Electrostatic Repulsion of Positively Charged Vesicles and Negatively Charged Objects

A positively charged, mixed bilayer vesicle in the presence of negatively charged surfaces (for example, colloidal particles) can spontaneously partition into an adhesion zone of definite area, and another zone that repels additional negative objects. Although the membrane itself has nonnegative charge in the repulsive zone, negative counterions on the interior of the vesicle spontaneously aggregate there, and present a net negative charge to the exterior. Beyond the fundamental result that oppositely charged objects can repel, our mechanism helps explain recent experiments on surfactant vesicles.Comment: Latex using epsfig and afterpage; pdf available at http://www.physics.upenn.edu/~nelson/Mss/repel.pd

Pharmacokinetic and behavioral characterization of a longterm antipsychotic delivery system in rodents and rabbits

Rationale: Non-adherence with medication remains the major correctable cause of poor outcome in schizophrenia. However, few treatments have addressed this major determinant of outcome with novel long-term delivery systems. Objectives: The aim of this study was to provide biological proof of concept for a long-term implantable antipsychotic delivery system in rodents and rabbits. Materials and methods: Implantable formulations of haloperidol were created using biodegradable polymers. Implants were characterized for in vitro release and in vivo behavior using prepulse inhibition of startle in rats and mice, as well as pharmacokinetics in rabbits. Results: Behavioral measures demonstrate the effectiveness of haloperidol implants delivering 1 mg/kg in mice and 0.6 mg/kg in rats to block amphetamine (10 mg/kg) in mice or apomorphine (0.5 mg/kg) in rats. Additionally, we demonstrate the pattern of release from single polymer implants for 1 year in rabbits. Conclusions: The current study suggests that implantable formulations are a viable approach to providing long-term delivery of antipsychotic medications in vivo using animal models of behavior and pharmacokinetics. In contrast to depot formulations, implantable formulations could last 6 months or longer. Additionally, implants can be removed throughout the delivery interval, offering a degree of reversibility not available with depot formulations

Membrane-induced interactions between curvature-generating protein domains: the role of area perturbation

Membrane deformation by asymmetric crescent-shaped proteins such as BAR-domains is calculated, using a mean field model that accounts for both bending and area stretch deformations. The penalties associated with membrane bending and area perturbation lead to moderately long-ranged (order 10 nm), non-monotonic, membrane-induced interactions between proteins that may prevent the formation of closely packed aggregates. As a result, BAR-domain proteins may favor the formation of an ordered array with a specific separation between domains whose spacing is set by the ratio between the bending and area stretch moduli

Bilayer degradation in reactive environments

Lipid vesicles, or liposomes have been widely studied both as a model for cell membranes and for applications such as drug delivery. As a rule, their aqueous environment (in vitro or in vivo) contains various degradation agents, ranging from free radicals to acids and enzymes. This paper investigates the degradation of lipid vesicles as a function of environmental conditions using 3d Monte-Carlo simulations. The time-scale for bilayer degradation is found to be independent of the liposome size, but highly sensitive to the concentration of degradation molecules in solution and to the rate of the degradation reaction

Lipid-Nucleic Acid Supramolecular Complexes: Lipoplex Structure and the Kinetics of Formation

The need for synthetic gene therapy or gene silencing vehicles that can insert therapeutic nucleic acids (DNA or siRNA) into cells (so-called transfection) has focused interest on lipid-nucleic acid assemblies (lipoplexes). This paper reviews the kinetics pathways leading to lipoplex formation and structure. The process is qualitatively comparable to those of cluster nucleation and growth and to the adsorption of polyelectrolytes on colloidal particles: Initially is a rapid stage where the nucleic acid binds onto the surface of the cationic lipid aggregate (adsorption, or nucleation). This is followed by an intermediate step where the lipid/nucleic acid complexes flocculate to form larger structures (growth). The last and final step involves internal rearrangement, where the overall global structure remains constant while local adjustment of the nucleic acid/lipid organization takes place until the equilibrium lipoplex characteristics are obtained. This step can require unusually long time scales of order hours or longer. Understanding the kinetics of lipoplex formation is not only of fundamental interest as a multi-component, multi-length scale and multi-time scale process, but also has significant implications for the utilization of lipoplexes as carriers for gene delivery and gene silencing agents

The Effect of Chain Length on Protein Solubilization in Polymer-Based Vesicles (Polymersomes)

Using a mean-field analysis we derive a consistent model for the perturbation of a symmetric polymeric bilayer due to the incorporation of transmembrane proteins, as a function of the polymer molecular weight and the protein dimensions. We find that the mechanism for the inhibition of protein incorporation in polymeric bilayers differs from that of their inclusion in polymer-carrying lipid vesicles; in polymersomes, the equilibrium concentration of transmembrane proteins decreases as a function of the thickness mismatch between the protein and the bilayer core, whereas in liposomes the presence of polymer chains affects the protein adsorption kinetics. Despite the increased stiffness of polymer bilayers (when compared to lipid ones), their perturbation decay length and range of protein-protein interaction is found to be relatively long. The energetic penalty due to protein adsorption increases relatively slowly as a function of the polymer chain length due to the self-assembled nature of the polymer bilayer. As a result, we predict that transmembrane proteins may be incorporated in significant numbers even in bilayers where the thickness mismatch is large