Discontinuous fluidisation transition in assemblies of actively-deforming particles: A new paradigm for collective motion in dense active materials

TL;DR

This paper introduces a new model of actively-deforming particles where volume fluctuations induce collective motion, revealing a first-order phase transition akin to active yielding in dense active materials.

Contribution

It presents the first example of an active yielding transition driven solely by volume fluctuations, contrasting with self-propulsion mechanisms.

Findings

Collective motion emerges from active volume fluctuations.

The transition is a nonequilibrium first-order phase transition.

Behavior resembles mechanical response of soft solids under deformation.

Abstract

Tracking experiments in dense biological tissues reveal a diversity of sources f or local energy injection at the cell scale. The effect of cell motility has been largely studied, but much less is known abo ut the effect of the observed volume fluctuations of individual cells. We devise a simple microscopic model of `actively-deforming' particles where local fluctuations of the particle size constitute a unique source of motion. We demonstrate that collective motion can emerge under the sole influence of such active volume fluctuations. We interpret the onset of diffusive motion as a nonequilibrium first-order phase transition, which arises at a well-defined amplitude of self-deformation. This behaviour contrasts with the glassy dynamics produced by self-propulsion, but resembles the mechanical response of soft solids under mechanical deformation. It thus constitutes the first example of active yielding transition.