Stabilization of active matter by flow-vortex lattices and defect ordering

TL;DR

This paper explores how friction controls the transition between wet and dry active matter, revealing vortex lattice formation and defect ordering that could inform active material design.

Contribution

It introduces a theoretical and numerical framework showing friction as a key parameter in wet-dry active matter crossover and uncovers vortex lattice and defect ordering phenomena.

Findings

Vortex lattices form at the wet-dry crossover.

Topological defects exhibit spatial ordering.

Vortex and defect ordering resemble active crystal structures.

Abstract

Active systems, from bacterial suspensions to cellular monolayers, are continuously driven out of equilibrium by local injection of energy from their constituent elements and exhibit turbulent-like and chaotic patterns. Here we demonstrate both theoretically and through numerical simulations, that the crossover between wet active systems, whose behaviour is dominated by hydrodynamics, and dry active matter where any flow is screened, can be achieved by using friction as a control parameter. Moreover we discover unexpected vortex ordering at this wet-dry crossover. We show that the self organisation of vortices into lattices is accompanied by the spatial ordering of topological defects leading to active crystal-like structures. The emergence of vortex lattices, which leads to the positional ordering of topological defects, suggests potential applications in the design and control of active materials.