Exploiting the advantages of cationic copolymers and AgBr nanoparticles to optimize the antibacterial activity of chitosan.

Recently, the chitosan (CS)-based composites have attracted increasing attention for controlling and preventing the spread of pathogenic microorganisms. Herein, an amphiphilic copolymer containing epoxy and quaternary ammonium groups (PBGDBr) was synthesized via three common acrylate monomers. The epoxy groups of this copolymer were then crosslinked with the amino groups of CS to synthesize a natural/synthetic (PBGDBr-C) composite to increase the water solubility of CS under alkaline conditions and enhance its antibacterial activity based on chemical contact-type modes. Moreover, silver bromide nanoparticles (AgBr NPs)-decorated PBGDBr-C (AgBr@PBGDBr-C) composite was prepared, which aimed to endow the final AgBr@PBGDBr-C composite with a photodynamic antibacterial mode relying on the formation of Ag/AgBr nanostructures catalyzed by visible light on AgBr NPs. The results showed that the final composite possessed satisfactory bactericidal effects at concentrations higher than 64 and 128 μg/mL against Escherichia coli and Staphylococcus aureus, respectively. Additionally, The L929 cells treated with the final composite retained high cell viability (>80 %) at a concentration of 128 μg/mL, indicating its low toxicity to L929 cells. Overall, our synthetic strategy exploits a multi-modal system that enables chemical-photodynamic synergies to treat infections caused by pathogenic bacteria while delaying the development of bacterial resistance.