Molecular motors stiffen non-affine semiflexible polymer networks

TL;DR

This study demonstrates how molecular motors induce stiffening in semiflexible polymer networks by pulling out bending modes, leading to nonlinear elastic responses relevant for cellular mechanics and biomimetic material design.

Contribution

The paper introduces a simulation model showing how motor-generated forces cause stiffening in filament networks by suppressing bending modes, a novel insight into active network mechanics.

Findings

Motor stresses cause network stiffening by suppressing bending modes.

Heterogeneous motor activity induces a transition to a stretching-dominated regime.

Results suggest mechanisms for tunable mechanics in cellular and biomimetic systems.

Abstract

Reconstituted filamentous actin networks with myosin motor proteins form active gels, in which motor proteins generate forces that drive the network far from equilibrium. This motor activity can also strongly affect the network elasticity; experiments have shown a dramatic stiffening in in vitro networks with molecular motors. Here we study the effects of motor generated forces on the mechanics of simulated 2D networks of athermal stiff filaments. We show how heterogeneous internal motor stresses can lead to stiffening in networks that are governed by filament bending modes. The motors are modeled as force dipoles that cause muscle like contractions. These contractions "pull out" the floppy bending modes in the system, which induces a cross-over to a stiffer stretching dominated regime. Through this mechanism, motors can lead to a nonlinear network response, even when the constituent filaments are themselves purely linear. These results have implications for the mechanics of living cells and suggest new design principles for active biomemetic materials with tunable mechanical properties.