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    Human health risk evaluation of a microwave-driven atmospheric plasma jet as medical device
    (Amsterdam [u.a.] : Elsevier, 2017) Lehmann, A.; Pietag, F.; Arnold, T.
    Purpose: The aim of this study was the characterisation of a microwave-driven atmospheric plasma jet (APJ) dedicated for medical applications. The scientific focus includes harmless sterilization of surfaces and therapeutic treatments in dentistry. Methodes: The plasma was investigated with respect to potential health risks for human beings, which could occur especially by the gas temperature, heat flow, patient leakage current, UV emission and ozone emission from the plasma jet, according to DIN SPEC 91315:2014-06 (General requirements for plasma sources in medicine) [1]. Results: The results of the experiments indicate a high potential of the plasma jet to be used as a medical device exhibiting low gas temperatures up to 34 °C. The calculated leakage currents are mostly below the 10 μA threshold. The limiting UV exposure duration for the APJ with a calculated maximum effective irradiance of 2.6 μW/cm2 is around 19 min, based on the exposure limits of the international commission on non-ionizing radiation protection guidelines (ICNIRP) [2]. A significant ozone concentration was observed mainly in the axial effluent gas flow. Ozone concentration strongly decreases with increasing distance from the plasma source exit nozzle. Conclusion: The investigated APJ exhibits physical properties that might not constitute health risks to humans, e.g. during treatment in dentistry. Thus, the APJ shows a high potential for application as a device in dental therapy.
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    Femtosecond laser induced step-like structures inside transparent hydrogel due to laser induced threshold reduction
    (San Francisco, California, US : PLOS, 2019) Saerchen, Emanuel; Liedtke-Gruener, Susann; Kopp, Maximilian; Heisterkamp, Alexander; Lubatschowski, Holger; Ripken, Tammo
    In the area of laser material processing, versatile applications for cutting glasses and transparent polymers exist. However, parasitic effects such as the creation of step-like structures appear when laser cutting inside a transparent material. To date, these structures were only described empirically. This work establishes the physical and chemical mechanisms behind the observed effects and describes the influence of process and material parameters onto the creation of step-like structures in hydrogel, Dihydroxyethylmethacrylat (HEMA). By focusing laser pulses in HEMA, reduced pulse separation distance below 50 nm and rise in pulse energy enhances the creation of unintended step-like structures. Spatial resolved Raman-spectroscopy was used to measure the laser induced chemical modification, which results into a reduced breakdown threshold. The reduction in threshold influences the position of optical breakdown for the succeeding laser pulses and consequently leads to the step-like structures. Additionally, the experimental findings were supplemented with numerical simulations of the influence of reduced damage threshold onto the position of optical breakdown.
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    Side effects by oral application of atmospheric pressure plasma on the mucosa in mice
    (San Francisco, California, US : PLOS, 2019) Jablonowski, Lukasz; Kocher, Thomas; Schindler, Axel; Müller, Karolina; Dombrowski, Frank; von Woedtke, Thomas; Arnold, Thomas; Lehmann, Antje; Rupf, Stefan; Evert, Matthias; Evert, Katja
    Cold atmospheric pressure plasma (CAP) has been investigated with promising results for peri-implant diseases treatment. However, prior to in-vivo applications of CAP sources in humans, short-term harmful mucosal damage or other unwanted side effects have to be reviewed. 180 male mice (B6C3F1) were divided into twelve treatment groups (n = 15). The right buccal cheek mucosa was treated with CAP. The first and second group each received continuous 10 sec irradiation with 2 different plasma sources (kINPen09, PS-MWM). The third group was treated with the kINPen09 for one minute. Control groups were treated with a corresponding dose of ultraviolet light for 8 seconds or 48 seconds and the other one was left untreated. The animals were weighed before and after treatment. The animals were sacrificed one day or one week after exposure. Stained tissue samples were histologically examined for tissue damage independently by two experienced pathologists. One day after CAP treatment histological analysis showed focal mucosal erosion with superficial ulceration and necrosis accompanied by a mild inflammatory reaction. One week after CAP treatment, the mucosal defects were completely re-epithelialized, associated with remnants of granulation tissue in the stroma irrespective of treatment duration. Furthermore, no cytological atypia was found and no severe weight loss occurred. The control groups did not show any alterations at all. CAP treatment led to a superficial mucosal damage that healed within few days. Nonetheless, further long-term experiments are necessary to exclude undesirable side effects after longer observation time. Particularly, potential carcinogenic effects must be ruled out prior to the application of CAP treatment in daily dental practice.