Mechanical properties of intermediate filament networks under compression

Cell motility is a fundamental process that contributes to building and maintaining tissues as well as the progression of diseases such as fibrosis and cancer. The material properties of cells and tissues are a central feature of this process. The mammalian cytoskeleton is made up of a network of (semi-)flexible biopolymers, including actin, microtubules, and intermediate filaments. While the mechanical responses of fibrous biopolymer networks to shear deformation have been studied in great detail, their response to uniaxial loading remains poorly understood. Here, we study the mechanical response of reconstituted polymer networks comprised of the intermediate filament proteins vimentin and keratin using a parallel-plate rheometer. Our results indicate that reconstituted vimentin and keratin networks stiffen under axial compression, with cation concentration mediating network crosslinking. This stiffening contrasts with other biopolymer networks which compression soften but coincides with the compression stiffening behavior of cells themselves. These results motivate future work in cytoskeletal mechanics as well as the general phenomenon of compression stiffening in biopolymer environments.