Atmospheric Pressure Plasma Jet for Medical Therapy: Plasma Parameters and Risk Estimation

Plasma medicine as an independent medical field is emerging worldwide comparable to the development of laser technology years ago. The use of physical plasmas for bio-decontamination or sterilization [1-4], just as first surgical plasma applications such as argon-plasma coagulation [5,6] or coblation [7] are mainly based on lethal plasma effects on living systems. However, there is an additional huge potential of low temperature plasma application for therapeutic fields, which will be based on selective, at least partially non-lethal, possibly stimulating plasma effects on living cells and tissue [8-11]. An extremely promising field will be the plasma-based treatment of chronic wounds. A selective antimicrobial (antiseptic) activity without damaging surrounding tissue, combined with a controlled stimulation of tissue regeneration could revolutionize wound care. Other fields are tissue engineering, treatment of skin diseases, or tumor treatment based on specific induction of apoptotic processes. Several particular plasma applications in medicine as well as first clinical studies are focussed mainly on wound antiseptics and wound healing, skin diseases, and dental applications [11, 12-15]. Because these first practical applications have been interpreted to be very promising, a rapid grow of this new field plasma medicine has to be anticipated during the next time including the requirement of adjusted plasma sources for different applications. Because of the selectivity of plasma action needed, the performance parameters of the plasma sources have to be controlled in a very thoughtful manner. This is true not only with regard to the treatment efficiency concerning the intended therapeutic effect but also to potential risks connected with the direct plasma application at or in the human body. In contrary to indirect biological or medical plasma applications like antimicrobial treatments of medical products or surface modifications of implants, respectively, where also low-pressure plasma sources are used successfully, for direct treatment of living objects atmospheric-pressure plasma sources will be acceptable, only. Up to now, plasma sources for potential biological or medical applications are mostly characterized with regard to special biologic effects, e.g. antimicrobial efficiency, cell manipulation, or blood coagulation, which are related to potential therapeutic features. Naturally, this is the correct way to estimate the spectrum of potential medical plasma application and also to estimate specific adverse or toxic side effects in the close cell and tissue environment. But, furthermore the estimation of general risk factors is at least that much important to clarify minimum standards for plasma sources to allow it for direct medical applications and for comparison of different sources. From the present point of view such risk factors are plasma temperature, power transfer from the plasma, UV radiation, radicals and the generation of toxic gases and its release into the adjacencies which could be dangerous for patients or therapists. Additional potential risk factors not covered in this paper are electromagnetic fields of