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 <i>S. aureus</i>. 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.