Nonlinear Mechanics of Biopolymer and Tissue-Mimetic Hydrogels

While biopolymer gels made of rigid polymers such as fibrin and actin filaments have been reported to exhibit softening under compression and stiffening under extension, tissues (commonly consisting of cells embedded in a biopolymer network) have been reported to behave in an opposite manner and exhibit stiffening under compression and softening under extension. These findings naturally raise the question of whether such asymmetric nonlinear elastic properties of biopolymer gels and tissues might result in significant differences in how these materials fail under extensional and compressive loading conditions. We investigate this problem by performing extension-based and compression-based fracture tests on model gel systems that that exhibit different asymmetry in their nonlinear elastic properties. We share early lessons learned from our investigation, which sheds light on the fracture properties in biological materials and engineering principles for designing such properties in synthetic soft materials.