Bioinspired Ion-Mediated Repair Strategy for Irreversibly Covalently Cross-Linked Double-Network Hydrogels

Chemically cross-linked double-network (DN) hydrogels undergo irreversible softening and weakening after yielding due to internal fracture, which restricts their reusability. In contrast, many biological tissues can repair internal damage through ion-mediated metabolic process, such as the healing of bone fractures. Inspired by this phenomenon, we demonstrate that specific multivalent metal ions can repair chemically cross-linked DN hydrogels after yielding. Repair is achieved by soaking the yielded hydrogels in metal ion solutions, where strong coordination interactions between metal ions and sulfonate side groups of the first network reconnect broken chains after fracture. As a result, the repaired DN hydrogels not only regain their energy dissipation capacity but can even surpass the original samples. The repair efficiency is influenced by ion concentration, preyield strain, first-network cross-linking density, and second-network concentration. Furthermore, the incorporation of dynamic metal-coordination bonds transforms the originally elastic DN hydrogels into viscoelastic and self-recoverable materials, enabling them to endure continuous and variable loading. This repair strategy, achieved without altering the classical DN hydrogel composition, expands the application potential of a system previously regarded primarily as a model for theoretical studies.