Origin of slow stress relaxation in the cytoskeleton

TL;DR

This paper investigates how the interplay of nonlinear stress response and crosslinker dynamics in the cytoskeleton causes slow stress relaxation, resembling glassy behavior, with implications for cell mechanics.

Contribution

It combines rheology experiments and theoretical modeling to reveal the origin of slow stress relaxation in the cytoskeleton due to transient crosslinking and internal stress.

Findings

Slow stress relaxation similar to glass transition dynamics.

Nonlinear stiffening and crosslinker dynamics explain cell rheology.

Weak frequency dependence of shear modulus observed.

Abstract

Dynamically crosslinked semiflexible biopolymers such as the actin cytoskeleton govern the mechanical behavior of living cells. Semiflexible biopolymers nonlinearly stiffen in response to mechanical loads, whereas the crosslinker dynamics allow for stress relaxation over time. Here we show, through rheology and theoretical modeling, that the combined nonlinearity in time and stress leads to an unexpectedly slow stress relaxation, similar to the dynamics of disordered systems close to the glass transition. Our work suggests that transient crosslinking combined with internal stress can explain prior reports of soft glassy rheology of cells, in which the shear modulus increases weakly with frequency.