Front speed and pattern selection of a propagating chemical front in an active fluid

TL;DR

This paper investigates how active mechanical stresses influence the speed and pattern formation of chemical fronts in reaction-diffusion systems, revealing that extensile stress accelerates fronts while contractile stress causes instabilities.

Contribution

It introduces a minimal model coupling reaction-diffusion with active mechanics, analyzing the effects of stress types on front propagation and pattern formation.

Findings

Extensile stress increases front speed beyond a critical level.

Contractile stress does not affect front speed but induces periodic instabilities.

The model extends classical reaction-diffusion theory to active, mechano-chemical systems.

Abstract

Spontaneous pattern formation in living systems is driven by reaction-diffusion chemistry and active mechanics. The feedback between chemical and mechanical forces is often essential to robust pattern formation, yet it remains poorly understood in general. In this analytical and numerical paper, we study an experimentally-motivated minimal model of coupling between reaction-diffusion and active matter: a propagating front of an autocatalytic and stress-generating species. In the absence of activity, the front is described by the the well-studied KPP equation. We find that front propagation is maintained even in active systems, with crucial differences: an extensile stress increases the front speed beyond a critical magnitude of the stress, while a contractile stress has no effect on the front speed but can generate a periodic instability in the high-concentration region behind the front. We expect our results to be useful in interpreting pattern formation in active systems with mechano-chemical coupling in vivo and in vitro.