Fluctuation-induced dynamics of nematic topological defects

TL;DR

This study demonstrates through simulations that mesoscopic fluctuations in nematic systems can induce flow and stress patterns around topological defects similar to those in active matter, without requiring active stresses.

Contribution

It reveals that passive elastic stresses and flow-aligning behavior can produce active-like defect dynamics solely from fluctuations in nematic systems.

Findings

Fluctuations can induce flow patterns resembling active systems.

Positive half-integer defects can exhibit extensile- and contractile-like motion.

Stress fields around defects match experimental observations in epithelia.

Abstract

Topological defects are increasingly being identified in various biological systems, where their characteristic flow fields and stress patterns are associated with continuous active stress generation by biological entities. Here, using numerical simulations of continuum fluctuating nematohydrodynamics we show that even in the absence of any specific form of active stresses associated with self-propulsion, mesoscopic fluctuations in either orientational alignment or hydrodynamics can independently result in flow patterns around topological defects that resemble the ones observed in active systems. Our simulations further show the possibility of extensile- and contractile-like motion of fluctuation-induced positive half-integer topological defects. Remarkably, isotropic stress fields also reproduce the experimentally measured stress patterns around topological defects in epithelia. Our findings further reveal that extensile- or contractile-like flow and stress patterns around fluctuation-induced defects are governed by passive elastic stresses and flow-aligning behavior of the nematics.