5-20 A, the repulsive hydration pressure decays exponentially with increasing fluid spacing. The decay length (lambda) of this repulsive pressure is about 2 A for both bovine brain and N-tetracosanoylsphingomyelin, similar to that previously found for phosphatidylcholine bilayers. However, both the magnitude of the hydration pressure and the magnitude of the dipole potential (V) measured for monolayers in equilibrium with liposomes are considerably smaller for sphingomyelin than for either gel or liquid-crystalline phosphatidylcholine bilayers. Addition of equimolar cholesterol increases both the magnitude of the hydration pressure and the dipole potential. These data suggest that the magnitude of the hydration pressure depends on the electric field at the interface as given by (V/lambda)2. For sphingomyelin bilayers, there is a sharp upward break in the pressure-fluid spacing relation at an interbilayer spacing of about 5 A, indicating the onset of steric hindrance between the head groups of apposing bilayers.

Authors
McIntosh, TJ; Simon, SA; Needham, D; Huang, CH
MLA Citation
McIntosh, TJ, Simon, SA, Needham, D, and Huang, CH. "Interbilayer interactions between sphingomyelin and sphingomyelin/cholesterol bilayers." Biochemistry 31.7 (February 25, 1992): 2020-2024.
PMID
1536845
Source
pubmed
Published In
Biochemistry
Volume
31
Issue
7
Publish Date
1992
Start Page
2020
End Page
2024

Formal theory concerning the generation and propagation of travelling wave-fronts in reaction-diffusion equations

In this paper we develop a formal approach to examining the long-time asymptotic form of propagating wave-fronts which can develop in initial boundary-value problems for partial differential equations of the reaction-diffusion type. Particular attention is given to the long-time asymptotic wave-front propagation speed.

Authors
Needham, DJ
MLA Citation
Needham, DJ. "Formal theory concerning the generation and propagation of travelling wave-fronts in reaction-diffusion equations." Quarterly Journal of Mechanics and Applied Mathematics 45.pt 3 (1992): 469-498. (Academic Article)
Source
manual
Published In
Quarterly Journal of Mechanics and Applied Mathematics
Volume
45
Issue
pt 3
Publish Date
1992
Start Page
469
End Page
498

Polymer-grafted liposomes: Physical basis for the 'Stealth' property

Polymer-bearing lipids have recently been incorporated into liposomes that are used in in vivo drug delivery. This strategy has improved the liposome's ability to avoid the reticuloendothelial system and has thereby increased its circulation time in the bloodstream. In order to understand the physical basis for this so called Stealth® effect, we have begun a series of studies that characterize the surface structure, interactive properties and in vivo performance of the polymer-bearing, Stealth lipids. For a 1900 g/mol polyethylene glycol (PEG) moiety, we have used x-ray diffraction and micropipet manipulation methods to show that, (i) the polymer chains extend ~50Å out from the lipid bilayer surface; (ii) this surface polymer exerts a significant long range mutual repulsion between adjacent bilayers that prevents bilayer-bilayer adhesion. Furthermore, the measured polymer extension and repulsive pressure are well modelled by polymer scaling laws. These results imply that the interaction of macromolecules and cellular surfaces with the Stealth liposome is probably limited to a distance of ~50Å from the liposome surface. We conclude that the origin of the Stealth effect lies in a steric stabilization mechanism. By using fluorescence video microscopy to observe implanted tumor tissue, we have also shown that fluorescent Stealth liposomes extravasate through the leaky vessel walls of tumors. This method allows us to characterize in real time the accumulation of liposomes and release of drug at an implanted tumor site.

Authors
Needham, D; Hristova, K; McIntosh, TJ; Dewhirst, M; Wu, N; Lasic, DD; Alving, CR; Wassef, NM; Senior, JH; Ghosh, PC; Bachhawat, BK; Allen, TM
MLA Citation
Needham, D, Hristova, K, McIntosh, TJ, Dewhirst, M, Wu, N, Lasic, DD, Alving, CR, Wassef, NM, Senior, JH, Ghosh, PC, Bachhawat, BK, and Allen, TM. "Polymer-grafted liposomes: Physical basis for the 'Stealth' property." Journal of Liposome Research 2.3 (1992): 411-430.
Source
scival
Published In
Journal of Liposome Research
Volume
2
Issue
3
Publish Date
1992
Start Page
411
End Page
430

A physical characterization of GAP A3 hybridoma cells: morphology, geometry, and mechanical properties.

Morphological, geometrical, and rheological properties of the GAP A3 hybridoma cell line have been evaluated as a function of the cell cycle. Interference contrast video microscopy and scanning electron microscopy (SEM) showed that a sample of cells taken from the middle of the exponential growth phase displayed a range of cell morphologies, consistent with a heterogeneous growing culture. Micropipet manipulation was used to measure the geometrical (cell volume) and mechanical (cortical tension and apparent cell viscosity) properties of single cells selected at random from a sample in the middle of the exponential growth phase. Consistent with the range of morphologies, cell volumes (1400 to 5700 microm(3)) and apparent viscosities (430 to 1.2 x 10(4) P) showed a wide range of values at 37 degrees C, demonstrating that a hybridoma cell line cannot be characterized by a single value for any one property, and that properties must be related to their cycle dependence when considering proliferating cells. Direct, video-microscopic observation of synchronized cells, and of individual cells that were followed throughout their cell cycle, allowed us to correlated distinct morphologies with phases of the cell cycle. As the cell cycle progresses, an increase in cell volume by a factor of 3 to 4 is accompanied by an overall increase in apparent cell viscosity by approximately the same ratio, consistent with an accumulation of more cytoplasmic material in the older cells. Also, a decrease in average apparent viscosity by a factor of 10. These results are important in order to evaluate the possible role of certain structural, cell-cycle dependent features in shear and abrasion sensitivity. This is a problem of current concern in the bioreactor culture of mammalian cells.

Authors
Needham, D; Ting-Beall, HP; Tran-Son-Tay, R
MLA Citation
Needham, D, Ting-Beall, HP, and Tran-Son-Tay, R. "A physical characterization of GAP A3 hybridoma cells: morphology, geometry, and mechanical properties." Biotechnol Bioeng 38.8 (October 20, 1991): 838-852.
PMID
18600841
Source
pubmed
Published In
Biotechnology & Bioengineering
Volume
38
Issue
8
Publish Date
1991
Start Page
838
End Page
852
DOI
10.1002/bit.260380806

Time-dependent recovery of passive neutrophils after large deformation.

Experiments are performed in which a passive human neutrophil is deformed into an elongated "sausage" shape by aspirating it into a small glass pipette. When expelled from the pipette the neutrophil recovers its natural spherical shape in approximately 1 minute. This recovery process is analyzed according to a Newtonian, liquid-drop model in which a variational method is used to simultaneously solve the hydrodynamic equations for low Reynolds-number flow and the equations for membrane equilibrium with a constant membrane tension. The theoretical model gives a good fit to the experimental data for a ratio of membrane cortical tension to cytoplasmic viscosity of approximately 1.7 x 10(-5) cm/s (0.17 micron/s). However, when the cell is held in the pipette for only a short time period of 5 s or less, and then expelled, the cell undergoes an initial, rapid elastic rebound suggesting that the cell behaves in this instance as a Maxwell viscoelastic liquid rather than a Newtonian liquid with constant cortical tension.

Authors
Tran-Son-Tay, R; Needham, D; Yeung, A; Hochmuth, RM
MLA Citation
Tran-Son-Tay, R, Needham, D, Yeung, A, and Hochmuth, RM. "Time-dependent recovery of passive neutrophils after large deformation." Biophys J 60.4 (October 1991): 856-866.
PMID
1742456
Source
pubmed
Published In
Biophysical Journal
Volume
60
Issue
4
Publish Date
1991
Start Page
856
End Page
866
DOI
10.1016/S0006-3495(91)82119-1

Possible role of cell cycle-dependent morphology, geometry, and mechanical properties in tumor cell metastasis.

Studies that examine the shear- and abrasion-sensitivity of proliferating cells are important in order to understand the behavior of hybridoma cells in bioreactor culture and metastasizing cancer cells in the bloodstream. Little is known about the link between morphology, structure, and mechanical properties of a given cell line, especially with respect to variations throughout the cell cycle. In our experiments with GAP A3 hybridoma cells, distinct cell morphologies were identified and correlated with phases of the cell cycle by video microscopic observation of synchronized cells, and of individual cells that were followed throughout their cell cycle. Micropipet manipulation was used to measure the geometrical (cell volume) and mechanical (apparent cell viscosity) properties of single cells. As the cell cycle progressed at 37 degrees C, an increase in cell volume from 1400 microns 3 to 5700 microns 3 was accompanied by an increase in apparent cell viscosity from 430 poise to 12,000 poise, consistent with an accumulation of more cytoplasmic material in the "older" cells. Hybridomas are representative of the various leukemias derived from hemopoietic cells, and even though as a whole, they appeared to be rather shear-insensitive, the wide range of property values demonstrates that a given cell line cannot be characterized by a single value for any one property, and that properties must be related to the cell cycle when considering proliferating cells. It is interesting to see if distinct stages in the metastatic sequence of events might correlate with any of these physical features of the cell cycle, irrespective of cell type or cell line. For example, the cytokinetic doublet could represent a fragile structure that may fail and produce cell death under fluid-shear conditions that would not affect the cells at any other stage in the cell cycle. Identifying such cell cycle-dependent features in metastasizing cancer cells could lead to a better understanding of the metastatic process and to possible clinical treatments directed at making cells more shear- and abrasion-sensitive, and therefore, more likely to be killed by the natural hydrodynamic forces of the circulatory system.

Authors
Needham, D
MLA Citation
Needham, D. "Possible role of cell cycle-dependent morphology, geometry, and mechanical properties in tumor cell metastasis." Cell Biophys 18.2 (April 1991): 99-121. (Review)
PMID
1726529
Source
pubmed
Published In
Cell Biophysics
Volume
18
Issue
2
Publish Date
1991
Start Page
99
End Page
121

Morphology, geometry and mechanical properties of GAP A3 hybridoma cells as a function of the cell cycle

The sensitivity of animal cells in bioreactor culture to hydrodynamic shear and abrasion results in reduced cell growth rate and viability and is widely perceived as a barrier to scale-up in processing. Cell shear- and abrasion-sensitivity is also important in determining the behavior of proliferating cells in other hydrodynamic environments such as metastasizing cancer cells in the blood stream. Little is known about the link between morphology, structure and mechanical properties of a given cell line, especially with respect to variations throughout the cell cycle. In our experiments, distinct hybridoma cell morphologies were identified and correlated with phases of the cell cycle by video microscopic observation of synchronized cells, and of individual cells that were followed throughout their cell cycle. Micropipet manipulation was used to measure the geometrical (cell volume) and mechanical (apparent cell viscosity) properties of single cells. As the cell cycle progressed, an increase in cell volume from 1400 μm3 to 5700 μm3 was accompanied by an increase in apparent cell viscosity from 430 poise to 12,000 poise, consistent with an accumulation of more cytoplasmic material in the older cells. Hybridomas are representative of the various leukemias derived from hemopoietic cells and even though they appeared to be rather shear-insensitive, the wide range of property values demonstrates that a given cell line cannot be characterized by a single value for any one property, and that properties must be related to the cell cycle when considering proliferating cells. Identifying such cell cycle dependent features in metastasizing cancer cells could lead to clinical treatments directed at making them more shear- and abrasion-sensitive and therefore more likely to be killed by the natural hydrodynamic forces of the circulatory system.

Authors
Needham, D
MLA Citation
Needham, D. "Morphology, geometry and mechanical properties of GAP A3 hybridoma cells as a function of the cell cycle." Annals of Biomedical Engineering 19.5 (1991): 592-593.
Source
scival
Published In
Annals of Biomedical Engineering
Volume
19
Issue
5
Publish Date
1991
Start Page
592
End Page
593

Mechanical and interactive properties of lipid membranes containing surface-bound polymer

The rapid clearance, from the blood stream, of liposomes used in delivery systems is one of the major obstacles to advancing many applications of liposomes in medical technologies. The incorporation of glycolipids or a lipid that contains a large polymeric polar headgroup into the liposomes greatly enhances the circulation time of the injected dose in the blood. As a first step in understanding the physical mechanisms(s) operating in these processes, we have carried out a characterization of the mechanical and interactive properties of lipid bilayer systems of typical liposome formulations containing phospholipids, cholesterol, GMl and a polyethylene oxide lipid (PEOL). (Liposome Technology, Inc.). A micropipet manipulation method was used to determine the elastic area expansion modulus K, and several failure parameters of individual lipid vesicles. The repulsive, mutual interaction between lipid bilayers was examined by an x-ray method that measured the interbilayer gap separation as a function of applied pressure and also gave an indication of polymer-polymer interactions in the gap from electron density profiles. Compared to the hydrated lipid membrane, the inclusion of GMl and PEOL greatly increased the interbilayer separation distance, with the polymer producing the largest effect. In a low pressure regime, the exponential decay constant was -8 to 10 A for both surface groups, before a stiffer repulsive interaction appeared at high pressure and close separation. Even though the precise mechanism of action is not yet known, it is clear that the presence of surface bound moieties act to increase repulsive interactions and may also inhibit opsonization of the liposomes, thereby evading identification to the RES.

Authors
Needham, D; McIntosh, TJ
MLA Citation
Needham, D, and McIntosh, TJ. "Mechanical and interactive properties of lipid membranes containing surface-bound polymer." Annals of Biomedical Engineering 19.5 (1991): 593--.
Source
scival
Published In
Annals of Biomedical Engineering
Volume
19
Issue
5
Publish Date
1991
Start Page
593-

Deformation and flow of neutrophils and monocytes

The deformation and flow of neutrophils and monocytes in the smallest vessels is studied experimentally. The preparation of cells, micropipet manipulation, measurement of cortical tension, measurement of viscosity and of the rate of recovery is described. It is concluded that neutrophils and monocytes behave more like a liquid than a solid. However. it is a simplification to say that these cells behave like a Newtonian liquid drop with a constant cortical tension. The cell's complex cytoplasmic fluid has a distionctly non-Newtonian character. It responds elastically when deformed rapidly, but its elastic memory fades quickly - in less than 5 seconds. The behavior of the neutrophil as a Maxwell liquid may account for its shear-thinning behavior. The cortical tension also may change as the cell is deformed.

Authors
Hochmuth, RM; Needham, D; Ting-Beall, HP
MLA Citation
Hochmuth, RM, Needham, D, and Ting-Beall, HP. "Deformation and flow of neutrophils and monocytes." American Society of Mechanical Engineers, Bioengineering Division (Publication) BED 20 (1991): 417-419.
Source
scival
Published In
American Society of Mechanical Engineers, Bioengineering Division (Publication) BED
Volume
20
Publish Date
1991
Start Page
417
End Page
419

Recovery of passive neutrophils after large deformation. Liquid drop model

The validity of the Neutonian liquid model as a description of the recovery of a neutrophil after large deformation is investigated. In the first part, we report the results of experiments in which cells are deformed from their resting spherical geometry, then released from this state and their progress of recovery is monitored. Holding times in the deformed state, before recovery is allowed to proceed, range from tenths of a second to tens of seconds. In the second part, a theoretical model for the recovery, after large deformation, of Newtonian liquid drops is presented.

Authors
Tran-Son-Tay, R; Needham, D; Hochmuth, RM
MLA Citation
Tran-Son-Tay, R, Needham, D, and Hochmuth, RM. "Recovery of passive neutrophils after large deformation. Liquid drop model." American Society of Mechanical Engineers, Bioengineering Division (Publication) BED 20 (1991): 421-424.
Source
scival
Published In
American Society of Mechanical Engineers, Bioengineering Division (Publication) BED
Volume
20
Publish Date
1991
Start Page
421
End Page
424

Deformation and flow of neutrophils in micropipets

The undeformed human neutrophil in the resting, passive state is shaped like a sphere with a diamter of about 8 μm. Thus, it must deform significantly in order to flow through the small capillaries (approximately 4 μm) of the body. To model and understand this process we study the deformation and flow of neutrophils into uniform and tapered glass pipers with pipet openings on the order of 4 μm. We find, as others have, that the passive neutrophil does not behave as a 'standard solid' but instead deforms and flows smoothly like a liquid drop. This liquid drop has a persistent 'surface' tension that is very small - about 0.02-0.04 dyn/cm. In some instances the tension appears to increase as the surface area of the cell is expanded. The apparent viscosity of this liquid drop is very large - about 103 poise - and appears to decrease somewhat at higher rates of flow. For slow flows over long periods of time the cell can 'activate' without sticking to the pipet wall and without forming pseudopods. In these instances the cell behaves as a viscoelastic gel with a much larger resistance to deformation and flow than that exhibited by a resting cell.

Authors
Hochmuth, RM; Needham, D; Ting-Beall, HP; Zhelev, D
MLA Citation
Hochmuth, RM, Needham, D, Ting-Beall, HP, and Zhelev, D. "Deformation and flow of neutrophils in micropipets." Annals of Biomedical Engineering 19.5 (1991): 568--.
Source
scival
Published In
Annals of Biomedical Engineering
Volume
19
Issue
5
Publish Date
1991
Start Page
568-

Elastic deformation and failure of lipid bilayer membranes containing cholesterol.

Giant bilayer vesicles were reconstituted from several lipids and lipid/cholesterol (CHOL) mixtures: stearolyloleoylphosphatidylcholine (SOPC), bovine sphingomyelin (BSM), diarachidonylphosphatidylcholine (DAPC), SOPC/CHOL, BSM/CHOL, DAPC/CHOL, and extracted red blood cell (RBC) lipids with native cholesterol. Single-walled vesicles were manipulated by micropipette suction and several membrane material properties were determined. The properties measured were the elastic area compressibility modulus K, the critical areal strain alpha c, and the tensile strength tau lys, from which the failure energy or membrane toughness Tf was calculated. The elastic area expansion moduli for these lipid and lipid/cholesterol bilayers ranged from 57 dyn/cm for DAPC to 1,734 dyn/cm for BSM/CHOL. The SOPC/CHOL series and RBC lipids had intermediate values. The results indicated that the presence of cholesterol is the single most influential factor in increasing bilayer cohesion, but only for lipids where both chains are saturated, or mono- or diunsaturated. Multiple unsaturation in both lipid chains inhibits the condensing effect of cholesterol in bilayers. The SOPC/CHOL system was studied in more detail. The area expansion modulus showed a nonlinear increase with increasing cholesterol concentration up to a constant plateau, indicating a saturation limit for cholesterol in the bilayer phase of approximately 55 mol% CHOL. The membrane compressibility was modeled by a property-averaging composite theory involving two bilayer components, namely, uncomplexed lipid and a lipid/cholesterol complex of stoichiometry 1/1.22. The area expansion modulus of this molecular composite membrane was evaluated by a combination of the expansion moduli of each component scaled by their area fractions in the bilayer. Bilayer toughness, which is the energy stored in the bilayer at failure, showed a maximum value at approximately 40 mol% CHOL. This breakdown energy was found to be only a fraction of the available thermal energy, implying that many molecules (approximately 50-100) may be involved in forming the defect structure that leads to failure. The area expansion modulus of extracted RBC lipids with native cholesterol was compared with recent measurements of intact RBC membrane compressibility. The natural membrane was also modeled as a simple composite made up to a compressible lipid/cholesterol matrix containing relatively incompressible transmembrane proteins. It appears that the interaction of incompressible proteins with surrounding lipid confers enhanced compressibility on the composite structure.

Authors
Needham, D; Nunn, RS
MLA Citation
Needham, D, and Nunn, RS. "Elastic deformation and failure of lipid bilayer membranes containing cholesterol." Biophys J 58.4 (October 1990): 997-1009.
PMID
2249000
Source
pubmed
Published In
Biophysical Journal
Volume
58
Issue
4
Publish Date
1990
Start Page
997
End Page
1009
DOI
10.1016/S0006-3495(90)82444-9

Rapid flow of passive neutrophils into a 4 microns pipet and measurement of cytoplasmic viscosity.

Neutrophils from five different individuals are isolated with a density separation technique. A total of 151 unactivated (passive) cells are rapidly aspirated at constant suction pressure and at room temperature into a pipet with a diameter of 4 microns. The suction pressures in excess of an initial yield threshold are 0.5, 1 and 2 kPa and are comparable to those encountered in the microcirculation. These pressures are well in excess of the small suction pressure of approximately 20 Pa that is required to form a static hemispherical bump on the cell. At a given aspiration pressure, the leading edge of an individual cell is "tracked" as it flows into the pipet. A theory based on the flow of a Newtonian liquid from either a hemisphere or a spherical segment into a cylinder is used to model the entry process. Both theory and experiment show that during most of the entry process the leading edge of the cell moves at a nearly constant velocity with a rapid acceleration at the end. For cells from five different individuals at the three different excess aspiration pressures, Newtonian theory gives a cytoplasmic viscosity of 135 +/- 54 Pa.s and overall entry times of 3.3s (0.5 kPa), 1.6s (1 kPa) and 0.82s (2 kPa). These results and those of Evans and Yeung at lower aspiration pressures indicate that the complex cytoplasm inside unactivated neutrophils behaves as a nearly Newtonian fluid with a viscosity on the order of 10(2) Pa.s over almost a two order of magnitude range in aspiration pressure and, thus, rate of deformation.

Authors
Needham, D; Hochmuth, RM
MLA Citation
Needham, D, and Hochmuth, RM. "Rapid flow of passive neutrophils into a 4 microns pipet and measurement of cytoplasmic viscosity." J Biomech Eng 112.3 (August 1990): 269-276.
PMID
2214708
Source
pubmed
Published In
Journal of Biomechanical Engineering
Volume
112
Issue
3
Publish Date
1990
Start Page
269
End Page
276

Effect of pentoxifylline on the flow of polymorphonuclear leukocytes through a model capillary.

Pentoxifylline is a methylxanthine derivative used to increase blood flow in peripheral atherosclerosis. Pentoxifylline is known to increase whole blood filtration rate, and recent evidence suggests that pentoxifylline increases the filtration rate of polymorphonuclear leukocytes (PMNs). The purpose of this study was to directly observe and quantitate the effect of pentoxifylline on the flow of individual PMNs into a model capillary. Short-term incubation of human PMNs with 10 mM pentoxifylline inhibited cell activation, as judged by a significant reduction in the number of neutrophils forming pseudopods. Furthermore, incubation of PMNs from 6 healthy men with 0.1, 1.0 and 10 mM pentoxifylline significantly decreased the time required for individual cells to be aspirated into a 4 microns pipet under constant pressure by 16 +/- 5%, 21 +/- 7%, and 41 +/- 8%, respectively (mean +/- SEM, p less than or equal to 0.05), compared with control. These experiments are the first direct demonstration of increased deformability in neutrophils treated with pentoxifylline. The results are consistent with the hypothesis that the beneficial effect of pentoxifylline on microvascular perfusion is partly due to an inhibition of PMN stiffness and activation.

Authors
Armstrong, M; Needham, D; Hatchell, DL; Nunn, RS
MLA Citation
Armstrong, M, Needham, D, Hatchell, DL, and Nunn, RS. "Effect of pentoxifylline on the flow of polymorphonuclear leukocytes through a model capillary." Angiology 41.4 (April 1990): 253-262.
PMID
2339824
Source
pubmed
Published In
Angiology
Volume
41
Issue
4
Publish Date
1990
Start Page
253
End Page
262
DOI
10.1177/000331979004100401

Morphology and mechanical properties of gap A3 hybridoma cells as related to cell cycle

The morphological and rheological properties of a hybridoma cell line namely, GAP A3, have been evaluated as a function of its cell cycle. Results show that a hybridoma cell line cannot be characterized by a single value for any one property, and that properties must be related to their cell cycle dependence when considering proliferating cells. It is found that as the cell cycle progresses, an increase in cell volume by a factor of 3 to 4 is accompanied by an overall increase in cell viscosity by approximately the same ratio, consistent with an accumulation of more cytoplasmic material in the older cells. Interestingly, cytoplasmic reorganization in preparation for mitosis resulted in a slight reduction in viscosity. Cell viscosity also showed some temperature dependence. A decrease in temperature from 37°C to 14°C was accompanied by an increase in average cell viscosity by a factor of 10. SEM showed that although most cells were blebbed, cells only displayed microvilli on their surfaces in mitosis and throughout cytokinesis, and that this excess membrane was rapidly recovered by the resulting daughter cells. These results are important in order to evaluate the possible role of certain structural, cell cycle dependent, features in shear and abrasion sensitivity. This is a problem of current concern in the bioreactor culture of mammalian cells.

Authors
Needham, D; Ting-Beall, HP; Tran-Son-Tay, R
MLA Citation
Needham, D, Ting-Beall, HP, and Tran-Son-Tay, R. "Morphology and mechanical properties of gap A3 hybridoma cells as related to cell cycle." American Society of Mechanical Engineers, Bioengineering Division (Publication) BED 16 (1990): 5-10.
Source
scival
Published In
American Society of Mechanical Engineers, Bioengineering Division (Publication) BED
Volume
16
Publish Date
1990
Start Page
5
End Page
10

The viscosity of neutrophils and their transit times through small pores.

Passive neutrophils from five different individuals are rapidly aspirated at constant suction pressure and at room temperature into a pipet with a diameter of 4 microns. The excess suction pressures (i.e., the pressures in excess of the small threshold pressure required to produce continuous flow into the pipet) are 5000, 10,000 and 20,000 dyn/cm2 (0.5, 1 and 2 kPa) and are comparable to those encountered in the microcirculation. The rate of entry into the pipet is modeled with a linearized version of a theory by Yeung and Evans for the newtonian flow of a neutrophil into a pipet or pore. From this theory and measurements of the cell size and its rate of entry into the pipet, we can calculate a value for the cytoplasmic viscosity. A linear (newtonian) fit of the theory to the experimental data gives a value for the viscosity of 1050 poise. A non-linear fit predicts a decrease in the "apparent viscosity" from about 1500 poise at zero excess pressure to 1000 poise at an excess aspiration pressure of 20,000 dyn/cm2. Our experiments and analysis also allow us to calculate a value for the transit time through short pores over a wide range of excess aspiration pressures and pore diameters. For example, for a pore diameter of 3 microns and an aspiration pressure of 1250 dyn/cm2, we predict a transit time of about 70 s. At 6 microns and 20,000 dyn/cm2, the predicted transit time is only about 0.04 s.

Authors
Hochmuth, RM; Needham, D
MLA Citation
Hochmuth, RM, and Needham, D. "The viscosity of neutrophils and their transit times through small pores." Biorheology 27.6 (1990): 817-828.
PMID
2093391
Source
pubmed
Published In
Biorheology
Volume
27
Issue
6
Publish Date
1990
Start Page
817
End Page
828

Rapid deformation of "passive" polymorphonuclear leukocytes: the effects of pentoxifylline.

Entry times for spherical (no pseudopods) polymorphonuclear leukocytes (PMNs) into a 4 microns micropipet have been measured as a function of pipet suction pressure (2,500-20,000 dyn/cm2) and concentration of the drug pentoxifylline (PTX, 0.1-10.0 mM). For control cells (0 mM PTX), entry rates (reciprocal entry times) increased almost linearly with increasing suction pressure, indicating a Newtonian-like behavior. With incubation in PTX solutions, entry rate vs. suction pressure became increasingly non-linear, suggesting a shear-thinning effect for the dissipative structure. At a given suction pressure the rate of entry showed a dose-dependent increase with increasing PTX concentration, the effect being most pronounced at high suction pressures (20,000 dyn/cm2). Also, with increasing PTX concentration two other effects were observed: i) there was a decreased incidence of cells that displayed pseudopodia, and ii) there was an increased incidence of cells forming hernias and an increased streaming of cell cytoplasm during aspiration. The first observation points to a down-regulation of the cell's functional ability to "activate" in response to surface/chemical stimuli, and the second indicates that both the cortical and cytoskeletal networks are weakened either by disruption and/or reduction in density of the protein polymers. These observations are in line with other recently published experiments which suggest that the rheological effects of pentoxifylline on PMNs may be associated with the state of actin.

Authors
Needham, D; Armstrong, M; Hatchell, DL; Nunn, RS
MLA Citation
Needham, D, Armstrong, M, Hatchell, DL, and Nunn, RS. "Rapid deformation of "passive" polymorphonuclear leukocytes: the effects of pentoxifylline." J Cell Physiol 140.3 (September 1989): 549-557.
PMID
2777892
Source
pubmed
Published In
Journal of Cellular Physiology
Volume
140
Issue
3
Publish Date
1989
Start Page
549
End Page
557
DOI
10.1002/jcp.1041400321

Electro-mechanical permeabilization of lipid vesicles. Role of membrane tension and compressibility.

A simple micropipet technique was used to determine the critical electric field strength for membrane breakdown as a function of the applied membrane tension for three different reconstituted membranes: stearoyloleoylphosphatidylcholine (SOPC), red blood cell (RBC) lipid extract, and SOPC cholesterol (CHOL), 1:1. For these membranes the elastic area expansivity modulus increases from approximately 200 to 600 dyn/cm, and the tension at lysis increases from 5.7 to 13.2 dyn/cm, i.e., the membranes become more cohesive with increasing cholesterol content. The critical membrane voltage, Vc, required for breakdown was also found to increase with increasing cholesterol from 1.1 to 1.8 V at zero membrane tension. We have modeled the behavior in terms of the bilayer expansivity. Membrane area can be increased by either tensile or electrocompressive stresses. Both can store elastic energy in the membrane and eventually cause breakdown at a critical area dilation or critical energy. The model predicts a relation between tension and voltage at breakdown and this relation is verified experimentally for the three reconstituted membrane systems studied here.

Authors
Needham, D; Hochmuth, RM
MLA Citation
Needham, D, and Hochmuth, RM. "Electro-mechanical permeabilization of lipid vesicles. Role of membrane tension and compressibility." Biophys J 55.5 (May 1989): 1001-1009.
PMID
2720075
Source
pubmed
Published In
Biophysical Journal
Volume
55
Issue
5
Publish Date
1989
Start Page
1001
End Page
1009
DOI
10.1016/S0006-3495(89)82898-X

Thermomechanical and transition properties of dimyristoylphosphatidylcholine/cholesterol bilayers.

Mixtures of dimyristoylphosphatidylcholine (DMPC) and cholesterol (Chol) have been used to examine the effects of cholesterol on the chain crystallization transitions and thermomechanical properties in phospholipid bilayer membranes. The mechanical properties--elastic moduli and level of tension at membrane rupture--were derived from micropipet pressurization of giant single-walled vesicles. Also, the micropipet method allowed temperature-dependent area transitions to be measured at constant membrane tension. X-ray diffraction measurements were made on selected lipid/cholesterol mixtures. Wide-angle patterns and electron density profiles were used to measure bilayer thickness as an indication of chain tilt and fluidity. Vesicle area versus temperature plots showed that the main acyl chain crystallization transition of DMPC broadened and shifted to higher temperatures. Both above and below the broad transition, the elastic area compressibility modulus, K, was greatly increased with cholesterol addition. The value for the 1:1 DMPC/Chol complex was found to be approximately 700 dyn/cm, comparable to that for DMPC in the L beta' phase. However, for all concentrations above 12.5 mol % (which was weakly solid), vesicle bilayers behaved as surface liquids with no surface shear rigidity even at temperatures well below the DMPC phase transition. Area changes over the broadened transitions were reduced by cholesterol and disappeared with the addition of 50 mol % to leave the thermal area expansivity at 1.3 X 10(-3)/degrees C. These area changes are consistent with separate formation of a 1:1 DMPC/Chol complex that does not condense plus residual free lipid and lipid loosely associated with the 1:1 complex that freezes normally.(ABSTRACT TRUNCATED AT 250 WORDS)

Authors
Needham, D; McIntosh, TJ; Evans, E
MLA Citation
Needham, D, McIntosh, TJ, and Evans, E. "Thermomechanical and transition properties of dimyristoylphosphatidylcholine/cholesterol bilayers." Biochemistry 27.13 (June 28, 1988): 4668-4673.
PMID
3167010
Source
pubmed
Published In
Biochemistry
Volume
27
Issue
13
Publish Date
1988
Start Page
4668
End Page
4673

ATTRACTION BETWEEN LIPID BILAYER MEMBRANES IN CONCENTRATED SOLUTIONS OF NONADSORBING POLYMERS: COMPARISON OF MEAN-FIELD THEORY WITH MEASUREMENTS OF ADHESION ENERGY.

The authors report direct measurements of the free energy potential for adhesion of synthetic lipid bilayers in aqueous solutions of dextran (polyglucose) over a wide range of volume fraction (0. 01-0. 1) and molecular weight. These polymer solutions are well-modeled by a Flory interaction parameter of 0. 43, characteristic of a 'good' solvent. Controlled assembly of two giant bilayer vesicles was used to evaluate the free energy potential for formation of adhesive contact. The adhesion energy for neutral (phosphatidylcholine) bilayers in 0. 1 M NaCl was found to steadily increase with polymer volume fraction - without any indication of a plateau - and with little dependence of polymer size.

Authors
Evans, E; Needham, D
MLA Citation
Evans, E, and Needham, D. "ATTRACTION BETWEEN LIPID BILAYER MEMBRANES IN CONCENTRATED SOLUTIONS OF NONADSORBING POLYMERS: COMPARISON OF MEAN-FIELD THEORY WITH MEASUREMENTS OF ADHESION ENERGY." Macromolecules 21.6 (1988): 1822-1831.
Source
scival
Published In
Macromolecules
Volume
21
Issue
6
Publish Date
1988
Start Page
1822
End Page
1831

Structure and mechanical properties of giant lipid (DMPC) vesicle bilayers from 20 °C below to 10 °C above the liquid crystal-crystalline phase transition at 24 °C

We have used micromechanical tests to measure the thermoelastic properties of the liquid and gel phases of dimyristoylphosphatidylcholine (DMPC). We have found that the rippled Pβ′ phase is only formed when a vesicle is cooled to temperatures below the main acyl chain crystallization transition, Tc, under zero or very low membrane tension. We also found that the Pβ′ surface ripple or superlattice can be pulled flat under high membrane tension into a planar structure. For a ripple structure formed by acyl chains perpendicular to the projected plane, the projected area change that results from a flattening process is a direct measure of the molecular crystal angle. As such, the crystal angle was found to increase from about 24° just below Tc to about 33° below the pretransition. It was also observed that the Pβ′ superlattice did not form when annealed Lβ′ phase vesicles were heated from 5°C to Tc; likewise, ripples did not form when the membrane was held under large tension during freezing from the Lα phase. Each of these three procedures could be used to create a metastable planar structure which we have termed L*β′ since it is lamellar and plane-crystalline with acyl chains tilted to the bilayer plane. However, we show that this structure is not as condensed as the Lβ′ phase below 10°C. On the basis of observed changes in vesicle projected area at the main transition and comparison of the elastic area compressibility moduli measured for each of the structures (Lα, L*β′, and Lβ′), the Pβ′ phase is shown to be a soft crystalline solid that possesses some degree of chain disorder and slight liquidlike character. Below the pretransition temperature, bilayers exhibited a much lower compressibility indicative of further condensation to a more solid crystalline phase. At intermediate temperatures for the Pβ′ phase, we observed that the rippled surface behaved in a weakly elastic manner at low membrane tensions. On the basis of this observation, we have developed a mechanical model for the rippled phase that represents the material as a pleated surface where extensional deformations of the projected plane are derived from bending deformations of the surface facets (analogous to a "corrugated spring"). This model predicts that the ripple surface elastic modulus is proportional to the bilayer bending or curvature elastic modulus and inversely proportional to the square of the ripple amplitude. The model correlates very well with the observed mechanical behavior of the Pβ′ phase surface and yields a value for the bilayer bending modulus of 3 × 10-12 erg. © 1988 American Chemical Society.

Authors
Needham, D; Evans, E
MLA Citation
Needham, D, and Evans, E. "Structure and mechanical properties of giant lipid (DMPC) vesicle bilayers from 20 °C below to 10 °C above the liquid crystal-crystalline phase transition at 24 °C." Biochemistry 27.21 (1988): 8261-8269.
PMID
3233209
Source
scival
Published In
Biochemistry
Volume
27
Issue
21
Publish Date
1988
Start Page
8261
End Page
8269

Physical properties of surfactant bilayer membranes: Thermal transitions, elasticity, rigidity, cohesion, and colloidal interactions

Simple micromechanical methods provide direct measurements of surface cohesion, elasticity, rigidity, and mutual attraction properties of surfactant double-layer membranes in aqueous media. Temperature-dependent tests yield explicit data for thermal phase transitions. Properties of mixtures of phospholipids (neutral and charged), cholesterol, and polypeptides have been studied. The results are essential for evaluation of theories of surfactant mixing, lamellar phase transitions, colloidal stabilization, and flocculation. © 1987 American Chemical Society.

Authors
Evans, E; Needham, D
MLA Citation
Evans, E, and Needham, D. "Physical properties of surfactant bilayer membranes: Thermal transitions, elasticity, rigidity, cohesion, and colloidal interactions." Journal of Physical Chemistry 91.16 (1987): 4219-4228.
Source
scival
Published In
Journal of Physical Chemistry
Volume
91
Issue
16
Publish Date
1987
Start Page
4219
End Page
4228

Giant vesicle bilayers composed of mixtures of lipids, cholesterol and polypeptides: Thermomechanical and (mutual) adherence properties

Micromechanical tests of giant vesicle bilayer elasticity and bilayer-bilayer adhesivity have been carried out on vesicles made from mixtures of lipids, cholesterol and polypeptides. Mixtures of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) exhibited ideal solution behaviour over a temperature range that covered both liquid-to-gel phase transitions. Addition of cholesterol (CHOL) to a saturated chain lecithin (DMPC) reduced, broadened and shifted to higher temperature the main crystalline-to-liquid acyl chain transition. Cholesterol greatly reduced the membrane area compressibility and increased membrane cohesion to levels exhibited by frozen acyl chain bilayers, but maintained the bilayer in a liquid state. Addition of amphiphilic polypeptides to PC and PC-CHOL mixtures slightly increased bilayer compressibility at high temperatures; when the temperature was lowered, bilayer compressibility for DMPC-CHOL-peptide mixtures was greatly reduced to below that of the single component lipid. Cholesterol appeared to change from an association with the lipid at low temperatures to an association with the protein at high temperatures. Membrane cohesion correlated with a simple fracture energy model where the level of tension required to lyse vesicles is proportional to the square root of the elastic area compressibility modulus. Free-energy potentials for adhesion of mixed lipid (PC and PE) bilayers showed a dramatic increase as the mole fraction of PE approached unity. Based on published values of separation distance between lamellae at full hydration for each pure component, the free energy potentials for adhesion of mixed-lipid bilayers were calculated from theoretical models of the van der Waals attraction and hydration repulsion then compared with the measured values of adhesion energy. The correlation provides strong evidence that the hydration repulsion can be represented by a surface-potential theory.

Authors
Evans, E; Needham, D
MLA Citation
Evans, E, and Needham, D. "Giant vesicle bilayers composed of mixtures of lipids, cholesterol and polypeptides: Thermomechanical and (mutual) adherence properties." Faraday Discussions of the Chemical Society 81 (1986): 267-280.
PMID
3582617
Source
scival
Published In
Faraday Discussions of the Chemical Society
Volume
81
Publish Date
1986
Start Page
267
End Page
280
DOI
10.1039/DC9868100267

Inactivation of the sodium current in squid giant axons by hydrocarbons

The voltage dependence of the steady state inactivation parameter (h(∞)) of the sodium current in the squid giant axon is known to be shifted in the hyperpolarizing direction by hydrocarbons and it has been suggested that the shifts arise from thickness changes in the axon membrane, analogous to those produced in lipid bilayers (Haydon, D.A., and J.E. Kimura, 1981, J. Physiol [Lond.], 312:57-70; Haydon, D.A., and B.W. Urban, 1983, J. Physiol. [Lond.], 338-435-450; Haydon, D.A., J.R. Elliott, and B.M. Hendry, 1984, Curr. Top. Membr. Transp., 22:445-482). This hypothesis has been tested systematically by examining the effects of a range of concentrations of cyclopentane on the high-frequency capacitance per unit area both of the axonal membrane and of lipid bilayers formed for monoolein plus squalene. A similar composition has been made for cyclopropane and n-butane, both at a pressure of 1 atm. The results are consistent with the notion that thickness increases in the axolemma produce the shifts in h(∞). Except at very high concentrations, however, the thickness changes in the lipid bilayer were too small to account for the h(∞J) shifts. A possible explanation of this finding is discussed.

Authors
Elliott, JR; Haydon, DA; Hendry, BM; Needham, D
MLA Citation
Elliott, JR, Haydon, DA, Hendry, BM, and Needham, D. "Inactivation of the sodium current in squid giant axons by hydrocarbons." Biophysical Journal 48.4 (1985): 617-622.
PMID
2413918
Source
scival
Published In
Biophysical Journal
Volume
48
Issue
4
Publish Date
1985
Start Page
617
End Page
622

A quantitative explanation of the effects of some alcohols on gramicidin single-channel lifetime

The effects of n-decanol, n-hexadecanol, n-octyl(oxyethylene) 3 alcohol and cholesterol on gramicidin single-channel lifetime in planar lipid bilayers have been determined. The bilayers used were formed from a solution of monoolein in squalene. Measurements have also been made of the above compounds' effects on membrane thickness (as measured by electrical capacity and optical reflectance technique) and surface tension (as derived from bulk interfacial tension and bilayer-lens contact angle measurements). The reduction in single-channel lifetime caused by the n-alkanols may be accounted for quantitatively in terms of the effects of these compounds on bilayer thickness and surface tension. The n-octyl(oxyethylene) 3 alcohol caused an increase in single-channel lifetime which is also consistent with the thickness/tension theory. The reduction in channel lifetime caused by cholesterol, however, was much larger than would be predicted from its effects on bilayer thickness and surface tension. © 1985.

Authors
Elliott, JR; Needham, D; Dilger, JP; Brandt, O; Haydon, DA
MLA Citation
Elliott, JR, Needham, D, Dilger, JP, Brandt, O, and Haydon, DA. "A quantitative explanation of the effects of some alcohols on gramicidin single-channel lifetime." BBA - Biomembranes 814.2 (1985): 401-404.
PMID
2579676
Source
scival
Published In
BBA - Biomembranes
Volume
814
Issue
2
Publish Date
1985
Start Page
401
End Page
404

HYDRIDIZATION AND CATALYSIS BY LANTHANIDE FILMS.

Hydrogen absorption to give the dihydrides MH//2// plus //i containing interstitial hydrogen H//i has been studied for the metals Gd, Dy, Er, Yb and Lu in the form of films deposited in ultra-high vacuum on glass. Film areas were determined by Kr adsorption, and hydrogen content, in particular interstitial hydrogen H//i, characterized by gas uptake, temperature programmed desorption, electrical conductivity and work function measurements by the diode method.

Authors
Eley, DD; Needham, D
MLA Citation
Eley, DD, and Needham, D. "HYDRIDIZATION AND CATALYSIS BY LANTHANIDE FILMS." Proceedings of The Royal Society of London, Series A: Mathematical and Physical Sciences 393.1805 (1984): 257-276. (Academic Article)
Source
manual
Published In
Proceedings of The Royal Society of London, Series A: Mathematical and Physical Sciences
Volume
393
Issue
1805
Publish Date
1984
Start Page
257
End Page
276

Tensions and free energies of formation of 'solventless' lipid bilayers. Measurement of high contact angles

A method is described for the accurate measurement of the interfacial tension of lipid bilayer membranes containing little or no solvent. The tensions were obtained from the interfacial tensions of the equilibrium film-forming solution in the Plateau-Gibbs border, measured by conventional techniques, and the contact angle between the border and the bilayer. The contact angles in these systems are large (> 10°) and were estimated by a new method that involved the injection of small known volumes of lipid solution into the bilayer so as to form a lens. Results have been obtained for monoolein-triolein, monoolein-squalene, and monoolein-squalene-decane systems. Half bilayer tensions in these systems were up to ~ 1 mN m-1 less than the single interface tensions. Although bilayer tension tended to increase with bilayer thickness, the interdependence of these quantities varied with the alkane solvents present. In the monoolein-squalene-decane systems, small concentrations of decane have a larger effect on tension than on thickness. Free energies of formation of the near-solventless bilayers were much greater than estimated from the simple application of Lifshitz theory.

Authors
Needham, D; Haydon, DA
MLA Citation
Needham, D, and Haydon, DA. "Tensions and free energies of formation of 'solventless' lipid bilayers. Measurement of high contact angles." Biophysical Journal 41.3 (1983): 251-257.
PMID
6838967
Source
scival
Published In
Biophysical Journal
Volume
41
Issue
3
Publish Date
1983
Start Page
251
End Page
257

The effects of bilayer thickness and tension on gramicidin single-channel lifetime

Measurements have been made of gramicidin single-channel lifetimes in monoacylglycerol bilayers chosen so that their thickness ranged from above to below the length of the gramicidin channel. Contact angles, electrical capacities and bulk-phase interfacial tensions have also been determined for these systems. The mean channel lifetime decreased with the hydrocarbon thickness of the membrane until the latter reached 2.2 nm, after which the lifetime was relatively constant. A theoretical model has been proposed which relates the mean channel lifetime (or dissociation constant) to both the thickness and the tension of the bilayers. The analysis of the present results and of those of previous studies has led to the idea that aggregates of water molecules may play an important rǒle in the dissociation of the gramicidin channel. © 1983.

Authors
Elliott, JR; Needham, D; Dilger, JP; Haydon, DA
MLA Citation
Elliott, JR, Needham, D, Dilger, JP, and Haydon, DA. "The effects of bilayer thickness and tension on gramicidin single-channel lifetime." BBA - Biomembranes 735.1 (1983): 95-103.
PMID
6194820
Source
scival
Published In
BBA - Biomembranes
Volume
735
Issue
1
Publish Date
1983
Start Page
95
End Page
103
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