Pore-Spanning Lipid Membrane under Indentation by a Probe Tip: a Molecular Dynamics Simulation Study

TL;DR

This study uses molecular dynamics simulations to analyze how a lipid membrane spanning a nanopore responds to indentation, revealing structural transitions, rupture behavior, and the connection between microscopic and macroscopic properties.

Contribution

It provides detailed insights into the local structural changes and rupture mechanisms of lipid membranes under mechanical indentation, linking microscopic molecular behavior to macroscopic stability.

Findings

Membrane bends and fringes glide downward during indentation.

A phase transition from bilayer to interdigitated structure occurs before rupture.

Force-indentation curves reveal the membrane's mechanical response.

Abstract

We study the indentation of a free-standing lipid membrane suspended over a nanopore on a hydrophobic substrate by means of molecular dynamics simulations. We find that in the course of indentation, the membrane bends at the point of contact, and the fringes of the membrane glide downward intermittently along the pore edges and stop gliding when the fringes reach the edge bottoms. The bending continues afterwards, and the large strain eventually induces a phase transition in the membrane, transformed from a bilayered structure to an interdigitated structure. The membrane is finally ruptured when the indentation goes deep enough. Several local physical quantities in the pore regions are calculated, which include the tilt angle of lipid molecules, the nematic order, the included angle and the distance between neighboring lipids. The variations of these quantities reveal many detailed, not-yet-specified local structural transitions of lipid molecules under indentation. The force-indentation curve is also studied and discussed. The results make connection between the microscopic structure and the macroscopic properties, and provide deep insight in the understanding of the stability of a lipid membrane spanning over a nanopore.