**5. Effects of CAP plasma on biomaterials**

The bactericidal property of plasma was first demonstrated in the mid-1990s, and that started a new research field combining plasma physics and medicine, i.e. plasma medicine [39]. From the very beginning, it was realized that the plasma generated reactive species play a pivotal role in the observed biological effects of CAP plasma. With time, our knowledge of the mechanism of plasma action on cells and tissues has started growing significantly. The basic understanding of the mechanisms of CAP plasma effects on biomaterials is crucial to establish plasma technology application in the biomedical field.

Notwithstanding the use of different plasma sources, working gases, microorganism stains, cell types etc., some general biological plasma effects have been mentioned repeatedly in the basic research of plasma biomaterial interactions such as [9, 18]:

*Cold Atmospheric Pressure Plasma Technology for Biomedical Application DOI: http://dx.doi.org/10.5772/intechopen.98895*

	- a.Inactivation/killing of microorganisms
	- b.Inactivation or destruction of cells by initialization of apoptosis in mammalian cells
	- a.Stimulation of microorganism metabolism
	- b.Detachment of cells from the cell cluster
	- c.Influence on angiogenesis and cell proliferation and consequently promote wound healing and tissue regeneration
	- d.Influence on cell migration, expression of cell surface proteins

The possibility to inactivate microorganisms on sensitive surfaces of living structures like intact or wounded skin has attracted the very early interest of physicians. The *in vitro* and *in vivo* results of plasma assisted wound healing showed that plasma acts in a two-stage process. The first one is the antiseptic effect to restore the physiological potential of the wound area by decreasing bacterial load, and the next one is additional stimulation of the healing processes by tissue regeneration independent from antiseptic effects.

Based on the current state of knowledge on the mechanism of plasma biomaterial interaction, it can be deduced that the biological effects of CAP plasma are based on two principles:


The biologically important ROSs include superoxide (*O*<sup>2</sup> <sup>−</sup> •), hydrogen peroxide ( *H O*2 2 ), hydroxyl radical (•*OH* ), singlet oxygen (1 *O*<sup>2</sup> ), ozone (*O*<sup>3</sup> ) etc. The RNSs include nitric oxide (• *NO* ), nitrogen dioxide (• *NO*<sup>2</sup> ), nitrogen trioxide ( *NO*<sup>3</sup> ), peroxynitrite (*ONOO* −) etc. [7]. These reactive species are formed either by plasma–liquid interaction or by plasma–air interaction. These reactive species act on cells and tissues in the same way as that occur in the body's regular biochemical and physiological processes [40]. Based on this fundamental insight, the field of redox biology can now be used to explain the biological plasma effects. For example, hydroxyl radical causes peroxidation of unsaturated fatty acids present in lipids constituting the cell membrane. The strong oxidative properties of hydrogen peroxide affect proteins, lipids and DNA. Nitric oxide is known to affect the regulation of collagen synthesis, cell proliferation, regulation of immune deficiencies, induction of phagocytosis and angiogenesis etc. In cancerous cells, it is suspected that the action of CAP plasma increases intracellular ROSs, which can lead to cell cycle arrest at the S-phase, DNA breaks, and induction of apoptosis (programmed cell death). Researchers have also shown that the plasma generated ROS and RNS can penetrate biological tissues up to more than 1 mm depth.

Therefore they can interact with the cells on the surface as well as with those beneath [41]. As these ROSs and RNSs regularly occur in cell biological processes, mammalian cells have mechanisms to protect themselves from over-concentration of these species, which might otherwise lead to oxidative stress with severe biological consequences such as genotoxic DNA changes. Detailed investigations till now indicate that the application of CAP plasma does not increase the risk of genotoxicity [6].

Other plasma components such as UV radiation, electric field/electric current also play an additional role. However, the role of UV in direct biological effects is estimated to be very low due to the low dose of UV in these plasma devices. But its supporting role in reactive species generation is essential. Electric fields or currents have varying direct biological effects on living tissue, and it strongly depends on the type of discharge. The magnitude of these electric fields can be as high as several kV/cm, and they are suspected of playing a part, such as in cellular electroporation, which may help larger molecules to enter the cells. Besides these, the plasma generated charged species such as electrons and ions are also assumed to play some roles in the observed biological effects. More research is needed to identify the role of these plasma components for their possible part in biological and medically relevant plasma action, above all reactive species.
