High-Strength Tough Hydrogels with Tunable Fluorescent Response via Hydrophobic Interaction and Metal Coordination

In response to the known limitations of smart optical hydrogels, which suffer from poor mechanical properties and lack of antibacterial performance, we report a smart optical metallic hydrogel (Zn2+-P(AM-EMA-BMHPD)) with excellent elongation, antibacterial capability, and controllable fluorescence intensity. The solvent exchange method was successfully used to incorporate the diacylhydrazone-based hydrophobic cross-linker (BMHPD) into the hydrogel system, resulting in P(AM-EMA-BMHPD) hydrogels with dual chemical covalent and hydrophobic physical cross-linking. BMHPD serves as both a monomer and a cross-linking agent, reducing the use of functional monomers and further enhancing mechanical properties. The maximum tensile strain and stress are 515% and 1.76 MPa, respectively, with a maximum toughness of 5.11 MJ/m3. After complexation with Zn2+, the hydrogel exhibits blue fluorescence, with the fluorescence intensity increasing by 535% compared to before complexation. The incorporation of the acylhydrazone structure imparts excellent antibacterial properties to P(AM-EMA-BMHPD) hydrogels, with optimal inhibition rates of 62% and 98% against E. coli and S. aureus, respectively. Furthermore, based on the controllable regulation of Zn2+ by P(AM-EMA-BMHPD) hydrogels, an erasable fluorescence writing process was designed, which exhibits the ability to be repeated multiple times.