Metal-carbon dual network reinforced bismuth-based chitosan hydrogels for improved photoresponsiveness, antibacterial activity, and wound healing.

Photodynamic therapy (PDT) is widely recognized as an effective antimicrobial strategy that minimizes the risk of bacterial resistance. Exploiting the intrinsic properties of hydrogels to create a favorable microenvironment for wound healing, researchers integrated bismuth-based metal particles into a chitosan-polyvinyl alcohol gel matrix. Representative gel complexes after metal-gel networks (Bi-gel) and composites introduced by biomass-derived carbon (BC) immobilized by cross-linking are referred to as CP/BC@Bi. The incorporation of carbon created a dual-network that enhanced electron transfer at the Bi‑carbon heterojunction, reduced electron-hole recombination, and optimized photogenerated carrier separation and migration. In vitro experiments showed that the excessive reactive oxygen species (ROS) generated by CP/BC@Bi under visible light enhanced PDT-mediated antimicrobial efficacy, causing complete bacterial membrane disruption and biofilm inhibition. Additionally, the surface roughness and defects of CP/BC@Bi enhanced bacterial adhesion, promoting ROS-bacterial interactions and amplifying its antimicrobial effects. Notably, the inhibition rates for Escherichia coli and Staphylococcus aureus were found to be 96 % and 94 %, respectively. Biocompatibility was rigorously assessed through hemocompatibility, cytotoxicity, and post-healing tissue staining experiments, all of which confirmed the safety profile of the hydrogel. In vivo studies demonstrated that wounds treated with PDT-CP/BC@Bi exhibited significantly accelerated healing rates, substantial dermal tissue regeneration, and normalized levels of inflammatory markers. This work demonstrates the potential of the environmentally friendly, resistance-free photodynamic antimicrobial hydrogel dressing in wound healing while offering insights into optimizing Bi-based hydrogels.