## 4 Non-Thermal Plasma
These are SteriPlas (AdTec Ltd., Japan), PlasmaDerm (Cinogy GmbH, Duderstadt, Germany), and PlasmaOne (Medical Systems GmbH, Bad Ems, Germany) [64]. These plasma sources and several others have been used in various biomedical applications such as wound healing and chronic leg ulcers [66; 67], reducing bacterial populations in wounds [68], and biofilm decontamination or sterilization [69; 70]. Plasma has enormous potential in several biomedical research areas including sterilization of implant surfaces, surface modification [71], in-vitro blood coagulation [72; 73], wound healing and disinfection [74; 75], tissue regeneration [39; 73], treatment of various infections [39], bacterial decontamination and sterilization [69; 76; 77], dental cavities [78; 79], and cancer treatment [80; 81; 82]. The methods used for plasma generation are DBD, atmospheric pressure plasma jet (APPJ), plasma needle, and plasma pencil [83]. These plasmas can be produced in air or with various gases, such as oxygen, helium, argon, and nitrogen. Plasma can be produced by power sources with different frequencies such as low frequency, radio frequency, microwave frequency, high voltage AC or DC, to generate atmospheric and low-pressure glow discharge, corona, magnetron, microwave, gliding arc, plasma jet, and DBD discharge [84; 85; 86]. DBD has been known for more than a century. Floating-electrode dielectric barrier discharge (FE-DBD) is a DBD-based plasma source that is regarded as the starting point of modern plasma medicine [87]. FE-DBD is an electrical discharge between two electrodes at atmospheric pressure and air where one electrode is grounded, and the other is supplied with a high voltage (Figure 2). The high voltage electrode is enclosed within a dielectric material that limits the discharge current and the formation of an arc. Different dielectric materials used are quartz, glass or silica glass, polymers, ceramics, thin enamel, or polymer layers that block DC current [88]. The distance between the two electrodes ranges from micrometers to centimeters depending on the operating voltage, process gas and the plasma configuration employed [89]. DBD are usually operated at frequencies up to several tens of kHz. Two DBD configurations that have been employed for most of the applications are parallel and concentric configurations. The operating principle of DBD is shown in Figure 3a-d below. Three different types of DBDs are filamentary, patterned, and diffuse DBD [90]. These DBD types depend upon the construction and operating conditions of the plasma sources. Figure 2: Parallel and concentric dielectric barrier discharge (DBD) configurations [91]. Plasma jet is another type of NTP configuration. It is a tube with electrodes which are either placed inside or around it, through which gas flows and ionizes when it is subjected to the electrical field between the electrodes [92]. Figures 4b and 5b show the pictorial representations of volume DBD and jet plasma. In volume DBD, plasma is ignited in the gap between the high voltage electrode and the sample that is connected to the ground electrode. Whereas in the jet configuration, plasma is ignited inside the nozzle/tube and transported outside the object to be treated by a gas flow [93]. Usually, the DBD plasma uses atmospheric air as the working gas, while jet plasma uses different working gases such as helium, nitrogen, argon, oxygen, etc. Different types of plasma jets can be designed with various electrode configurations, working gases and applied electrical parameters [94].