Mechanics of bundled semiflexible polymer networks

While actin bundles are used by living cells for structural
fortification, the microscopic origin of the elasticity of bundled
networks is not understood. Here, we show that above a critical
concentration of the actin binding protein fascin, a solution of
actin filaments organizes into a pure network of bundles. While the
elasticity of weakly cross-linked networks is dominated by the
affine deformation of tubes, the network of bundles can be fully
understood in terms of nonaffine bending undulations.