**6. Applications of cold atmospheric plasma in medicine and healthcare**

CAP plasma can be employed in two different ways in biomedical applications. The first one is termed direct exposure or direct treatment, where plasma comes in direct contact with the biological sample to be treated. In this mode, all the plasma generated species, both long lived and short lived species, come in direct contact with the sample and work synergistically. The second mode is termed indirect exposure or indirect treatment. In this method, plasma is used to activate a liquid medium, and then the plasma activated liquid (PAL) is used for treatment. In this case, only the long lived chemical species such as nitrates, nitrites, and H2O2, which diffuse and solvate into the aqueous state, play a role. One advantage of PAL is that it can be stored and used at a later time and the composition may be tuned. Both types of CAP plasma treatment have shown significant success in biomedical applications. However, the amount of research reported using direct treatment is more than that using indirect treatment method.

Nowadays, CAP plasma has been successfully applied in various biomedical applications, including inactivation of microorganisms, sterilization of infected tissues, blood coagulation, skin regeneration, tooth bleaching, wound healing, cancer therapy etc. CAP plasma treatment for regenerative processes, such as wound healing, is one of the most advanced applications of plasma technology in the biomedical field. Three plasma devices have already been CE certified for medical use. The very first one is the medical device kINPen® MED (INP Greifswald/neoplas tools GmbH, Greifswald, Germany). The second one is PlasmaDerm® VU-2010 (CINOGY Technologies GmbH, Duderstadt, Germany), and the latest one is the SteriPlas medical device (Adtec Ltd., London, United Kingdom). Their specific purpose is wounds and skin diseases treatment. However, several more plasma devices are awaiting possible certification for clinical application [10, 42].

### **6.1 Use of CAP in disinfection, wound healing and dermatology**

In the beginning, CAP plasma in medicine was applied to the treatment of chronic wounds [43]. Isbary et al. in 2012 first reported about the clinical trials *Cold Atmospheric Pressure Plasma Technology for Biomedical Application DOI: http://dx.doi.org/10.5772/intechopen.98895*

of CAP plasma treatment on chronic ulcer wounds [44]. The authors reported significant infection reduction without any side effect. After that, several clinical trials have proven that CAP plasma action sufficiently reduces the bacterial load on wounds and improve chronic ulcer healing [42]. CAP treatment is also found to accelerate the rate of wound closure at early stages after wounding. Various studies have shown that CAP plasma is an effective tool for disinfection of a variety of bacteria and fungi on the skin and wound pathogens such as Methicillin-resistant *Staphylococcus aureus* (MRSA), *Escherichia coli*, *Pseudomonas aeruginosa* etc. [45].

Besides wound healing, the CAP plasma has also been investigated in dermatological applications. These include treatment of infective and inflammatory skin diseases like atopic eczema herpes, zoster, athlete's foot, acne and others [42, 45]. Some studies have reported positive effects of CAP plasma, but still, more research is required to understand the biochemical processes involved in dermatological applications.

### **6.2 Use of CAP plasma in cancer therapy**

Another most exciting and promising area of CAP plasma application in medicine is cancer treatment. Cancer cells appear to be more vulnerable to CAP plasma than healthy cells. Researchers have shown that CAP plasma can induce programmed cell death (apoptosis) in cancerous cells while leaving their nearby healthy cells essentially unaffected. Up until various *in vitro* and *in vivo* studies have been performed to study the CAP plasma effect on different cancer cells. These studies have repeatedly shown the anti-cancer capacity of CAP plasmas.

It has been reported that CAP plasma treatment increases intracellular ROS concentration. This, in turn, creates a severe redox imbalance in cancer cells as they are already under oxidative stress. Then, the redox imbalance leads to mitochondrial dysfunction, DNA damage, advanced state of oxidation of proteins, caspase activation, etc., and ultimately leads to death of cancer cells [11].

The early animal studies performed had shown the promising potential of CAP plasma in cancer therapy [46, 47]. Since then, many *in vivo* studies have been conducted, and similar positive results have been reported for various types of cancer cells injected under the skin of mice. To date, CAP plasma treatment has demonstrated a significant anti-cancer effect on approximately twenty cancer types *in vivo*. These cancer cell lines include skin, brain, head and neck, breast, leukemia, hepatoma, colorectal, bladder, cervical, lung etc. [48]. In 2019, Metelmann et al. reported the first clinical trials on patients with advanced head and neck cancer [49]. The trial demonstrated the clinical relevance of CAP plasma in cancer treatment and reported an overall positive effect. Some other researchers have shown that some radiation-resistant and chemo-resistant cancer cells are also sensitive to plasma treatment. Some studies have demonstrated CAP plasma as an intraoperative adjuvant treatment. It can be used to inactivate the remaining cancer cells after a surgery [42, 50]. In the USA, the Food & Drug Administration (FDA) approved the first clinical trials of CAP plasma to treat the cancer tumors remaining after surgery in 2019 [11].

### **6.3 Use of CAP plasma in dentistry**

Another long time studied field of CAP plasma application is in dental medicine. The most predominant oral diseases are caries and periodontitis, which are initiated by dysbiotic biofilms. The application of plasma primarily aims to reduce these biofilms on tooth substances and surrounding tissues. Also, instead of using an antimicrobial solution to oral cavity sites for disinfection, CAP plasma treatment can eliminate the unpleasant side effects from anti-microbial solution use. There

is a broad spectrum of research going on the possible oral and dental application of CAP plasma ranging from disinfection of root canals, inactivation and removal of biofilm on teeth, treatment of infections and wounds of oral mucosa, dentures and on dental implants, tooth whitening, decontamination and coating of dental prosthesis, cleaning and optimization of tooth and implant surfaces to improve bonding of dental fillings [10, 42].

## **6.4 Use of CAP plasma in other biomedical areas**

Another field explored from the beginning of plasma medicine research is CAP plasma use for hemostasis and blood coagulation [42]. Application of CAP plasma leads to blood coagulation in a much localized manner without damaging the tissue. Therefore it can be a valuable supporting technique in surgery. Aside from these large fields, the potential of CAP plasma in ophthalmology [51, 52] and neurology [53, 54] is also under investigation.
