title: Determinants of fluidlike behavior and effective viscosity in cross-linked actin networks.
abstract: 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.
authors: Weldon School of Biomedical Engineering, Purdue University, West Lafayette, Indiana.
authors: Taeyoon
authors: T
authors: Kim
authors: Institute for Biophysical Dynamics, James Franck Institute, and Department of Physics, University of Chicago, Chicago, Illinois. Electronic address: gardel@uchicago.edu.
authors: Margaret L
authors: ML
authors: Gardel
authors: Institute for Biophysical Dynamics, Computation Institute, and Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, Illinois. Electronic address: emunro@uchicago.edu.
authors: Ed
authors: E
authors: Munro
mesh_terms: D051344:Actin Capping Proteins / Q000737:chemistry* / Q000378:metabolism; D008841:Actin Cytoskeleton / Q000737:chemistry* / Q000378:metabolism; D000199:Actins / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D004548:Elasticity; D006801:Humans; D056004:Molecular Dynamics Simulation; D058105:Polymerization; D014783:Viscosity
chemical_list: D051344:Actin Capping Proteins; D000199:Actins