Figure 3.

Microtubules increase average resistive force and heterogeneity of force response. (A) Force curves are shown for all 25 measurements, i, of composites with tubulin molar fractions of ϕ_T = 0 (red), 0.5 (green), and 1 (purple). (B) Average force during strain, <F_i-avg>, for each composite (circles, left axis), as well as the corresponding percent range, Δ_avg = 100^∗(F_{i-avg_max} − F_{i -avg_min})/(2<F_i-avg>) (triangles, right axis) are shown as a function of ϕ_T (bottom axis) and ratio of microtubule mesh size to actin mesh size ξ_M/ξ_A (top axis). The dotted vertical line shows when the mesh sizes for both filaments are equal (ξ_M = ξ_A). (C) The coefficient of variation, C_V(x) = σ_F/<F_i(x)>, for each ϕ_T as a function of x, shows increasing microscale heterogeneity in the force response with more microtubules. (D) An illustration of an equimolar actin-microtubule composite (ϕ_T = 0.5) is shown. As depicted, the actin mesh size is ∼2× smaller than the microtubule mesh, with ξ_A = 0.6 μm and ξ_M = 1.1 μm. To see this figure in color, go online.