Elasticity and mechanical instability of charged lipid bilayers in ionic solutions

TL;DR

This study uses coarse-grained Monte Carlo simulations to explore how charged lipid bilayers behave elastically in ionic solutions, revealing opposite trends in membrane rigidity depending on counterion valency and mechanisms of instability.

Contribution

It demonstrates how counterion valency influences membrane elasticity and instability mechanisms through detailed simulation analysis.

Findings

Monovalent counterions increase membrane rigidity with charge density.

Pentavalent counterions decrease membrane rigidity with charge density.

Different instability mechanisms: pore formation vs. bending instability.

Abstract

We use coarse-grained Monte Carlo simulations to study the elastic properties of charged membranes in solutions of monovalent and pentavalent counterions. The simulation results of the two cases reveal trends opposite to each other. The bending rigidity and projected area increase with the membrane charge density for monovalent counterions, while they decrease for the pentavalent ions. These observations can be related to the counterion screening of the lipid charges. While the monovalent counterions only weakly screen the Coulomb interactions, which implies a repulsive Coulomb system, the multivalent counterions condense on the membrane and, through spatial charge correlations, make the effective interactions due the charged lipids attractive. The differences in the elastic properties of the charged membranes in monovalent and multivalent counterion solutions are reflected in the mechanisms leading to their mechanical instability at high charge densities. In the former case, the membranes develop pores to relieve the electrostatic tensile stresses, while in the latter case, the membrane exhibit large wavelength bending instability.