Fluidization of Transient Filament Networks

Abstract

Stiff or semiflexible fi laments can be crosslinked to form a network structure with unusual mechanical properties, if the crosslinks at network junctions have the ability to dynamically break and re-form. The characteristic rheology, arising from the competition of plasticity from the transient crosslinks and nonlinear elasticity from the fi lament network, has been widely tested in experiments. Though the responses of a transient fi lament network under small deformations are relatively well understood by analyzing its linear viscoelasticity, a continuum theory adaptable for fi nite or large deformations is still absent. Here we develop a model for transient fi lament networks under arbitrary deformations, which is based on the crosslink dynamics and the macroscopic system tracking the continuously re-shaping reference state. We apply the theory to explain the stress relaxation, the shape recovery after instant deformation, and the necking instability under a ramp deformation. We also examine the role of polydispersity in the mesh size of the network, which leads to a stretched exponential stress relaxation and a diffuse elastic-plastic transition under a ramp deformation. Although dynamic crosslinks are taken as the source of the transient network response, the model can be easily adjusted to incorporating other factors inducing fluidization, such as fi lament breakage and active motion of motor crosslinks, opening a way to address cell and tissue activity at the microscopic level.