Manfred Stieber

Atmospheric-pressure plasma sources: Prospective tools for plasma medicine

Plasma-based treatment of chronic wounds or skin diseases as well as tissue engineering or tumor treatment is an extremely promising field. First practical studies are promising, and plasma medicine as an independent medical field is emerging worldwide. While during the last years the basics of sterilizing effects of plasmas were well studied, concepts of tailor-made plasma sources which meet the technical requirements of medical instrumentation are still less developed. Indeed, studies on the verification of selective antiseptic effects of plasmas are required, but the development of advanced plasma sources for biomedical applications and a profound knowledge of their physics, chemistry, and parameters must be contributed by physical research. Considering atmospheric-pressure plasma sources, the determination of discharge development and plasma parameters is a great challenge, due to the high complexity and limited diagnostic approaches. This contribution gives an overview on plasma sources for therapeutic applications in plasma medicine. Selected specific plasma sources that are used for the investigation of various biological effects are presented and discussed. Furthermore, the needs, prospects, and approaches for its characterization from the fundamental plasma physical point of view will be discussed.

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.

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.

Sterilization of enzyme glucose sensors: problems and concepts.

A useful method of enzyme glucose sensor sterilization has not only to ensure the needs of sterility assurance but has also to guarantee the functional stability of the sensors. The action of 2 or 3% alkalinized glutaraldehyde solution, as well as gamma irradiation with a dose of 25 kGy caused changes of the in vitro functionality and polymer material irritations, respectively. After a combined treatment by 0.6% hydrogen peroxide solution acting over 4 days with 7 kGy gamma irradiation only a slight loss of sensitivity must be registered. The combination of a specially designed universal homogeneous ultraviolet irradiation over 300 s with a 3 days lasting treatment by an inclusion compound of hydrogen peroxide with tensides in urea (0.15% effective hydrogen peroxide concentration) did not cause any influence on the glucose sensor function in vitro. With all methods tested here, a Bacillus subtilis spore reduction over 8 log(10) cycles from 10(6) to 10(-2) spores per test object on an average could be proved experimentally. In general, if non-thermal methods must be used it seems to be impossible to guarantee a sterility assurance level of 10(-6) as it is demanded by the pharmacopoeias. Consequently, effective concepts to produce sterile glucose biosensors for medical and biological applications should be based not only on final product treatments but should include germ reducing measures in every manufacturing step.

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.

Plasma decontamination at atmospheric pressure - basics and applications

Plasma sources, driven at atmospheric pressure gain more and more interest due to the technological advantages (avoidance of vacuum devices and batch processing). Especially nonthermal plasmas at atmospheric pressure for the antimicrobial treatment of heat sensitive materials are of rapidly growing interest. However, the realisation of industrial plasma-based decontamination or sterilisation technology remains a great challenge. This is 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 process and all boundary conditions. First the requirements for plasma-decontamination and plasma-sterilization will be discussed. Advantages and disadvantages regarding present no-plasma decontamination processes will be indicated. The applicability of plasma-based processes for the antimicrobial treatment on selected, heat sensitive products will be demonstrated. Modular and selective plasma sources will be used to match the specific requirements regarding decontamination of medical products. Nearly any complex 3-dimensional structure can be treated by the plasma sources developed. In particular catheters for intracardial electrophysiological studies as well as the antimicrobial treatment process of hollow packaging for pharmaceutical products, namely PET- bottles, will be discussed. Furthermore the contribution will report on attempts and difficulties concerning the adaptation of the plasma sources on such real products. Optical emission spectroscopy of the plasma sources and micro-biological tests will complete the investigation.

Antimicrobial Treatment of Heat Sensitive Products by Atmospheric Pressure Plasma Sources

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 years the realization of industrial plasma-based decontamination or sterilization technology remains a great challenge. The aim of the work presented in this contribution is to demonstrate the applicability of plasma-based processes for the antimicrobial treatment on selected, heat sensitive products. The idea is to use modular and selective plasma sources. These plasma sources are driven at atmospheric pressure due to its technological advantages (avoidance of vacuum devices and batch processing). According to the specific requirements given by the product different plasma sources, namely rf-driven plasma jets, microwave-driven air plasmas are used.