Spontaneous Flows and Quantum Analogies in Heterogeneous Active Nematic Films

TL;DR

This paper explores how heterogeneity in activity affects spontaneous flows in active nematic films, revealing a connection to quantum mechanics and demonstrating significant impacts on flow properties relevant to biological systems.

Contribution

It introduces a novel analysis of heterogeneous activity in active nematics, linking flow transitions to Schrödinger's equation and showing how activity variations alter flow behavior.

Findings

Heterogeneity can modify the threshold for flow transition.

Activity steps can reverse or reduce fluid flux.

Interfaces induce shear flows affecting biological processes.

Abstract

Incorporating the inherent heterogeneity of living systems into models of active nematics is essential to provide a more realistic description of biological processes such as bacterial growth, cell dynamics and tissue development. Spontaneous flow of a confined active nematic is a fundamental feature of these systems, in which the role of heterogeneity has not yet been considered. We therefore determine the form of spontaneous flow transition for an active nematic film with heterogeneous activity, identifying a correspondence between the unstable director modes and solutions to Schr\"{o}dinger's equation. We consider both activity gradients and steps between regions of distinct activity, finding that such variations can change the signature properties of the flow. The threshold activity required for the transition can be raised or lowered, the fluid flux can be reduced or reversed and interfaces in activity induce shear flows. In a biological context fluid flux influences the spread of nutrients while shear flows affect the behaviour of rheotactic microswimmers and can cause the deformation of biofilms. All the effects we identify are found to be strongly dependent on not simply the types of activity present in the film but also on how they are distributed.