Bioinspired Metal–Ligand Coordination for Tuning the Mechanical Properties and Antibacterial Activity of Dual-Cross-Linked Hydrogels

The coordination ratio between metal ions and ligands governs the density, strength, and dynamics of coordination bonds in metal-coordinated hydrogels. However, the relationship between coordination stoichiometry and hydrogel properties remains insufficiently understood. In this study, dual-cross-linked poly(histidine methacrylamide) (PHisMA)-Ni2+ hydrogels were fabricated by varying the HisMA:Ni2+ molar ratio, enabling precise regulation of network architecture, mechanical performance, and relaxation behavior. Remarkably, by tuning the HisMA:Ni2+ molar ratio, Ni2+ ions generated multidentate coordination with HisMA groups, yielding extraordinary mechanical reinforcement, achieving up to 75-fold higher fracture strength, 55-fold higher Young’s modulus, and 492-fold higher toughness. The hydrogels also exhibited strong strain-rate dependence, tunable viscoelasticity, extended relaxation time, excellent energy dissipation, and rapid recovery. Furthermore, the hydrogels displayed potent antibacterial activity against S. aureus. These findings establish the control of metal–ligand coordination ratio as an effective design principle for engineering dual-cross-linked hydrogels with tailored mechanical and antibacterial functionality, holding great promise for biomedical and wearable applications.