Determination of RONS distribution on KI-starch agar-based tissue model generated by cold atmospheric pressure plasma

Abstract

Plasma Medicine has been considered one of the most challenging fields of interdis- ciplinary research. Not only the complexity of an electrically mutual-interaction system of Plasma Physics, but also its highly dynamic boundaries with biological subjects involv- ing branches of chemical reactions have opened a broad range of plasma-assist biomedical applications. Reactive oxygen and nitrogen species (RONS) have been proposed to play a vital role in plasma-biological interactions and can be effectively generated by cold atmo- spheric pressure plasma (CAP). Due to its dose-dependent effects leading to biochemical mechanisms, challenging questions have been raised on how to quantitatively control and deliver plasma-produced species to the target. Although numerical-approach models pro- vided more insightful information on RONS generated as well as transported, it is still limited to clearly describe certain well-defined conditions which are relatively unpractical for specific applications. Thus, a more practical experiment is essentially needed to fulfill this missing gap. In this work, an artificial tissue model made of agar mixed with KI-starch reagent is used. Spatial distribution of RONS impinged by atmospheric pressure plasma jet (APPJ) device is optically investigated by means of KI-starch-colored redox reaction. The oxidative potential of iodine, which is derived from KI-starch reagent, is lower than most of the common RONS so it is able to chemically react and depict a whole-picture effect of plasma on biological-like material in a single measurement. The plasma jet was operated under different conditions, for example, treatment time, working gas, and gap distance. The plasma-induced colored distribution was analyzed by time-series imaging to extract post- treatment features such as coverage area and diffusive behavior. This paves a way to design and optimize treatment protocol to achieve desirably plasma-biomedical effects. Moreover, the application of antimicrobial effects of pretreated tissue model against E.coli bacteria was also investigated. The distribution patterns revealed the contribution of operating gas which involves the dominant plasma-generated species. Meanwhile, the gap distance affected not only the transport of RONS in terms of short-lived and long-lived species, but also flow dy- namics of species before reaching the target. Due to the complexity of accumulated effects on the distribution pattern, the post-treatment characteristics have been systematically investigated by image analysis. The possible dominant RONS were finally proposed based on the integration of the experimental characteristics with literature reviews.