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 μm deep for low-power He-O ₂ plasma and this is closely correlated to the penetration of liquid-phase plasma chemistry dominated by O₂ ^-, H ₂O₂, and HO₂ or O₂ ^-, H₂O₂, and O₃. Optimization by manipulating liquid-phase chemistry is expected to improve the penetration depth to 40-50 μm. For direct plasma treatment of skin tissues at radio frequencies, the key tolerance issue is thermal injuries even with a tissue temperature <50 °C and these can lead to induction of pain and protein denaturation at a small discharge density of 8-15 mA/cm² 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.