Toxicity analysis of direct nonthermal plasma treatment of living tissue

Non-thermal dielectric barrier discharge plasma produced at normal atmospheric pressure and applied directly to living tissues is now being widely considered for various applications in medicine, viz; skin sterilization, wound treatment, treatment in malignant tissues and many others. One of the key questions that arise in this type of topical treatment is whether the skin remains undamaged after non-thermal plasma treatment. In this paper we study the possible short term and long term toxic effects of the non-thermal plasma treatment on intact living tissue. The results from the previous rodent model provided strong evidence for the ability of non-thermal plasma to sterilize the surface of the tissue without any visible or microscopic damage to the tissue. We evaluated the potential toxic effects of non-thermal plasma treatment on underlying skin cells and tissue on intact porcine skin, since it is well established that porcine (pig) skin closely resembles human skin. Based on prior knowledge that non-thermal plasma has non-damaging and damaging regimes, an experimental protocol based on the pig model was constructed. In a Yorkshire pig model, the intact skin treatment was carried out at varying doses to locate the damaging power/time (dose) combination and the resulting skin damage was analyzed. Once the dose where damage occurred was located, the treatment was stopped recording the power level and time of application. Then successively lower power levels were applied on different patches to find a dose (power/time) which was non-damaging for prolonged treatment times. The pig was kept alive for one day post treatment and the tissue samples were sectioned before euthanizing the animal. From the experiments we determined that a dose of 15 mins at a low power of 0.2 Watt/cm 2 caused no visible or microscopic damage to the tissue while a dose of 3 mins at high power of 1.0 Watt/cm 2 caused a second degree burn. These results were confirmed by histology staining. Of note is that sterilization is achieved in about 5 sec at a low power treatment of 0.2 Watt/cm 2 . Detailed analysis of any biochemical changes and inflammatory response initiation in the treated tissue will be carried out. In this paper we show that low power plasma treatment is non-toxic to intact pig skin.