Plasma medicine

Plasma medicine is an emerging field that combines plasma physics, life sciences and clinical medicine. It is being studied in disinfection, healing, and cancer. Most of the research is in vitro and in animal models.

It uses ionized gas (physical plasma) for medical uses. Plasma, often called the fourth state of matter, is an ionized gas containing positive ions and negative ions or electrons, but is approximately charge neutral on the whole. The plasma sources used for plasma medicine are generally low temperature plasmas, and they generate ions, chemically reactive atoms and molecules, and UV-photons. These plasma-generated active species are useful for several bio-medical applications such as sterilization of implants and surgical instruments as well as modifying biomaterial surface properties. Sensitive applications of plasma, like subjecting human body or internal organs to plasma treatment for medical purposes, are also possible. This possibility is profoundly being investigated by research groups worldwide under the highly-interdisciplinary research field called 'plasma medicine'.

Plasma sources used in plasma medicine are typically "low temperature" plasma sources operated at atmospheric pressure. In this context, low temperature refers to temperatures similar to room temperature, usually slightly above. There is a strict upper limit of 50 °C when treating tissue to avoid burns. The plasmas are only partially ionized, with less than 1 ppm of the gas being charged species, and the rest composed of neutral gas.

Dielectric-barrier discharges are a type of plasma source that limits the current using a dielectric that covers one or both electrodes. A conventional DBD device comprises two planar electrodes with at least one of them covered with a dielectric material and the electrodes are separated by a small gap which is called the discharge gap. DBDs are usually driven by high AC voltages with frequencies in the kHz range. In order to use DC and 50/60 Hz power sources investigators developed the Resistive Barrier Discharge (RBD). However, for medical application of DBD devices, the human body itself can serve as one of the two electrodes making it sufficient to devise plasma sources that consist of only one electrode covered with a dielectric such as alumina or quartz. DBD for medical applications such as for the inactivation of bacteria, for treatment of skin diseases and wounds, tumor treatment and disinfection of skin surface are currently under investigation. The treatment usually takes place in the room air. They are generally powered by several several kilovolt biases using either AC or pulsed power supplies.

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