Feedback between plasma source and biological tissue*

In Plasma Medicine studies, the effect of non-thermal plasma (NTP) on biological targets is typically correlated with the amount of stable reactive oxygen and nitrogen species (RONS) produced in a liquid medium. However, no cause-and-effect relationships between specific NTP effector(s) and cellular mechanisms or outcomes have been identified yet. The effect of NTP on cellular redox mechanisms and the response of the biological target is overlooked in these investigations. When the target is a physical substrate, bulk properties like conductivity and dielectric constant change the plasma. Biological targets like cells are enclosed by a lipid membrane and are filled with electrically charged ions that confer biophysical properties like membrane capacitance and cytoplasm conductivity. They maintain an electrical potential difference across the membrane by actively pumping these charged ions. Furthermore, cellular biomolecules (e.g., enzymes) can degrade RONS or produce them in response to NTP exposure and possibly modify plasma characteristics. It is then conceivable that dynamic targets like biological cells, possessing electrical properties and the ability to handle RONS, interact with and influence plasma properties. The influence of electrical properties of cells on the physical properties of NTP is neglected in plasma medicine research. We will share our observations which strongly suggest that in addition to the chemical interactions between plasma and target, there is an electrical connection between the plasma source and target. The power delivered to the plasma depends on the overall circuit impedance which in turn, is affected by the electrical properties of the target. Therefore, the target can impact the power deposited in the plasma which then impacts plasma parameters and plasma chemistry in the gas phase. We make a case for studying the whole system as a single unit, in situ.