# Uncovering the dynamic precursors to motor-driven contraction of active gels

## TL;DR

This study investigates the microscopic dynamics leading to contraction in active gels, revealing two precursors—gradual stress acceleration and sudden heterogeneous rearrangements—that precede macroscopic contraction.

## Contribution

It uncovers two novel microscopic precursors to gel contraction, enhancing understanding of active cytoskeletal dynamics beyond existing theories.

## Key findings

- Identified two dynamical precursors to gel contraction.
- Revealed heterogeneous and boundary-dependent rearrangements.
- Established analogy with passive gel rupture under load.

## Abstract

Cells and tissues have the remarkable ability to actively generate the forces required to change their shape. This active mechanical behavior is largely mediated by the actin cytoskeleton, a crosslinked network of actin filaments that is contracted by myosin motors. Experiments and active gel theories have established that the length scale over which gel contraction occurs is governed by a balance between molecular motor activity and crosslink density. By contrast, the dynamics that govern the contractile activity of the cytoskeleton remain poorly understood. Here we investigate the microscopic dynamics of reconstituted actin-myosin networks using simultaneous real-space video microscopy and Fourier-space dynamic light scattering. Light scattering reveals rich and unanticipated microscopic dynamics that evolve with sample age. We uncover two dynamical precursors that precede macroscopic gel contraction. One is characterized by a progressive acceleration of stress-induced rearrangements, while the other consists of sudden rearrangements that depend on network adhesion to the boundaries and are highly heterogeneous. Our findings reveal an intriguing analogy between self-driven rupture and collapse of active gels to the delayed rupture of passive gels under external loads.

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Source: https://tomesphere.com/paper/1812.06484