Local Response of Actin Networks is Controlled by Tensile Strains in the Stress-Fibers: Insights From a Discrete Network Model

Abstract

Using a discrete random network model of the actin cytoskeleton, we studied the effect of stretching of a stiff-fiber on the elastic response of a fibrous network. In real networks, this component can either be a stress-fiber, bundle of fibers within the network, or a microtubule. We analyze the response of this network due to shear loads while the stiff component is under or free of tensile strains. It is observed that the initial response of this network under shear loading is highly dependent on the amount of tensile strain in the stiff-fiber. In addition, the response depends on the amount and the direction of the shear loading, which is either a softening or a stiffening response depending on the loading direction. As a result, the apparent shear modulus of the network containing a preloaded stiff-fiber may become larger or smaller compared to a network with a relaxed stiff-fiber. This effect intensifies for higher levels of tensile strains in the stiff-fiber and for stiffer cross-links, and lessens for higher network densities. The results of the current research are useful in deciphering the response of soft fibrous materials such as the cell cytoskeleton or other networks comprising a random fibrous network containing a stiffer component than the main fibers of the network.