Role of fiber bending in the macroscopic active contraction of model cytoskeletal networks

Myosin motors in disordered actin networks produce contractile forces that drive cellular processes such as cell shape change and locomotion. The combined action of multiple myosin motors leads to macroscopic contraction of the actin gel, which typically occurs as a network of crosslinked elastic fibers. These fibers can undergo multiple deformation modes such as stretching, bending, and buckling, leading to a long-range and heterogeneous transmission of forces through the elastic network. We investigate the motor-driven macroscopic contraction of elastic fiber networks at different fiber bending rigidities. The network is modelled as a diluted triangular lattice with fixed boundaries, while the active stresses generated by myosin motors are modelled as isotropic contractile dipoles. We characterize the strain distribution and normal forces at the boundaries of the network for different configurations of dipoles. We find that networks with stiffer fibers show more force chains as well as higher normal forces at the boundaries, a measure of macroscopic network contraction. Thus, bending-dominated fiber networks under internal forces behave differently from conventional elastic materials under external compression. Our results may be compared to in vitro actomyosin network contraction, where the bending rigidity of actin bundles is varied by changing the concentration of bundling crosslinkers like fascin.