We will first report on the key role of conductive targets mimicking biological samples (such as those involved during in vitro, ex vivo and in vivo skin or skin cells), on most of the plasma characteristics during non-thermal plasma treatments. Drastic mutual influence of plasma jet and targets has been shown to induce critical modifications of: reactive species balance and densities, current amplitude, temperature, gas flow features when comparing with the situation of the so called “free jet expansion” in ambient air. This strong interplay between plasma and targets has to be considered before (gas flow impingement before plasma ignition) and during plasma delivery as a dynamic feature. Both plasma and targets may indeed encounter various continuous evolutions during plasma treatment such as: plasma source feed gas purity, plasma kinetics, target humidity, target electrical conductivity, thermal load, on target charge deposition, cell microenvironment modulation (oxygen level, plasma induced permeabilization) …
When translating results obtained during in vitro or preliminary skin sample experiments to clinical situation, one has also to account for the critical role of plasma nozzle to surface gap variation and of the skin specificity of individuals.
The first objective of our work is to try to achieve a safe, reproducible and individual-independent plasma delivery on human skin. This approach includes first the implementation of, as simple and user friendly as possible, diagnostics tools providing signals likely to be correlated with the plasma jet source operating parameters (voltage, repetition rate, gap distance). This requires to select the most sensitive in situ signals captured by diagnostics tools and then try to reach a “real time” modulation and loop controlled operation of the plasma source. This first task represents a prerequisite for the development of a safe and reliable plasma device likely to offer new opportunity for anti-aging issues or skin treatments in cosmetics or dermatology applications.
This work is supported by the research project PlasmaCosm-ARD 2020 Cosmetosciences, Région Centre Val de Loire.