Figure 3.

Viscoelastic response of actin networks with varying degrees of cross-linking (R = 0–0.07). (A) Average force exerted by actin networks to resist probe motion. (B) Elastic differential modulus K as a function of time as obtained from the derivative of the force in (A) with respect to stage position. All data shows initial stiffening to a maximum value (K_max) before softening and yielding to a terminal steady-state stiffness/elasticity (K_t). (C) Maximum differential modulus (K_max) follows an exponential function K_max ∼ exp(R/R^∗) with a critical cross-linking ratio of R^∗ ≃ 0.015. (D) Terminal modulus K_t versus R increases exponentially with R with R^∗ ≃ 0.018. (E) Yield time, t_y, defined as the time at which K(t) = K(0)/2e, displays a similar exponential dependence on R with R^∗ ≃ 0.009. To see this figure in color, go online.