Cross-linked biopolymer networks with active motors: Mechanical response and intra-network transport

Abstract

Cross-linked biopolymer networks are widespread in the cytoskeleton of cells and biological gels, which are responsible for maintaining the structural integrity of the cells/materials as well as generating forces to drive cellular movement. Microscopically, these networks are composed of randomly distributed semi-flexible filaments along with the associated cross-linking and motor proteins that are under constant external and internal stresses. In the present study, we developed a computational model based on Langevin dynamics to examine the mechanical response of such networks where the bending and stretching of individual biopolymers, deformation and breakage of cross-linkers and the active role of molecular motors have all been considered. It was found that pronounced strain stiffening took place with increasing imposed shear deformation. However, such stiffening effect under shear was attenuated by the successive rupture of cross-linkers. Interestingly, the appearance of motor-induced contractile forces within the networks significantly increased their apparent modulus in the entropy-dominated regime (i.e., at small strains). In addition, considerable bundling and re-alignment of filaments were also observed under the contraction by motor proteins, in agreement with experimental observations. Finally, the fluctuating forces generated by active motors were found to contribute to the enhanced diffusion of nanometer-sized particles within the network. © 2019 Elsevier Ltd