7 research outputs found
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 to 10 Pa.s.m. It enables fast and
consistent collection of data that will advance understanding of biomembrane
dynamics
Fluctuation spectroscopy of giant unilamellar vesicles using confocal and phase contrast microscopy
A widely used method to measure the bending rigidity of bilayer membranes is
fluctuation spectroscopy, which analyses the thermally-driven membrane
undulations of giant unilamellar vesicles recorded with either phase-contrast
or confocal microscopy. Here, we analyze the fluctuations of the same vesicle
using both techniques and obtain consistent values for the bending modulus. We
discuss the factors that may lead to discrepancies
Assessing membrane material properties from the response of giant unilamellar vesicles to electric fields
Knowledge of the material properties of membranes is crucial to understanding cell viability and physiology. A number of methods have been developed to probe membranes in vitro, utilizing the response of minimal biomimetic membrane models to an external perturbation. In this review, we focus on techniques employing giant unilamellar vesicles (GUVs), model membrane systems, often referred to as minimal artificial cells because of the potential they offer to mimick certain cellular features. When exposed to electric fields, GUV deformation, dynamic response and poration can be used to deduce properties such as bending rigidity, pore edge tension, membrane capacitance, surface shear viscosity, excess area and membrane stability. We present a succinct overview of these techniques, which require only simple instrumentation, available in many labs, as well as reasonably facile experimental implementation and analysis.
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Torsional fracture of viscoelastic liquid bridges
Short liquid bridges are stable under the action of surface tension. In applications like electronic packaging, food engineering, and additive manufacturing, this poses challenges to the clean and fast dispensing of viscoelastic fluids. Here, we investigate how viscoelastic liquid bridges can be destabilized by torsion. By combining high-speed imaging and numerical simulation, we show that concave surfaces of liquid bridges can localize shear, in turn localizing normal stresses and making the surface more concave. Such positive feedback creates an indent, which propagates toward the center and leads to breakup of the liquid bridge. The indent formation mechanism closely resembles edge fracture, an often undesired viscoelastic flow instability characterized by the sudden indentation of the fluid\u27s free surface when the fluid is subjected to shear. By applying torsion, even short, capillary stable liquid bridges can be broken in the order of 1 s. This may lead to the development of dispensing protocols that reduce substrate contamination by the satellite droplets and long capillary tails formed by capillary retraction, which is the current mainstream industrial method for destabilizing viscoelastic liquid bridges