Generic instabilities in a fluid membrane coupled to a thin layer of ordered active polar fluid

TL;DR

This paper presents a theoretical analysis of a coupled membrane-active fluid system, revealing generic instabilities caused by activity and potential propagating waves, with implications for understanding active biological membranes.

Contribution

It introduces a coarse-grained two-dimensional model for a membrane coupled to an active polar fluid layer, highlighting activity-induced instabilities and wave phenomena.

Findings

System is generically linearly unstable due to activity.

Under certain conditions, underdamped propagating waves can occur.

Results have phenomenological relevance for active membrane systems.

Abstract

We develop an effective two-dimensional coarse-grained description for the coupled system of a planar fluid membrane anchored to a thin layer of polar ordered active fluid below. The macroscopic orientation of the active fluid layer is assumed to be perpendicular to the attached membrane. We demonstrate that {\em activity} or nonequilibrium drive of the active fluid makes such a system generically linearly unstable for either signature of a model parameter $\Delta\mu$ that characterises the strength of activity. Depending upon boundary conditions and within a range of the model parameters, underdamped propagating waves may be present in our model. We discuss the phenomenological significance of our results.