Chemomechanics Underpinning the Growth and Strengthening Behaviors of Mechanoresponsive Self-Growing Hydrogels

Living tissues, such as skeletal muscles, are capable of remodeling and self-growth in response to their mechanical environment. In contrast, synthetic materials, once formed, have little ability to grow and reconstruct. Recently, mechanoresponsive self-growing hydrogel, a novel hydrogel that can grow under mechanical stresses, has been reported. However, the chemomechanics underpinning the growth and strengthening behaviors of mechanoresponsive self-growing hydrogels remains largely unexplored. Here, we present a chemomechanical model for mechanoresponsive self-growing hydrogels by developing and integrating theories of mechanoradical generation due to chain rupture, chemical kinetics of polymerization, and new network formation. The chemomechanical model is applied to theoretically investigate the concentration of mechanoradical generated by stretching hydrogels, the polymerization kinetics of monomers and cross-linkers, and the strengthened mechanical behavior of self-growing hydrogels due to new network formation. Finally, we employ the theory to predict the stress–stretch responses of self-growing hydrogels under repetitive loading–unloading and growth cycles in the closed system. The results, especially the predicted ultimate stresses of the hydrogel over cycles, agree well with experimental measurements made by Matsuda et al. and can consistently explain the experimentally observed mechanical behaviors of self-growing hydrogels.