Strain Stiffening Induced by Molecular Motors in Active Crosslinked Biopolymer Networks

We have studied the elastic response of actin networks with both compliant and rigid crosslinks by modeling molecu-lar motors as force dipoles. Our finite element simulations show that for compliant crosslinkers such as filamin A, the network can be stiffened by two orders of magnitude while stiffening achieved with incompliant linkers such as scruin is significantly smaller, typically a factor of two, in excel-lent agreement with recent experiments. We show that the differences arise from the fact that the motors are able to stretch the compliant crosslinks to the fullest possible ex-tent, which in turn causes to the deformation of the fila-ments. With increasing applied strain, the filaments fur-ther deform leading to a stiffened elastic response. When the crosslinks are incompliant, the contractile forces due to motors do not alter the network morphology in a significan