Thin film models for active gels

TL;DR

This paper develops a thin film model for active liquid crystals, incorporating active stresses and defect dynamics, providing new insights into the behavior of active gels in confined geometries.

Contribution

It introduces a novel thin film model based on the Beris-Edwards theory that captures defect dynamics and active stress effects in active gels.

Findings

Model captures defect dynamics in bulk and wall regions.

Analytic expressions relate anchoring, thickness, and activity to flow transitions.

Extends previous models by including active contributions and defect structures.

Abstract

In this study we present a free-boundary problem for an active liquid crystal based on the Beris-Edwards theory that uses a tensorial order parameter and includes active contributions to the stress tensor to analyse the rich defect structure observed in applications such as the Adenosinetriphosphate (ATP) driven motion of a thin film of an actin filament network. The small aspect ratio of the film geometry allows for an asymptotic approximation of the free-boundary problem in the limit of weak elasticity of the network and strong active terms. The new thin film model captures the defect dynamcs in the bulk as well as wall defects and thus presents a significant extension of previous models based on the Lesli-Erickson-Parodi theory. Analytic expression are derived that reveal the interplay of anchoring conditions, film thickness and active terms and their control of transitions of flow structure.