Vimentin networks at high strains

The cytoskeleton is crucial in maintaining cell shape and structural integrity. It consists of three types of filaments, including actin filaments and intermediate filaments (IFs) that exhibit distinctly different force-strain behavior: while IFs show nonlinear behavior with exceptional extensibility and remarkable resistance against rupture at high strains, actin filaments break at low strains. Here we address the question of whether the intriguing mechanical behavior of vimentin IFs translates to the network scale. We apply high strains to in vitro reconstituted networks using optical tweezers and find contrastive behavior for the two cytoskeletal networks: vimentin networks show strain stiffening behavior and respond in an elastic, solid-like manner with high forces opposing the active movement of the beads, whereas actin networks strain soften and fluidize at low forces. Our work highlights the complementary nature of the components of the cytoskeleton, which -- in the cell -- are partly co-localized and believed to constitute a composite biological material.