Figure 6.

Relaxation of induced force is strongly suppressed as cross-linker ratio R increases. (A) Time evolution of induced force after the strain. (Solid black lines) Fits of the data to a sum of two exponential decay functions with well-separated decay times t_fast and t_slow. (Inset) Zoomed-in data for R < 0.07. (B) Measured force decay times, t_slow and t_fast (inset), as a function of R, determined from the corresponding fits in (A). (Dashed lines) Fits to exponential functions of cross-linker ratio R (t ∼ exp(R/R^∗)) with critical cross-linker ratios R^∗ listed in corresponding plots. (C) Terminal sustained force F_t, defined as the force reached at the end of the relaxation phase, as a function of R, with an exponential fit (dashed line) that gives R^∗ ≃ 0.007. (D) Ensemble-averaged retraction velocities $\langle v_x\rangle$ during the relaxation phase for filaments closest to the strain path (d = 9 μm) as a function of time for networks of varying R. (E) Retraction velocities immediately following the strain as a function of cross-linker ratio R. Velocities correspond to the data in the first time point of (D). Corresponding retraction distance for R = 0.07 was measured to be ∼0.5 μm, corresponding to 80% recovery of the strain-induced displacement (data not shown). To see this figure in color, go online.