A Model of Plasma-Biofilm and Plasma-Tissue Interactions at Ambient Pressure

This paper presents the development of a model framework for plasma-biofilm and plasma-tissue interactions that can link molecular simulation of plasma chemistry to functions at a cell population level or a tissue level. This is aided with a reactive penetration model for mass transfer of highly transient plasma species across the gas-liquid boundary and a panel of electrical and thermal thresholds considering pain sensation, protein denaturation and lethal electric currents. Application of this model reveals a number of previously little known findings, for example the penetration of plasma chemistry into highly hydrated biofilms is about 10-20 mu m deep for low-power He-O-2 plasma and this is closely correlated to the penetration of liquid-phase plasma chemistry dominated by O-2 (-), H2O2, and HO2 or O-2 (-), H2O2, and O-3. Optimization by manipulating liquid-phase chemistry is expected to improve the penetration depth to 40-50 mu m. For direct plasma treatment of skin tissues at radio frequencies, the key tolerance issue is thermal injuries even with a tissue temperature < 50 A degrees C and these can lead to induction of pain and protein denaturation at a small discharge density of 8-15 mA/cm(2) over few tens of seconds. These and other results presented offer opportunities to improve plasma-biofilm and plasma-tissue interactions. The model framework reported may be further extended and can be used to non-biomedical applications of low-temperature plasmas.