Evaluation strategies for risk assessment and usability of medical plasma sources in dermatology
This body of work provides descriptions of test systems, which can be used for a detailed assessment of physical, non-thermal atmospheric pressure plasma (APP) devices with regard to bio-medically relevant performance parameters. To establish and perform experiments, two different plasma sources were used: the plasma jet type kINPen® MED and a µs-pulsed volume dielectric barrier discharge (DBD) device. On the basis of a general physico-technical characterization of the two sources, evaluation strategies were developed to comparatively study (1) immediate cell damages after APP treatments and (2) to test if APPs cause genetic alterations in cellular DNA. Since the dermatological use of APP devices was of major interest in this thesis, different human skin fibroblast lines were used for plasma experiments. With the test systems, cell-type dependent effects of APP can be compared; moreover, a direct comparison of plasma-type dependent effects is also feasible. The first part of this thesis presents common test systems for the basic physical characterization, which include measurements of electric current, gas temperature and resulting thermal output, ultraviolet (UV) radiation, and emission of potentially unhealthy gases. Based on these measurements, a risk assessment was possible, which indicate that the two sources can be safely used as medical tools, but also exhibit plasma-specific handling and application requirements. Furthermore, a number of bio-medically relevant performance parameters of the sources were investigated: inactivation efficiency against pathogens, cytotoxicity on human skin fibroblasts, and chemical changes of plasma-treated phosphate buffered saline (PBS) solution. The results demonstrated that the impact of APPs on cells differ due to their different physical and chemical properties. Most, but not all, of the test systems presented here were published in the context of a cooperation with other groups as German DIN-Specification 91315. The second part of the thesis presents test systems for the assessment of long-term damages. The genotoxic and mutagenic effects of plasmas on isolated and cellular deoxyribonucleic acid (DNA) were examined with different techniques: host cell reactivation assay, DNA separation via gel electrophoresis, plasmid shuttle vector assay, and flow cytometry based on staining of phosphorylated histone proteins. The assessment of possible plasma-induced long-term damages is of utmost importance because some of the plasma components, like reactive oxygen species (ROS) and UV radiation, are well known to affect DNA. Particularly in dermatological therapies of wounds, potential mutagenic side effects induced by plasma application would lead to serious health risks, since the skin of patients will be directly exposed to plasma and, thus, also proliferative cells in the wound area. The level of impact of the two plasma sources on cells and isolated DNA was compared. At same treatment durations, plasma jet treatments usually induced stronger effects than DBD applications. In particular, a higher cytotoxicity and genotoxicity was observed. However, only a tendency towards a mutagenic effect was seen. In contrast, in experiments on plasmid DNA, which was located inside the cells during plasma treatments, no mutagenic effect was detected for either of the two sources. But, an increased formation of double strand breaks in genomic DNA could be demonstrated. Calculations of plasma doses within given treatment durations revealed that in same time periods the plasma jet transfers higher energy densities to the treatment object than the DBD plasma. On the other hand, the DBD plasma was shown to generate much higher ROS and RNS concentrations during the same treatment time. In some parts these findings can explain the observations in this thesis. It is, however, assumed that mainly ROS and UV radiation are responsible for the different effects of the two plasma sources. With the assays presented here, a valuable basis for a more detailed evaluation of different plasma jet systems and volume DBD devices with regard to their medical usability is created. Moreover, such APP sources can now be characterized and their desired therapeutic applications can be assessed on a standardized, quantitative basis.
Göttingen, Univ., Diss., 2017