Tough double network hydrogels with rapid self-reinforcement and low hysteresis based on homogeneous networks

Most tough hydrogels are reinforced by introducing energy dissipation mechanisms, but simultaneously realizing a high toughness and low hysteresis is challenging because the energy dissipation structure cannot recover rapidly. In this work, high mechanical performance highly entangled double network (HEDN) hydrogels without energy dissipation structure were fabricated, in which physical entanglements acted as the primary effective crosslinking in the first network. This free-sliding entanglement structure allows the hydrogel network to form a highly uniform oriented structure during stretching, resulting in a high tensile strength of ~ 3 MPa, a fracture energy of 8340 J m-2 and a strain-stiffening capability of 47.5 in the case of 90% water content. Moreover, almost 100% reversibility is obtained in the HEDN hydrogels via energy storage based on entropy loss. The highly entangled double network structure not only overcomes the typical trade-off between the high toughness and low hysteresis of hydrogels, but more importantly, it provides an insight into the application of entanglement structures in high-performance hydrogels.