A vesicle microrheometer for high-throughput viscosity measurements of lipid and polymer membranes

Abstract

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.

Protein-coated nanoparticles exhibit Lévy flights on a suspended lipid bilayer

“…There are considerable discrepancies between the reported membrane viscosity η m from the motion of particles strongly attached to a lipid bilayer. 46,49,50 We cannot disprove that the NPs start to cluster while moving along the bilayer surface. Thus, it is not possible to clearly identify the physical origin behind the expected theoretical diffusion constant and the measured experimental diffusion constant.…”

Kinetic relaxation of giant vesicles validates diffusional softening in a binary lipid mixture

“…Accepting the diffusional softening mechanism, cholesterol is expected to soften a DOPC bilayer, in the absence of a stiffening effect. Note however, that to fully resolve the reported discrepancy, membrane viscosity contributions in time-correlation analysis should be interrogated; recent analysis indicates that viscosity affects a broader array of undulations of smaller liposomes than previously anticipated, suggesting another possible change in the interpretation of spin echo experiments [44].…”