Electroporation dynamics of giant lipid vesicles

Electroporation is an efficient method for intracellular delivery. Although popular, the molecular details of this process are not well understood. Studying of various aspects of membrane electroporation using cells is difficult due to their inherent complexity. The use of membrane models such as giant unilamellar vesicles (GUVs) offers the advantage of well-controlled conditions and direct visualization with optical microscopy. Electric fields induce deformation and poration of GUVs. The electrodeformation induced depend on the conductivity ratio between the inner and outer vesicle solutions, and can be either into a prolate or an oblate shape. For strong enough pulses, visible macropores open. After the end of the pulse, the vesicle shape relaxes back to its original shape and pores usually reseal, restoring membrane integrity. The dynamics of these processes are governed by the material and mechanical properties of the lipid bilayer. Here, we study the electrodeformation/poration dynamics of GUVs of different composition and in different media. The mechanical response of GUVs to electric pulses is assessed through the vesicle relaxation time after electrodeformation, t relax, and pore closure time, T pore. From the one side, the effect of residual agarose encapsulated in GUVs grown from hybrid films of agarose and lipids is investigated. From the other side, the presence of the negatively charged phospholipid POPG in the membrane is studied in the presence/absence of salt. The presence of residual agarose in the GUVs alters the mechanical response of GUVs: Both t relax and T pore show a much broader distribution of values towards slower dynamics. In addition, unusual behavior after pulse application is often observed, including very long-lived pores, increased membrane permeability, and expulsion of a polymer network through the macropore. Pores induced in GUVs containing POPG may open indefinitely and the vesicles burst. This bursting was observed much more frequently for GUVs with higher POPG fraction and in the presence of salt. ACKNOWLEDGMENTS FAPESP

Viscosity of fluid membranes measured from vesicle deformation

Viscosity is a key mechanical property of cell membranes that controls time-dependent processes such as membrane deformation and diffusion of embedded inclusions. Despite its importance, membrane viscosity remains poorly characterized because existing methods rely on complex experimental designs and/or analyses. Here, we describe a facile method to determine the viscosity of bilayer membranes from the transient deformation of giant unilamellar vesicles induced by a uniform electric field. The method is non-invasive, easy to implement, probe-independent, high-throughput, and sensitive enough to discern membrane viscosity of different lipid types, lipid phases, and polymers in a wide range, from 10$^{-8}$ to 10$^{-4}$ Pa.s.m. It enables fast and consistent collection of data that will advance understanding of biomembrane dynamics

Nonspecific membrane-matrix interactions influence diffusivity of lipid vesicles in hydrogels

The diffusion of extracellular vesicles and liposomes in vivo is affected by different tissue environmental conditions and is of great interest in the development of liposome-based therapeutics and drug-delivery systems. Here, we use a bottom-up biomimetic approach to better isolate and study steric and electrostatic interactions and their influence on the diffusivity of synthetic large unilamellar vesicles in hydrogel environments. Single-particle tracking of these extracellular vesicle-like particles in agarose hydrogels as an extracellular matrix model shows that membrane deformability and surface charge affect the hydrogel pore spaces that vesicles have access to, which determines overall diffusivity. Moreover, we show that passivation of vesicles with PEGylated lipids, as often used in drug-delivery systems, enhances diffusivity, but that this effect cannot be fully explained with electrostatic interactions alone. Finally, we compare our experimental findings with existing computational and theoretical work in the field to help explain the nonspecific interactions between diffusing particles and gel matrix environments

Ralaxation of deformed drops, vesicles, and cells

The deformation of drops, vesicles, and cells constitutes an important class of problems in chemical and biomedical engineering and is often explored as a means to study interfacial dynamics and mechanical properties of the lipid membrane. Less attention has been paid to the relaxation process after the deforming mechanism is removed. In this study, analyses of such process are presented. A drop, vesicle, or cell of spherical shape at rest is initially deformed into a spheroid. The relaxation process is then solved within the same theoretical framework in both small- and moderate-deformation limits. Different regimes are discovered. For sufficiently small initial deformations, the change in the membrane tension is a negligible higher-order effect for both vesicles and cells, and they behave identically to drops in the relaxation process. For moderate initial deformations, vesicle and cell relaxation is dominantly governed by the folding of undulations on the lipid membrane which differs from the behavior of a drop. Membrane properties, namely, membrane tension and bending rigidity, are the key parameters governing this dynamic process. A detailed comparison with experimental data for vesicles/cells is performed, and the results are presented and discussed