Monitoring and modulating ion traffic in hybrid lipid/polymer vesicles

Abstract

Controlling the traffic of molecules and ions across membranes is a critical feature in a number of biologically relevant processes and highly desirable for the development of technologies based on membrane materials. In this paper, ion transport behavior of hybrid lipid/polymer membranes was studied in the absence and presence of ion transfer agents. A pH-sensitive fluorophore was used to investigate ion (H/OH) permeability across hybrid lipid/polymer membranes as a function of the fraction of amphiphilic block copolymer. It was observed that vesicles with intermediate lipid/polymer ratios tend to be surprisingly more permeable to ion transport than the pure lipid or pure polymer vesicles. Hybrid vesicle permeability could be further modulated with valinomycin, nigericin, or gramicidin A, which significantly expedite the dissipation of externally-imposed pH gradients by facilitating the transport of the rate-limiting co-ions (e.g. K) ions across the membrane. For gramicidin A, ion permeability decreased with increasing polymer mole fraction, and the method of introduction of gramicidin A into the membrane played an important role. Strategies to incorporate biofunctional molecules and facilitate their activity in synthetic systems are highly desirable for developing artificial organelles or other synthetic compartmentalized structures requiring control over molecular traffic across biomimetic membranes.

Hybrid Lipid-Polymer Bilayers: pH-Mediated Interactions between Hybrid Vesicles and Glass

“…The jump for pure polymer vesicles is especially striking, and film morphologies of supported polymer bilayers at low pH and adsorbed polymer vesicles at pH = 5. The thicknesses of 10 and 25 mol % polymer hybrid bilayers estimated from QCM-D data are greater than~6.5 nm membrane thicknesses measured previously by cryogenic transmission electron microscopy (cryo-TEM) [31]. This discrepancy between measurements using QCM-D and cryo-TEM is not surprising because soft materials, particularly polymers that couple strongly to water like PEO, have similar contrast to the surrounding fluid and do not show up well in cryo-TEM.…”

“…Hybrid membrane materials would enable tunable membrane permeability and diffusivity [30], and greater hydrodynamic stability (e.g., vesicles that do not aggregate over time) [26]. In addition, hybrid lipid/polymer membranes are amenable to the reconstitution of membrane proteins [31,32], and may even enhance their stability [33], including stability in solid supported membranes [23]. These properties are all, in principle, tunable by adjusting the composition of the hybrid vesicles, and may lead to more versatile platforms for robust biosensors that operate by mimicking the properties and functions of biological membranes.…”

Hybrid Vesicular Drug Delivery Systems for Cancer Therapeutics

“…An important feature of hybrid polymer–lipid vesicles is the fact that the presence of copolymer increases the stability of the membranes, which are thus more resistant to dehydration and freeze–thaw cycles . Another remarkable characteristic of such vesicles is that they are more ion permeable than liposomes or polymersomes . This enhanced permeability could be due to the size mismatch between the lipid moieties and polymeric amphiphiles or the dynamic equilibrium between the wormlike micelles and the vesicles .…”

“…Another remarkable characteristic of such vesicles is that they are more ion permeable than liposomes or polymersomes . This enhanced permeability could be due to the size mismatch between the lipid moieties and polymeric amphiphiles or the dynamic equilibrium between the wormlike micelles and the vesicles . The aforementioned properties enable hybrid vesicles to be desirable materials for the production of cell membrane mimics and biosensors rather than drug carriers.…”

Hybrid Vesicle Stability under Sterilisation and Preservation Processes Used in the Manufacture of Medicinal Formulations

“…Liposomes, composed of natural lipids, form bilayer membranes that closely mimic the structural matrix of native biomembranes. This makes them highly biocompatible and provides a native-like environment if integral membrane proteins are desired to add functionality to the membrane [23][24][25][26][27]. However, deformations, but weak under stretching deformations, with a lysis strain of less than 5% [28,29].…”