In Situ Forming and H 2 O 2 -Releasing Hydrogels for Treatment of Drug-Resistant Bacterial Infections.

Various types of commercialized wound dressings (e.g., films, foams, gels, and nanofiber meshes) have been clinically used as a physical barrier against bacterial invasion and as wound-healing materials. Although these dressings can protect the wounded tissue from the external environment, they cannot treat the wounds that are already infected with bacteria. Herein, we report in situ H2 O2 -releasing hydrogels as an active wound dressing with antibacterial properties for treatment of drug-resistant bacterial infection. In this study, H2 O2 was used for two major purposes: (1) in situ gel formation via a horseradish peroxidase (HRP)/H2 O2 -triggered cross-linking reaction, and (2) antibacterial activity of the hydrogel via its oxidative effects. We found that there were residual H2 O2 in the matrix after in situ HRP-catalyzed gelling, and varying the feed amount of H2 O2 (1-10 mM; used to make hydrogels) enabled control of H2 O2 release kinetics within a range of 2-509 μM. In addition, although the gelatin-hydroxyphenyl propionic acid (GH) gel called "GH 10" (showing the greatest H2 O2 release, 509 μM) slightly decreased cell viability (to 82-84%) of keratinocyte (HaCaT) and fibroblast (L-929) cells in in vitro assays, none of the hydrogels showed significant cytotoxicity toward tissues in in vivo skin irritation tests. When the H2 O2 -releasing hydrogels that promote in vivo wound healing, were applied to various bacterial strains in vitro and ex vivo, they showed strong killing efficiency toward Gram-positive bacteria including Staphylococcus aureus, S. epidermidis, and clinical isolate of methicillin-resistant S. aureus (MRSA, drug-resistant bacteria), where the antimicrobial effect was dependent on the concentration of the H2 O2 released. The present study suggests that our hydrogels have great potential as an injectable/sprayable antimicrobial dressing with biocompatibility and antibacterial activity against drug-resistant bacteria including MRSA for wound and infection treatment.