Instabilities and Oscillations in Isotropic Active Gels

TL;DR

This paper develops a continuum model for isotropic active gels, revealing how active crosslinkers induce instabilities and oscillations, unifying microscopic muscle models with large-scale active solid behavior.

Contribution

It introduces a generic continuum elasticity framework for isotropic active gels, incorporating active crosslinker dynamics and explaining oscillations and instabilities.

Findings

Large activity causes contractile instability.

Smaller activity levels induce spontaneous oscillations.

The model unifies microscopic and macroscopic descriptions of active solids.

Abstract

We present a generic formulation of the continuum elasticity of an isotropic crosslinked active gel. The gel is described by a two-component model consisting of an elastic network coupled frictionally to a permeating fluid. Activity is induced by active crosslinkers that undergo an ATP-activated cycle and transmit forces to the network. The on/off dynamics of the active crosslinkers is described via rate equations for unbound and bound motors. For large activity motors yield a contractile instability of the network. At smaller values of activity, the on/off motor dynamics provides an effective inertial drag on the network that opposes elastic restoring forces, resulting in spontaneous oscillations. Our work provides a continuum formulation that unifies earlier microscopic models of oscillations in muscle sarcomeres and a generic framework for the description of the large scale properties of isotropic active solids.