The use of microwave plasma for sterilization is relatively new. The advantages of this method are the relatively low temperature, time-savings and its nontoxic nature, in contrast to traditional methods such as heat and gas treatment, and radiation. This study investigated the sterilization effects of microwave-induced argon plasma at atmospheric pressure on materials contaminated with various microorganisms, such as bacteria and fungi. A low-cost and reliable 2.45 GHz, waveguide-based applicator was designed to generate microwave plasma at atmospheric pressure. This system consisted of a 1 kW magnetron power supply, a WR-284 copper waveguide, an applicator including a tuning section, and a nozzle section. Six bacterial and fungal strains were used for the sterilization test. The results showed that regardless of the strain, all the bacteria used in this study were fully sterilized within 20 seconds and all the fungi were sterilized within 1 second. These results show that this sterilization method is easy to use, requires significantly less time than the other traditional methods and established plasma sterilization methods, and it is nontoxic. It can be used in the field of sterilization in medical and dental clinics as well as in laboratory settings.

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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 HO-releasing hydrogels as an active wound dressing with antibacterial properties for treatment of drug-resistant bacterial infection. In this study, HO was used for two major purposes: (1) in situ gel formation via a horseradish peroxidase (HRP)/HO-triggered cross-linking reaction, and (2) antibacterial activity of the hydrogel via its oxidative effects. We found that there were residual HO in the matrix after in situ HRP-catalyzed gelling, and varying the feed amount of HO (1-10 mM; used to make hydrogels) enabled control of HO 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 HO 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 HO-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 HO 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.

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