Noise-induced transitions from contractile to extensile active stress in isotropic fluids

TL;DR

This paper demonstrates through analysis and simulations that in isotropic active fluids, nonlinearities and force-density coupling enable transitions between contractile and extensile stress states, explaining experimental observations in tissues.

Contribution

It reveals the conditions under which active stress transitions occur in isotropic fluids, highlighting the roles of nonlinearities and force-density coupling.

Findings

Transitions between contractile and extensile stress are possible.

Nonlinearities are essential for stress state transitions.

Force-density coupling facilitates the transition process.

Abstract

Tissues of living cells are a prime example of active fluids. There is experimental evidence that tissues generate extensile active stress even though their constituting cells are contractile. Fluctuating forces that could result from cell-substrate interactions have been proposed to be able to induce a transition from contractile to extensile active stress. Through analytic calculations and numerical computations, we show that in isotropic active fluids, nonlinearities and a coupling between fluctuating forces and fluid density are necessary for such a transition to occur. Here, both transitions from extensile to contractile and vice versa are possible.