Figure 5.

Intrinsic nonlinear stretch modulus of fibrin fibers. (A) Stress-stiffening curves measured for different polymer concentrations, rescaled by protofibril density. The data collapse onto a mastercurve at large strain, where the network elasticity is governed by stretching of fibers with a nonlinear stretch modulus. The stiffening is consistent with the response of a wormlike chain (dashed line). (B) Stress-stiffening curves predicted for fibrin concentrations of 0.3 (low), 1, 3, and 9 (high) μM. (Inset) The fibers are modeled as loose, parallel arrays of protofibrils that fluctuate independently over a length l₀ = 0.1 μm between cross links to the rest of the fiber. The model combines entropic elasticity of the fibers between network cross links (red line), and intrinsic fiber nonlinear stretching due to entropic elasticity of the protofibrils (blue line). The extension (or compliance) of these two contributions add (black line).