Fiber networks amplify active stress

TL;DR

This paper presents a theoretical study showing how fiber networks amplify active stresses generated by molecular motors, with implications for understanding force transmission in biological tissues.

Contribution

It introduces a model explaining how local active forces are amplified and rectified in disordered fiber networks, highlighting the role of buckling and network microstructure.

Findings

Active forces are rectified towards isotropic contraction.

Fiber buckling amplifies stress near active units.

Stress amplification saturates at high active unit densities.

Abstract

Large-scale force generation is essential for biological functions such as cell motility, embryonic development, and muscle contraction. In these processes, forces generated at the molecular level by motor proteins are transmitted by disordered fiber networks, resulting in large-scale active stresses. While these fiber networks are well characterized macroscopically, this stress generation by microscopic active units is not well understood. Here we theoretically study force transmission in these networks, and find that local active forces are rectified towards isotropic contraction and strongly amplified as fibers collectively buckle in the vicinity of the active units. This stress amplification is reinforced by the networks' disordered nature, but saturates for high densities of active units. Our predictions are quantitatively consistent with experiments on reconstituted tissues and actomyosin networks, and shed light on the role of the network microstructure in shaping active stresses in cells and tissue.