Rapid local compression in active gels is caused by nonlinear network response

TL;DR

This study reveals that active actin gels exhibit rapid local compression due to nonlinear filament responses, driven by myosin motors, leading to large-scale stiffening and distinct fluctuation patterns.

Contribution

It demonstrates how nonlinear actin filament mechanics cause rapid local compression in active gels, advancing understanding of force propagation in cytoskeletal networks.

Findings

Rapid local compression observed in active gels

Nonlinear filament response causes large-scale stiffening

Probe fluctuations reveal anomalous compression propagation

Abstract

The actin cytoskeleton in living cells generates forces in conjunction with myosin motor proteins to directly and indirectly drive essential cellular processes. The semiflexible filaments of the cytoskeleton can respond nonlinearly to the collective action of motors. We here investigate mechanics and force generation in a model actin cytoskeleton, reconstituted in vitro, by observing the response and fluctuations of embedded micron-scale probe particles. Myosin mini-filaments can be modelled as force dipoles and give rise to deformations in the surrounding network of cross-linked actin. Anomalously correlated probe fluctuations indicate the presence of rapid local compression of the network that emerges in addition to the ordinary linear shear elastic (incompressible) response to force dipoles. The anomalous propagation of compression can be attributed to the nonlinear response of actin filaments to the microscopic forces, and is quantitatively consistent with motor-generated large-scale stiffening of the gels.