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.
Contents
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'.
Applications
Plasma medicine can be subdivided into three main fields:
- Non-thermal atmospheric-pressure direct plasma for medical therapy
- Plasma-assisted modification of bio-relevant surfaces
- Plasma-based bio-decontamination and sterilization
Non-thermal atmospheric-pressure plasma
One of challenges is the application of non-thermal plasmas directly on the surface of human body or on internal organs. Whereas for surface modification and biological decontamination both low-pressure and atmospheric pressure plasmas can be used, for direct therapeutic applications only atmospheric pressure plasma sources are applicable.
The high reactivity of plasma is a result of different plasma components: electromagnetic radiation (UV/VUV, visible light, IR, high-frequency electromagnetic fields, etc.) on the one hand and ions, electrons and reactive chemical species, primarily radicals, on the other. Besides surgical plasma application like argon plasma coagulation (APC), which is based on high-intensity lethal plasma effects, first and sporadic non-thermal therapeutic plasma applications are documented in literature. However, the basic understanding of mechanisms of plasma effects on different components of living systems is in the early beginning. Especially for the field of direct therapeutic plasma application, a fundamental knowledge of the mechanisms of plasma interaction with living cells and tissue is essential as a scientific basis.
Mechanisms
Though many positive results have been seen in the experiments, it is not clear what the dominant mechanism of action is for any applications in plasma medicine. The plasma treatment generates reactive oxygen and nitrogen species, which include free radicals. These species include O, O3, OH, H2O2, HO2, NO, ONOOH and many others. This increase the oxidative stress on cells, which may explain the selective killing of cancer cells, which are already oxidatively stressed. Additionally, prokaryotic cells may be more sensitive to the oxidative stress than eukaryotic cells, allowing for selective killing of bacteria.
It is known that electric fields can influence cell membranes from studies on electroporation. Electric fields on the cells being treated by a plasma jet can be high enough to produce electroporation, which may directly influence the cell behavior, or may simply allow more reactive species to enter the cell.
The role of the immune system in plasma medicine has recently become very convincing. It is possible that the reactive species introduced by a plasma recruit a systemic immune response.