Oscillatory collective motion in viscoelastic and elastic active fluids and solids under circular confinement

TL;DR

This paper demonstrates that oscillatory and translational collective motions observed in confined active biofilms are generic phenomena that occur across a broad spectrum of viscoelastic fluids and solids, not limited to elastic solids.

Contribution

It extends previous findings by showing these collective behaviors are universal in various viscoelastic active materials, not just elastic solids.

Findings

Oscillatory collective motion is common in viscoelastic active fluids.

Translational migration modes also emerge broadly in these systems.

Phenomena are not limited to elastic solids but are more general.

Abstract

In an inspiring recent study, Xu et al. [Nat. Phys. 19, 46 (2023)] observed for a living active biofilm under circular confinement two emergent dynamic modes of collective motion in the film. One corresponds to global rotational motion of oscillating sense of rotation, the other one to uniformly translating motion of rotating migration direction. The authors reproduced these features in a discretized theoretical model for elastic active solids. We here demonstrate that the discovered fundamental phenomena are generic and emerge abundantly for a broad range of viscoelastic fluids and solids. Elastic solids represent only one limiting case.