Statistical mechanics and dynamics of two supported stacked lipid bilayers

TL;DR

This paper presents a theoretical study of the physics and dynamics of double supported lipid bilayers, emphasizing fluctuation effects, stability conditions, and hydrodynamic interactions, to better understand biomembrane models.

Contribution

It introduces a Gaussian variational approach to analyze membrane fluctuations and stability, highlighting the dependence on temperature and elastic properties, which is a novel theoretical insight.

Findings

Membrane fluctuation effects depend strongly on temperature and elastic moduli.

Conditions for a nearly free upper membrane while remaining surface-bound are identified.

Hydrodynamic interactions influence damping rates of membrane modes.

Abstract

The statistical physics and dynamics of double supported bilayers are studied theoretically. The main goal in designing double supported lipid bilayers is to obtain model systems of biomembranes: the upper bilayer is meant to be almost freely floating, the substrate being screened by the lower bilayer. The fluctuation-induced repulsion between membranes and between the lower membrane and the wall are explicitly taken into account using a Gaussian variational approach. It is shown that the variational parameters, the "effective" adsorption strength and the average distance to the substrate, depend strongly on temperature and membrane elastic moduli, the bending rigidity and the microscopic surface tension, which is a signature of the crucial role played by membrane fluctuations. The range of stability of these supported membranes is studied, showing a complex dependence on bare adsorption strengths. In particular, the experimental conditions to have an upper membrane slightly perturbed by the lower one and still bound to the surface are found. Included in the theoretical calculation of the damping rates associated with membrane normal modes are hydrodynamic friction by the wall and hydrodynamic interactions between both membranes.