Mechanically reinforced black TiO₂ nanocomposite hydrogels with NIR-triggered photothermal/photodynamic antibacterial...

Polyvinyl alcohol (PVA)-based hydrogels hold great promise for biomedical applications but are hampered by limited mechanical strength and insufficient antibacterial efficacy. In this work, oxygen-deficient black titanium dioxide (BTiO₂) nanoparticles were incorporated into a chitosan/PVA matrix via a translation-oriented, chemical-crosslinker-free freeze-thaw strategy to construct a nanocomposite hydrogel. Serving as robust physical cross-linking nodes, the BTiO₂ nanoparticles densified the porous network, markedly reducing the average surface pore size from 62.5 μm to 31.4 μm, enhancing the storage modulus from 1.12 kPa to 1.97 kPa, and ensuring exceptional thermal stability up to 60 °C. Consequently, the hydrogel achieved a tensile strength of 230 kPa, representing a 248% improvement over pristine PVA, while regulating the equilibrium swelling ratio to an optimal 985% for effective wound exudate management. Furthermore, the nanocomposite demonstrated a controllable in vitro enzymatic degradation profile, retaining 87.8% of its mass over 7 days to provide sustained structural support. The introduction of BTiO₂ endowed the hydrogel with potent synergistic photothermal and photodynamic capabilities. Under 808 nm near-infrared (NIR) irradiation (0.5 W/cm²) for 5 min, the localized temperature rapidly reached a mild 45 °C with the simultaneous generation of both Type I and Type II reactive oxygen species (ROS). This propelled the antibacterial efficiency against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) to 98.6% and 99.0%, respectively. Crucially, despite this excellent biocidal activity, the hydrogel exhibited an extremely low hemolysis rate of 0.95%, actively supported HUVEC proliferation, and demonstrated strict biosafety without collateral phototoxicity. This work presents a mechanically robust, highly efficient, and exceptionally safe light-activated platform for advanced wound dressing applications.