Effect of Bilayer Thickness on Membrane Bending Rigidity

Abstract

The bending rigidity k(c) of bilayer vesicles self-assembled from amphiphilic diblock copolymers has been measured using single- and dual-micropipet techniques. These copolymers are nearly a factor of 5 greater in hydrophobic membrane thickness d than their lipid counterparts and an order of magnitude larger in molecular weight M(n). The macromolecular structure of these amphiphiles lends insight into and extends relationships for traditional surfactant behavior. We find the scaling of k(c) with thickness to be nearly quadratic, in good agreement with existing theories for bilayer membranes. The results here are key to understanding and designing soft interfaces such as biomembrane mimetics.

Adhesion of Polymer Vesicles

“…The brush architecture described in the paper of Komura and Safran provides a prediction for the bending modulus of mixed polymer layers as a function of their molecular weight difference, concentration, and correlation exponent. While the area expansion, shear, and bending modulus for pure OB2 and OB18 have been reported previously [25], we report the bending modulus of mixed polymer vesicles measured with micropipette aspiration. For bending moduli below 50 kT, a single pipette technique is used to measure the tension-strain curve for unilamellar vesicles.…”

Self‐Assembled Block Copolymer Aggregates: From Micelles to Vesicles and their Biological Applications

“…The robust nature of polymeric vesicles was established in early studies, with micromanipulation verifying a ten-fold increase in critical areal strain before rupture compared to lipid vesicles. [42,49,50] Higher copolymer molecular weights led to an increase in membrane thickness, which in turn led to vesicles with greater bending rigidities, k c . [49,50] Perhaps surprisingly, the membrane elasticity (K a ) of polymeric vesicles has been proven to be relatively independent of molecular weight, with similar K a values being observed as those reported for phospholipid vesicles.…”

“…[42,49,50] Higher copolymer molecular weights led to an increase in membrane thickness, which in turn led to vesicles with greater bending rigidities, k c . [49,50] Perhaps surprisingly, the membrane elasticity (K a ) of polymeric vesicles has been proven to be relatively independent of molecular weight, with similar K a values being observed as those reported for phospholipid vesicles. This elasticity is dominated by the chemical nature of the membrane-solvent interface and hence is related to the surface tension, g. [49] Experimental studies of polymeric membrane structures have shed some light on their enhanced mechanical properties.…”

Computer simulation of aqueous block copolymer assemblies: Length scales and methods

“…Pipette aspiration results 18 showed that diblock copolymer membranes have similar area expansion moduli as lipid membranes, but their toughness (defined as the stored energy at which membrane rupture occurs) extends to $20% area strain, while lipid membranes can support strains of only $5%. A study 19 on the bending rigidity of diblock copolymer membranes reported a quadratic scaling with increasing hydrophobic thickness, with values similar to that of lipid membranes for comparable molecular weights. The shear viscosity was found to be about 500 times larger than that of lipid membranes.…”