Slide-Ring Cross-Links Mediated Tough Metallosupramolecular Hydrogels With Superior Self-Recoverability

Stiff yet recoverable water-containing materials can be found in many biological tissues including tendons, cartilages, and skins. However, it remains a challenge to develop hydrogels as load-bearing materials where high stiffness and toughness, as well as fast recoverability, are required. Making framework more compact with more rigid chains could make a gel stiffer but also restrict its recovery for lower chain mobility. Here, we report a rigid yet recoverable hydrogel by incorporating polyrotaxane into a physically cross-linked network with movable slide-ring (SR) as the chemically anchoring point. The dynamic and robust carboxyl-Fe3+ coordination bonds endow the gel with high stiffness and potential to recovery, while SR structures within the framework act as pulleys to equalize the distribution of stress and activate the reattachment of dynamic bonds. The obtained gel possesses a tunable Young's modulus up to 18.3 MPa, comparable to that of natural cartilage. More notably, SR gel exhibits faster recovery than the reference gel with fixed cross-links, as confirmed by analyzing their stress relaxation behaviors using a three-dimensional continuum model. This work provides an innovative and practical strategy for designing rigid yet recoverable hydrogels with high strength and toughness, which can be further applied to other systems containing dynamic bonds.