Active Solids: Topological Defect Self-Propulsion Without Flow

TL;DR

This paper introduces a minimal model for defect self-propulsion in active nematic solids, revealing a new mechanism where defects move through local nematic texture remodeling rather than fluid flow, with implications for biological tissue organization.

Contribution

It proposes a novel elastic solid-based model for defect self-propulsion, distinct from fluid-based mechanisms, explaining defect dynamics in solid-like tissues.

Findings

Defects can self-propel via local nematic texture remodeling.

The model predicts unbinding of defect pairs and stabilization of +1 defects.

Implications for tissue morphogenesis and biological organization.

Abstract

The self-propulsion of +1/2 topological defects is a hallmark of active nematic fluids, where the defects are advected by the flow field they themselves generate. In this paper we propose a minimal model for defect self-propulsion in a nematic active solid: a linear elastic medium with an embedded nematic texture that generates active stress and associated elastic strains. We show that such coupling gives rise to self-propelled +1/2 defects that move relative to the elastic medium by local remodeling of the nematic texture without advection. This mechanism is fundamentally different from the fluid case and can lead to unbinding of defect pairs and stabilization of +1 defects. Our findings might help explain how orientational order, of, for example, muscle fibers, is reconfigured during morphogenesis in solid-like tissues. The proposed mechanism may, for instance, control motility and merging of +1/2 defects, which play a crucial role in setting up the body axis during Hydra regeneration.