From patent to product? 50 years of low-pressure plasma sterilization

The development of new sterilization methods is still a major topic. The need for new techniques arises from the development of new instruments and the usage of different materials. Especially in the case of plastics with their beneficial properties, for example, in the field of implantology, plasma sterilization is seen as a promising alternative to the standard methods. However, 50 years after the first patent and although low-pressure plasmas show excellent inactivation performance (>log 6 reduction), only one commercial system is available on the market for a distinct application. We will give a short review about known plasma sterilization mechanisms, the different plasma sterilization systems in use, analyze possible challenges for an industrial process and comment on possible solutions for a broader acceptance and utilization of low-pressure plasma sterilization

Elucidation of Plasma-induced Chemical Modifications on Glutathione and Glutathione Disulphide

Cold atmospheric pressure plasmas are gaining increased interest in the medical sector and clinical trials to treat skin diseases are underway. Plasmas are capable of producing several reactive oxygen and nitrogen species (RONS). However, there are open questions how plasma-generated RONS interact on a molecular level in a biological environment, e.g. cells or cell components. The redox pair glutathione (GSH) and glutathione disulphide (GSSG) forms the most important redox buffer in organisms responsible for detoxification of intracellular reactive species. We apply Raman spectroscopy, mass spectrometry, and molecular dynamics simulations to identify the time-dependent chemical modifications on GSH and GSSG that are caused by dielectric barrier discharge under ambient conditions. We find GSSG, S-oxidised glutathione species, and S-nitrosoglutathione as oxidation products with the latter two being the final products, while glutathione sulphenic acid, glutathione sulphinic acid, and GSSG are rather reaction intermediates. Experiments using stabilized pH conditions revealed the same main oxidation products as were found in unbuffered solution, indicating that the dominant oxidative or nitrosative reactions are not influenced by acidic pH. For more complex systems these results indicate that too long treatment times can cause difficult-to-handle modifications to the cellular redox buffer which can impair proper cellular function

GSH modification as a marker for plasma source and biological response comparison to plasma treatment

This study investigated the use of glutathione as a marker to establish a correlation between plasma parameters and the resultant liquid chemistry from two distinct sources to predefined biological outcomes. Two different plasma sources were operated at parameters that resulted in similar biological responses: cell viability, mitochondrial activity, and the cell surface display of calreticulin. Specific glutathione modifications appeared to be associated with biological responses elicited by plasma. These modifications were more pronounced with increased treatment time for the European Cooperation in Science and Technology Reference Microplasma Jet (COST-Jet) and increased frequency for the dielectric barrier discharge and were correlated with more potent biological responses. No correlations were found when cells or glutathione were exposed to exogenously added long-lived species alone. This implied that short-lived species and other plasma components were required for the induction of cellular responses, as well as glutathione modifications. These results showed that comparisons of medical plasma sources could not rely on measurements of long-lived chemical species; rather, modifications of biomolecules (such as glutathione) might be better predictors of cellular responses to plasma exposure. © 2020 by the authors

Nitrosylation vs. oxidation – How to modulate cold physical plasmas for biological applications

Thiol moieties are major targets for cold plasma-derived nitrogen and oxygen species, making CAPs convenient tools to modulate redox-signaling pathways in cells and tissues. The underlying biochemical pathways are currently under investigation but especially the role of CAP derived RNS is barely understood. Their potential role in protein thiol nitrosylation would be relevant in inflammatory processes such as wound healing and improving their specific production by CAP would allow for enhanced treatment options beyond the current application. The impact of a modified kINPen 09 argon plasma jet with nitrogen shielding on cysteine as a thiol-carrying model substance was investigated by FTIR spectroscopy and high-resolution mass spectrometry. The deposition of short-lived radical species was measured by electron paramagnetic resonance spectroscopy, long-lived species were quantified by ion chromatography (NO2-, NO3-) and xylenol orange assay (H2O2). Product profiles were compared to samples treated with the so-called COST jet, being introduced by a European COST initiative as a reference device, using both reference conditions as well as conditions adjusted to kINPen gas mixtures. While thiol oxidation was dominant under all tested conditions, an Ar + N2/O2 gas compositions combined with a nitrogen curtain fostered nitric oxide deposition and the desired generation of S-nitrosocysteine. Interestingly, the COST-jet revealed significant differences in its chemical properties in comparison to the kINPen by showing a more stable production of RNS with different gas admixtures, indicating a different •NO production pathway. Taken together, results indicate various chemical properties of kINPen and COST-jet as well as highlight the potential of plasma tuning not only by gas admixtures alone but by adjusting the surrounding atmosphere as well

Foundations of plasma standards

The field of low-temperature plasmas (LTPs) excels by virtue of its broad intellectual diversity, interdisciplinarity and range of applications. This great diversity also challenges researchers in communicating the outcomes of their investigations, as common practices and expectations for reporting vary widely in the many disciplines that either fall under the LTP umbrella or interact closely with LTP topics. These challenges encompass comparing measurements made in different laboratories, exchanging and sharing computer models, enabling reproducibility in experiments and computations using traceable and transparent methods and data, establishing metrics for reliability, and in translating fundamental findings to practice. In this paper, we address these challenges from the perspective of LTP standards for measurements, diagnostics, computations, reporting and plasma sources. This discussion on standards, or recommended best practices, and in some cases suggestions for standards or best practices, has the goal of improving communication, reproducibility and transparency within the LTP field and fields allied with LTPs. This discussion also acknowledges that standards and best practices, either recommended or at some point enforced, are ultimately a matter of judgment. These standards and recommended practices should not limit innovation nor prevent research breakthroughs from having real-time impact. Ultimately, the goal of our research community is to advance the entire LTP field and the many applications it touches through a shared set of expectations

The role of humidity and UV-C emission in the inactivation of B. subtilis spores during atmospheric-pressure dielectric barrier discharge treatment

Experiments are performed to assess the inactivation of Bacillus subtilis spores using a non-thermal atmospheric-pressure dielectric barrier discharge. The plasma source used in this study is mounted inside a vacuum vessel and operated in controlled gas mixtures. In this context, spore inactivation is measured under varying nitrogen/oxygen and humidity content and compared to spore inactivation using ambient air. Operating the dielectric barrier discharge in a sealed vessel offers the ability to distinguish between possible spore inactivation mechanisms since different process gas mixtures lead to the formation of distinct reactive species. The UV irradiance and the ozone density within the plasma volume are determined applying spectroscopic diagnostics with neither found to fully correlate with spore inactivation. It is found that spore inactivation is most strongly correlated with the humidity content in the feed gas, implying that reactive species formed, either directly or indirectly, from water molecules are strong mediators of spore inactivation

Plasma Control: A Review of Developments and Applications of Plasma Medicine Control Mechanisms

Cold atmospheric plasmas (CAPs) within recent years have shown great promise in the field of plasma medicine, encompassing a variety of treatments from wound healing to the treatment of cancerous tumors. For each subsequent treatment, a different application of CAPs has been postulated and attempted to best treat the target for the most effective results. These treatments have varied through the implementation of control parameters such as applied settings, electrode geometries, gas flow, and the duration of the treatment. However, with such an extensive number of variables to consider, scientists and engineers have sought a means to accurately control CAPs for the best-desired effects in medical applications. This paper seeks to investigate and characterize the historical precedent for the use of plasma control mechanisms within the field of plasma medicine. Current control strategies, plasma parameters, and control schemes will be extrapolated through recent developments and successes to gain better insight into the future of the field and the challenges that are still present in the overall implementation of such devices. Proposed approaches, such as data-driven machine learning, and the use of closed-loop feedback controls, will be showcased as the next steps toward application

Plasma technical and microbiological characterization of newly developed VHF plasmas

Zur Sterilisation medizinischer Instrumente wird ein kapazitiv gekoppeltes Niederdruckplasma (VHF-CCP) entwickelt und mit optischer Emissionsspektroskopie, Multipolresonanzsonde und Langmuir Sonde charakterisiert. Mittels CCD-Kamera und ortsaufgelösten Sondenmessungen wird die Homogenität der Entladung untersucht und ein homogener Bereich für die Sterilisation definiert. Sterilisationsversuche mit Testkeimen bestätigen die Sterilisationsleistung des VHF-CCP. Zur Untersuchung der Sterilisationsmechanismen werden sowohl Plasma als auch Bakterien in Einzelbestandteilen untersucht. Hierfür wird ein alternativer UV+Hitze-Aufbau verwendet, der es ermöglicht UV-Strahlung und Hitze des Plasmas nachzubilden. Bio-Makromoleküle werden ausgewählt, um den Einfluss von Plasma auf einzelne Zellbestandteile zu untersuchen. Hierbei liegt der Fokus auf Proteinen und DNA. Aus den gewonnenen Erkenntnissen wird ein Desktopsterilisator zur Sterilisation medizinischer Instrumente entwickelt.A capacitively coupled low-pressure plasma (VHF-CCP) is developed for the sterilization of medical instruments and characterized by means of optical emission spectroscopy, multipole resonance probe and Langmuir probe diagnostics. Homogeneity of the discharge is investigated with a CCD camera and space-resolved probe measurements. A homogeneous area for sterilization is defined. Sterilization tests confirm sterilization efficacy of the VHF-CCP. In order to unravel sterilization mechanisms, single components of plasma as well as of bacteria are investigated. Therefore, an alternative UV+heat-setup is employed, enabling to re-enact UV radiation and heat of the plasma. Bio-macromolecules are selected to investigate the impact of plasma on single cell components. Here, the focus is on proteins and DNA. From the results obtained, a desktop sterilizer for the sterilization of medical instruments is developed

Advances in Plasma Oncology toward Clinical Translation

This Special Issue on “Advances in Plasma Oncology Toward Clinical Translation” aims to bring together cutting-edge research papers within the field in the context of clinical translation and application [...