Low temperature atmospheric plasmas for biomedical applications

DoctorLow temperature atmospheric pressure plasmas (LTAPPs) have been of great interest to investigate characterization of plasmas and various useful applications such as wound healing, cancer treatment, teeth whitening, skin care etc. In LTAPPs, there are various gas plasmas such as Helium (He), Argon (Ar), Air, nitrogen (N2), Oxygen (O2) and so on. Among these gaseous plasmas, He, Ar, Air plasmas are representative for atmospheric pressure plasma. These plasmas are investigated about the characterization and applied for wound healing. First, we researched Ar atmospheric pressure plasma. Using Ar/Air mixture microwave plasma, we investigated the effects of air and gas temperature on the generation of electrons, ozone (O3), and nitric oxide (NO) through experiments and chemical kinetics simulation. The global model (GM) chemical kinetics simulation was used to validate and complement experimental observations. As the air percentages in Ar plasma increase, electrons are mainly generated by reactive oxygen species (ROS), but electron densities decrease. This is why plasma jet length becomes shorter with the mixture of air to Ar plasma at the same power. The profile of O3 density has a maximum point because these are affected by O2 molecules and gas temperature. O3 density increases because these are generated via recombination of atomic oxygen (O) and O2 radicals as the air percentage increases. As the gas temperature increases, O3 densities decrease and O3 radicals are mainly destroyed by ROS such as O2, excited O2, and O, although air percentage increases. NO radicals increase continually with the addition of air mixture and increase with gas temperature. With respect to biomedical applications, in the case of Ar/Air plasma treatment, it takes just 2 days, which has reduced the wound area to 30% because of faster scab formation over the wound and mRNA activation. Abundant NO radicals with ROS in Ar/Air plasma strongly enhance IL-6 and TGF-β1, which facilitate collagen remodeling and wound recovery effectively. Second, we investigated He atmospheric pressure plasma. We elucidated the processes through which the pH level in the solution is changed from neutral to acidic after plasma exposure and key components with pH and air variation. The pH level in a liquid solution is changed by He+ and He(21S) radicals. Hydroxyl radicals (OH, H2O2, HO2) and NO radicals increase as the pH level decreases (e.g., pH 4). O3 density decreases when pH level in the solution decreases and air concentration decreases. It can be a method of removing O3 that can cause chest pain and damage on lung tissue when the density is very high. H2O2, HO2 and NO radicals are found to be key factors for cell inactivation in the solution with pH and air variation. When air percentage in He plasma increases at same pH level, excited O2, O3, O2-, H2O2, HO2, and NO radicals increase. Especially the density of O2- is 1,000 times lower than other species. With pH and air effects, we insist that H2O2, HO2, and NO radicals are key for strong sterilization because densities of these radicals increase as the pH level decreases and air percentages increase. Third, we investigated air atmospheric pressure plasma. Using surface type air atmospheric pressure plasma, we investigated the amount of O3 and other reactive species generation with variations of the surface temperature of an electrode through an optical emission spectrum and a tube type gas detector. Reduced version of global model (r-GM) was employed to complement these experimental observations. The results of the model matched well with the experimental data. The amount of O3 generated from the surface type air plasma device is dramatically reduced with increasing gas temperature. However, the amount of O and NO radicals increases proportionally with high temperature. It is helpful because these radicals are important agents for biomedical applications. We also elucidated the dominant reaction related to the generation or loss of these radicals based on temperature variation through our GM. With these results about Ar, He, Air LTAPPs, the plasma characterization and effect on wound healing for biomedical application was analyzed