Elastic properties of vimentin networks

We measure the mechanical properties of in vitro networks of the intermediate filament protein vimentin by rheometry. Vimentin networks are highly elastic even for small volume fractions of protein and exhibit dramatic stiffening with strain. We find that divalent ions such as Ca2+ and Mg2+ act as effective cross-linkers in the vimentin network. The observed linear and nonlinear elastic responses at intermediate strains can be explained quantitatively by affinely stretching the entropic fluctuations of single semiflexible filaments; at high strains, enthalpic stretching of the individual filaments contributes to the observed nonlinear response.