T. von Woedtke

Antimicrobial treatment of heat sensitive products by miniaturized atmospheric pressure plasma jets (APPJs)

The technological potential of non-thermal plasmas for the antimicrobial treatment of heat sensitive materials is well known. Despite a multitude of scientific activities with considerable progress within the last few years, the realization of industrial plasma-based decontamination or sterilization technology remains a great challenge. This may be due to the fact that an antimicrobial treatment process needs to consider all properties of the product to be treated as well as the requirements of the complete procedure, e.g. a reprocessing cycle of medical instruments. The aim of this work is to demonstrate the applicability of plasma-based processes for the antimicrobial treatment on selected heat sensitive products. The strategy is to use modular, selective and miniaturized plasma sources, which are driven at atmospheric pressure and adaptable to the products to be treated.

Plasma–liquid interactions: a review and roadmap

Plasma–liquid interactions represent a growing interdisciplinary area of research involving plasma science, fluid dynamics, heat and mass transfer, photolysis, multiphase chemistry and aerosol science. This review provides an assessment of the state-of-the-art of this multidisciplinary area and identifies the key research challenges. The developments in diagnostics, modeling and further extensions of cross section and reaction rate databases that are necessary to address these challenges are discussed. The review focusses on non-equilibrium plasmas.

Skin decontamination by low-temperature atmospheric pressure plasma jet and dielectric barrier discharge plasma

BACKGROUND Over the past few years, plasma medicine has become an important field in medical science. Cold plasma has proven anti-inflammatory, antimicrobial and antineoplastic effects. AIM To test the decontamination power of two cold plasma sources [low-temperature atmospheric pressure plasma jet (APPJ) and dielectric barrier discharge plasma (DBD)] in vivo on human fingertips. METHODS After 3, 15, 30, 60, 90, 120, 150, 180, 210 and 240 s of spot treatment with the APPJ and DBD, the log reduction factors (RFs) of physiological (PF) and artificially (AF) contaminated flora (Staphylococcus epidermidis and Micrococcus luteus) were calculated. The bacterial load was determined after counting. Tolerance (paresthesia, pain and heat) was measured using a numerical rating scale. FINDINGS Both plasma devices led to a significant reduction in PF and AF. The maximum log reduction factors for PF were 1.3 for the DBD at 210 s and 0.8 for the APPJ at 60 s. For AF, the maximum log reduction factors were 1.7 for the DBD at 90 s and 1.4 for the APPJ at 120 s. Treatment with both devices was well tolerated. CONCLUSION Both the APPJ and DBD were highly effective in eradicating PF and AF from the fingertips of healthy volunteers. No plasma-resistant isolates were observed. Cold plasma appears to have potential for skin disinfection. For hand hygiene purposes, plasma exposure times would need to be reduced significantly by technical means.

In Vitro Killing of Clinical Fungal Strains by Low-Temperature Atmospheric-Pressure Plasma Jet

Plasma medicine is an expanding focus and offers new aspects of therapy combining potent physical partial efficacies, like such as ultraviolet, infrared, and reactive species and particles, and nowadays, many successful treatments of different illnesses have been described. Fungal skin and nail infections pose significant therapeutic and economical problems. To test the plasma susceptibility of clinical strains of the most frequently encountered fungal species involved in dermatomycosis, clinical isolates of Trichophyton interdigitale, Trichophyton rubrum, Microsporum canis, and Candida albicans were irradiated by a cold atmospheric pressure plasma jet. Punctual plasma irradiation eradicated fungal growth of all species with the largest inactivation zones with most progress in the first 15 s of treatment, treating C. albicans and least progress in that of , the lowest being M. canis. No isolate exhibited resistance to plasma treatment. Plasma treatment also completely eradicated reproductive fungal elements of T. interdigitale in dandruff of patients with tinea pedis ex vivo and in the environment in contaminated shoes. Accordingly, cold plasma seems suited to antifungal in vivo treatment of fungal skin infections and decontamination of environmental infective material.

Antimicrobial Effects of UV and VUV Radiation of Nonthermal Plasma Jets

Radio-frequency-driven plasma jets in argon at atmospheric pressure have been shown to emit a significant amount of UV and VUV radiation. There is an increasing interest in the use of UV and VUV photons in many fields of research and in industry, in particular for life-science applications. In order to study the antimicrobial effect of plasma-emitted UV and VUV radiation, microbiological tests and plasma diagnostics are combined. In particular, quantitative values of irradiance are estimated. The VUV emission of the plasma jet is dominated by the emission of argon excimer (Ar2). The recorded spectra between 115 and 180 nm also include several atomic emission lines of nitrogen and oxygen. The UV emissions are due to molecular bands of NO, OH, and N2. The best antimicrobial effect is observed by means of direct plasma treatment. UV and VUV emissions have a lower effect, and there is no difference observed between these two components.

Risk assessment of a cold argon plasma jet in respect to its mutagenicity

Cold atmospheric pressure plasmas represent a favorable option for the treatment of heat sensitive materials and human or animal tissue. Beneficial effects have been documented in a variety of medical conditions, e.g., in the treatment of chronic wounds. It is assumed that the main mechanism of the plasmas efficacy is mediated by a stimulating dissipation of energy via radiation and/or chemical energy. Although no evidence on undesired side effects of a plasma treatment has yet been presented, skepticism toward the safety of the exposure to plasma is present. However, only little data regarding the mutagenic potential of this new treatment option is available. Accordingly, we investigated the mutagenic potential of an argon plasma jet (kinpen) using different testing systems in accordance with ISO norms and multiple cell lines: a HPRT1 mutation assay, a micronucleus formation assay, and a colony formation assay. Moderate plasma treatment up to 180 s did not increase genotoxicity in any assay or cell type investigated. We conclude that treatment with the argon plasma jet kinpen did not display a mutagenic potential under the test conditions applied and may from this perspective be regarded as safe for the use in biomedical applications.

Induction of proliferation of basal epidermal keratinocytes by cold atmospheric-pressure plasma.

Over the past few decades, new cold plasma sources have been developed that have the great advantage of operating at atmospheric pressure and at temperatures tolerable by biological material. New applications for these have emerged, especially in the field of dermatology. Recently it was demonstrated that cold atmospheric‐pressure plasma positively influences healing of chronic wounds. The potential of cold plasma lies in its capacity to reduce bacterial load in the wound while at the same time stimulating skin cells and therefore promoting wound closure. In recent years, there have been great advances in the understanding of the molecular mechanisms triggered by cold plasma involving signalling pathways and gene regulation in cell culture.

Investigation of Surface Etching of Poly(Ether Ether Ketone) by Atmospheric-Pressure Plasmas

An atmospheric-pressure argon plasma jet with varying admixtures of molecular oxygen was used to study the etching mechanism of poly(ether ether ketone) (PEEK). Furthermore, a correlation between plasma-based etching processes on PEEK with the generation of chemically reactive plasma species is proposed. The surface analysis was performed by X-ray photoelectron spectroscopy, atomic force microscopy, and surface profilometry which showed a dramatic increase in the content of oxygen functionalities and surface roughness after long-time Ar/O2-plasma treatment. For the plasma diagnostics, two-photon absorption laser-induced fluorescence spectroscopy was applied. The obtained etching mass as well as the surface roughness for different molecular oxygen admixtures revealed a strong dependence on the atomic-oxygen density. Furthermore, the radial surface profile, affected by plasma etching, might be attributed to the distribution of plasma-generated oxygen species in the plasma jet effluent.

Campus PlasmaMed—From Basic Research to Clinical Proof

Plasma medicine is emerging worldwide, and some promising applications seem to be near the horizon. Direct therapeutic plasma application as the central field of plasma medicine will bring physical plasmas directly on or in a human (or animal) body. Campus PlasmaMed is a research association supported by the German Federal Ministry of Education and Research (BMBF), concentrated in the northeast of Germany and founded to explore promising and safe applications of atmospheric-pressure plasmas in medical therapy based on systematic and interdisciplinary basic research on the interactions of plasma components with living systems. Whereas a broad spectrum of plasma sources dedicated for biomedical applications has been reported during recent years, mainly two basic principles of plasma sources are used in the Campus PlasmaMed: atmospheric-pressure plasma jets and dielectric barrier discharges. A comprehensive assessment of potential risk factors, such as gas temperature, power transfer from plasma to the target, (V)UV radiation emission, or the generation of toxic gases and its release into the adjacencies, which could be dangerous for patients and therapists, has to be done as a basic precondition before any biomedical experiments can be started or a potential therapeutic application can be taken into consideration. Despite the fact that the initial plasma-source characterization and optimization are in the main responsibility of plasma physicists and engineers, potential users from the biomedical field should be integrated as soon as possible to include special needs and constraints for specific applications during early steps of development. This multidisciplinary research cooperation among plasma scientists and engineers on the one side and life scientists and clinicians on the other is one of the main characteristics of the Campus PlasmaMed. Such interdisciplinary cooperation is more than ever required for the characterization of biological effects of plasma sources, which has to be realized by a multistep program, starting with the investigations of plasma-liquid interactions and including a broad spectrum of in vitro tests with cells, as well as cell and tissue cultures up to isolated tissues or organs to be proved finally with animal experiments and clinical trials. Because there are no standardized criteria so far according to which atmospheric-pressure plasma sources can be assessed as to their suitability for medical applications, interdisciplinary results from plasma medical research have to be transferred into rules and standards to guarantee successful and safe practical application, including economic exploitation of plasma-medical research results.

New Nonthermal Atmospheric-Pressure Plasma Sources for Decontamination of Human Extremities

The research and development of plasma sources, which can be used for therapeutic applications in the new and emerging field of plasma medicine, has gained more and more interest during recent years. These applications require cold nonthermal plasmas operating at atmospheric pressure. Due to the fact that, in general, plasma on or in the human body is a challenge both for medicine and plasma physics, basic research combining experimental physical and biological investigation and modeling is necessary to provide the required knowledge for therapeutic applications. It turned out that each application needs a special tailor-made plasma source, passing a minimum set of physical and biological tests before it can be considered for medical use. In addition to atmospheric-pressure plasma jets, dielectric barrier discharges offer great potential for a variety of medical indications. A new 2-D and even 3-D acting plasma source is introduced, exemplified for a possible decontamination of human extremities or similar tasks. In contradiction to most of todays existing plasma sources with fixed electrodes and nozzles, the prototype uses flexible electrodes to automatically adapt the plasma under equal and stable conditions to nearly all surface structures. First, physical and biological investigations demonstrate the general potential for therapeutic applications on preferably intact skin surfaces.