Summary: Low temperature, high pressure, non-equilibrium plasmas are now routinely used in several material processing applications, and in some cases are competing with low pressure plasmas in areas where these have historically been dominant. Etching and deposition are examples of such applications. Amongst the novel applications of non-equilibrium plasmas, biomedical applications such as electrosurgery, surface modification of biocompatible materials, and the sterilization of heat-sensitive medical tools are particularly interesting. In this paper, first a brief overview of recent research on reduced-pressure plasma-based sterilization/decontamination methods is given. Then a detailed review and discussion on the effects of atmospheric pressure non-equilibrium plasmas on the cells of bacteria is presented. This includes the evaluation of the inactivation kinetics and the roles of the various plasma agents in the inactivation process. Measurements of the plasma temperature, the UV emission, and concentrations of various reactive species for the case of air plasma are presented. Plasma sub-lethal effects are also briefly discussed, and the prospects of the use of “cold” plasmas in the biomedical field are outlined.

Low Temperature Plasma-Based Sterilization: Overview and State-of-the-Art

Can low-temperature plasma technology play a role in medicine? This is a question that many investigators today are trying hard to give a positive answer to. It did not quite start out this way. Almost two decades ago, few ldquocuriousrdquo electrical engineers and physicists with the help of few ldquobraverdquo biologists/microbiologists asked themselves more basic questions: What happens to biological cells if they were exposed to low-temperature plasma? Will they die? Will they survive? If they survive, will they come out the same or somehow ldquoinjuredrdquo? If injured, will they be able to repair the damage and recover? What kind of damage? Which plasma agent causes the damage? etc. As will be shown in this paper, some of these fundamental questions have been partially or fully answered, but until today, a complete picture has yet to emerge. This is good and not so good. It is good because if we already knew all the answers, we would not be looking forward to a more exciting research. It is not so good because after all these years, we are still quite a ways from an implementable medical application. In this review paper, the present state of knowledge regarding the effects of cold plasma on bacteria cells (prokaryotes) and on eukaryotic cells (such as mammalian cells) will be presented. As medical applications where low-temperature plasma is showing signs of success, blood coagulation and wound healing will be described.

/pdf/low-temperature-plasmas-for-medicine-53l81xl7f9.pdf

Low-Temperature Plasmas for Medicine?

In the past cold plasma is used for sterilization of sensitive materials and now it is extended to food industries as a novel technology. For years cold plasma processing has been viewed as useful for microbial inactivation while maintaining quality of fresh produce. However, this process is not effective for in vitro model food systems for inactivation of microbes or enzymes which are present in intact tissues, as it is a surface phenomenon. Cold plasma technology is also used to inactivate endogenous enzymes which are responsible for browning reactions particularly polyphenoloxidase and peroxidases. Several research investigations showed a reduced growth of microorganism via different mode of actions by etching phenomenon, cell disruption by electrophoration etc. Plasma technology is considered as modern non conventional technique which is used for the preparation of modified starches, altering its physical and chemical properties. Overall application of cold plasma for microbial destruction on different food substrates like fruits, meat products, cheese etc. was discussed. Besides this, it is also used to alter the germination rate of seeds. It is an eco-friendly process which is used in the preservation of food and other potential applications as an alternative to common techniques.

/pdf/cold-plasma-a-novel-non-thermal-technology-for-food-5f5ctg3lfl.pdf

Cold Plasma: A novel Non-Thermal Technology for Food Processing

Biological decontamination using a nonthermal gas discharge at atmospheric pressure in air is the subject of significant research effort at this time. The mechanism for bacterial deactivation undergoes a lot of speculation, particularly with regard to the role of ions and reactive gas species. Two mechanisms have been proposed: electrostatic disruption of cell membranes and lethal oxidation of membrane or cytoplasmic components. Results show that death is accompanied by cell lysis and fragmentation in Gram-negative bacteria but not Gram-positive species, although cytoplasmic leakage is generally observed. Gas discharges can be a source of charged particles, ions, reactive gas species, radicals, and radiation (ultraviolet, infrared, and visible), many of which have documented biocidal properties. The individual roles played by these in decontamination are not well understood or quantified. However, the reactions of some species with biomolecules are documented otherwise in the literature. Oxidative stress is relatively well studied, and it is likely that exposure to gas discharges in air causes extreme oxidative challenge. In this paper, a review is presented of the major reactive species generated by nonthermal plasma at atmospheric pressure and the known reactions of these with biological molecules. Understanding these mechanisms becomes increasingly important as plasma-based decontamination and sterilization devices come closer to a wide-scale application in medical, healthcare, food processing, and air purification applications. Approaches are proposed to elucidate the relative importance of reactive species

Bactericidal Action of the Reactive Species Produced by Gas-Discharge Nonthermal Plasma at Atmospheric Pressure: A Review

This paper presents a detailed study of the potential physical mechanisms of the microbial inactivation by cold atmospheric plasmas. With the Bacillus subtilis spores as a model microorganism and an atmospheric-plasma plume in helium flow, optical emission spectroscopy and inactivation kinetics are used to demonstrate the dominating role played by the reactive oxygen species (e.g., atomic oxygen and OH) as well as the minor contributions of the UV photons, heat, charged particles, and electric fields. To differentiate the concentrations of the reactive oxygen species, an atmospheric helium-oxygen plasma is also used for the spore inactivation. Results with the helium and the helium-oxygen plasmas are contrasted to highlight how the production of the spore-killing oxygen species may be enhanced

/pdf/physical-mechanisms-of-inactivation-of-bacillus-subtilis-1q0tbp228o.pdf

Physical Mechanisms of Inactivation of Bacillus subtilis Spores Using Cold Atmospheric Plasmas

In the reduced-pressure (/spl les/10 torr) afterglow stemming from discharges in O/sub 2/- containing mixtures such as N/sub 2/-O/sub 2/, the test-reference spores are ultimately inactivated by UV photons through destruction of their genetic material (DNA). To show this, we assume the inactivation to result from a sufficiently large number of successful hits of the DNA strands by UV photons. This implies that the higher the UV intensity, the shorter the time required to reach the lethal dose. Simultaneously, the increased erosion of the spores by the oxygen atoms as time elapses reduces the incident number of photons required to meet the lethal dose. Erosion, as observed by scanning electron microscopy, also increases with the O/sub 2/ percentage in the mixture. Actually, sterilization time is found to be the shortest when the O/sub 2/ percentage in the mixture is set to maximize the UV emission intensity, which occurs at O/sub 2/ percentages typically below 2%, where erosion is low. This proves the predominant role of UV radiation over erosion as far as spore inactivation is concerned. In any case, plasma sterilization always implies some erosion of the test spores, in contrast to what happens with conventional sterilization methods.

The respective roles of UV photons and oxygen atoms in plasma sterilization at reduced gas pressure: the case of N/sub 2/-O/sub 2/ mixtures

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The respective roles of UV photons and oxygen atoms in plasma sterilization at reduced gas pressure: the case of N/sub 2/-O/sub 2/ mixtures