Determinants of fluidlike behavior and effective viscosity in cross-linked actin networks

Biophys J. 2014 Feb 4;106(3):526-34. doi: 10.1016/j.bpj.2013.12.031.


The actin cortex has a well-documented ability to rapidly remodel and flow while maintaining long-range connectivity, but how this is achieved remains poorly understood. Here, we use computer simulations to explore how stress relaxation in cross-linked actin networks subjected to extensional stress depends on the interplay between network architecture and turnover. We characterize a regime in which a network response is nonaffine and stress relaxation is governed by the continuous dissipation of elastic energy via cyclic formation, elongation, and turnover of tension-bearing elements. Within this regime, for a wide range of network parameters, we observe a constant deformation (creep) rate that is linearly proportional to the rate of filament turnover, leading to a constant effective viscosity that is inversely proportional to turnover rate. Significantly, we observe a biphasic dependence of the creep rate on applied stress: below a critical stress threshold, the creep rate increases linearly with applied stress; above that threshold, the creep rate becomes independent of applied stress. We show that this biphasic stress dependence can be understood in terms of the nonlinear force-extension behavior of individual force-transmitting network elements. These results have important implications for understanding the origins and control of viscous flows both in the cortex of living cells and in other polymer networks.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin Capping Proteins / chemistry*
  • Actin Capping Proteins / metabolism
  • Actin Cytoskeleton / chemistry*
  • Actin Cytoskeleton / metabolism
  • Actins / chemistry*
  • Actins / metabolism
  • Animals
  • Elasticity
  • Humans
  • Molecular Dynamics Simulation*
  • Polymerization*
  • Viscosity


  • Actin Capping Proteins
  • Actins