Fig. 4.

Force-dependent unbinding of fibers leads to strain–enhanced stress relaxation in fiber networks. (A) Schematic of the proposed mechanism underlying strain-enhanced stress relaxation. Under strain imposed during a stress relaxation test, fibers in the network are strained and exert a force resisting the strain determined by the fiber’s force–extension relaxation. These forces are transmitted through cross-link points linking the fibers together. It is hypothesized that the probability of unbinding or cross-link disassociation is force dependent, or a higher force leads to a greater probability of unbinding for a fiber. This is predicted to lead to strain-enhanced stress relaxation. Unbound fibers can rebind to the networks, contributing the elastic modulus again. Comparison of stress relaxation data from experiments (exp, dotted line) and the corresponding results from the computational simulations (sim, solid line) of (B) the entropic model and (C) the nonentropic model for various strains. Simulation results given the assumptions that there is no rebinding of fibers to the networks for (D) the entropic model and (E) nonentropic model or that the probability of binding is independent of the force for (F) the entropic model and (G) nonentropic model.