Instability and front propagation in laser-tweezed lipid bilayer tubules

TL;DR

This paper investigates the mechanisms behind the 'pearling' instability in laser-tweezed lipid tubules, emphasizing boundary conditions, steady-state lipid flow, and the effects of noise, leading to new insights into front propagation.

Contribution

It introduces a boundary condition framework based on fixed chemical potentials and explores how laser intensity profiles induce lipid flow and instability, providing new qualitative predictions.

Findings

Steady-state lipid flow driven by laser-induced surface tension gradients.

Predictions of front propagation behavior depending on tubule length.

Effects of thermal fluctuations on instability dynamics.

Abstract

We study the mechanism of the `pearling' instability seen recently in experiments on lipid tubules under a local applied laser intensity. We argue that the correct boundary conditions are fixed chemical potentials, or surface tensions \Sigma, at the laser spot and the reservoir in contact with the tubule. We support this with a microscopic picture which includes the intensity profile of the laser beam, and show how this leads to a steady-state flow of lipid along the surface and gradients in the local lipid concentration and surface tension (or chemical potential). This leads to a natural explanation for front propagation and makes several predictions based on the tubule length. While most of the qualitative conclusions of previous studies remain the same, the `ramped' control parameter (surface tension) implies several new qualitative results. We also explore some of the consequences of front propagation into a noisy (due to pre-existing thermal fluctuations) unstable medium.