This introductory review on plasma health care is intended to provide the interested reader with a summary of the current status of this emerging field, its scope, and its broad interdisciplinary approach, ranging from plasma physics, chemistry and technology, to microbiology, biochemistry, biophysics, medicine and hygiene. Apart from the basic plasma processes and the restrictions and requirements set by international health standards, the review focuses on plasma interaction with prokaryotic cells (bacteria), eukaryotic cells (mammalian cells), cell membranes, DNA etc. In so doing, some of the unfamiliar terminology—an unavoidable by-product of interdisciplinary research—is covered and explained. Plasma health care may provide a fast and efficient new path for effective hospital (and other public buildings) hygiene— helping to prevent and contain diseases that are continuously gaining ground as resistance of pathogens to antibiotics grows. The delivery of medically active 'substances' at the molecular or ionic level is another exciting topic of research through effects on cell walls (permeabilization), cell excitation (paracrine action) and the introduction of reactive species into cell cytoplasm. Electric fields, charging of surfaces, current flows etc can also affect tissue in a controlled way. The field is young and hopes are high. It is fitting to cover the beginnings in New Journal of Physics, since it is the physics (and non- equilibrium chemistry) of room temperature atmospheric pressure plasmas that have made this development of plasma health care possible.

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Plasma medicine: an introductory review

Nonthermal plasma (NTP) is electrically energized matter and is composed of highly reactive species including gas molecules, charged particles in the form of positive ions, negative ions, free radicals, electrons and quanta of electromagnetic radiation (photons) at near-room temperature. NTP technology is an emerging nonthermal technology with potential applications for sterilization in the food industries. An upsurge in the research activities for plasma-based inactivation of food-borne pathogens is evident in recent years. These studies have shown that NTP can be used for the surface decontamination of raw produce including; dried nuts and packaging materials. This paper reviews the action of plasma agents on the microbial classes and describes proven and potential applications in food processing. Novel developments in the technology and a future outlook for the application to foods are discussed.

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Nonthermal Plasma Inactivation of Food-Borne Pathogens

Cold plasma technology is an emerging, green process offering many potential applications for food packaging. While it was originally developed to increase the surface energy of polymers, enhancing adhesion and printability, it has recently emerged as a powerful tool for surface decontamination of both foodstuffs and food packaging materials. New trends aim to develop in-package decontamination, offering non-thermal treatment of foods post-packaging. This paper provides an overview of cold plasma theory, equipment and summarises recent advances in the modification of polymeric food packaging materials along with potential applications in the food industry.

Applications of cold plasma technology in food packaging

The recent tremendous progress in understanding physical plasma phenomenon, together with the development of new plasma sources has put growing focus on the application of plasmas in health care. Active plasma components, such as molecules, atoms, ions, electrons and photons, reactive species, ultraviolet radiation, optical and infrared emission and heat have the ability of activating, controlling and catalysing reactions and complex biochemical procedures. Thermal and non-thermal (i.e. cold) plasmas - both already widely established in medicine - are used for various therapeutic applications. Particularly in dermatology, plasma applications hold big potential, for example, in wound healing, such as efficient disinfection or sterilization, therapy of various skin infections or tissue regeneration. This review gives an overview on potential plasma applications in medicine - including the recent research on skin diseases - and summarizes possible interactions between plasmas and living tissue.

Plasma applications in medicine with a special focus on dermatology

A distributed antenna system is provided that frequency shifts the output of one or more microcells to a 60 GHz or higher frequency range for transmission to a set of distributed antennas. The cellular band outputs of these microcell base station devices are used to modulate a 60 GHz (or higher) carrier wave, yielding a group of subcarriers on the 60 GHz carrier wave. This group will then be transmitted in the air via analog microwave RF unit, after which it can be repeated or radiated to the surrounding area. The repeaters amplify the signal and resend it on the air again toward the next repeater. In places where a microcell is required, the 60 GHz signal is shifted in frequency back to its original frequency (e.g., the 1.9 GHz cellular band) and radiated locally to nearby mobile devices.

Remote distributed antenna system

A microwave driven low pressure plasma reactor is developed based on a modiﬁed Plasmaline antenna for plasma processing of polyethylene terephthalate (PET) foils and bottles. It allows for the treatment of thermolabile packaging materials, e.g. plasma sterilization and permeation barrier coating. Silicon oxide ﬁlms are deposited on PET foils as a permeation barrier coating. A pulsed hexamethyldisiloxane:oxygen plasma is ignited under various conditions and the oxygen permeation is investigated. A criterion for the homogeneous deposition of SiO x coatings is described depending on the residence time of process gases. Additionally, the composition of the coatings is analyzed by means of Fourier transform infrared spectroscopy regarding carbon and hydrogen content. A strong relation between barrier properties and ﬁlm composition is found: good oxygen barriers are observed as carbon content is reduced and ﬁlms become inorganic, quartz-like. A residual permeation as low as J  = 1.0 ± 0.3 cm 3 m − 2 day − 1 bar − 1 for SiO x coated PET foils is achieved. The dependencies of important plasma parameters, such as gas mixture, process pressure, power and pulse conditions on oxygen permeation through packaging foil are shown to optimize the coating process.

Pulsed microwave plasma polymerization of silicon oxide ﬁlms: Application of efficient permeation barriers on polyethylene terephthalate

Low-Pressure Microwave Plasma Sterilization of Polyethylene Terephthalate Bottles

Silicon oxide barrier layers are deposited on polyethylene terephthalate as permeation barriers for food packaging applications by means of a low pressure microwave plasma. Hexamethyldisiloxane (HMDSO) and oxygen are used as process gases to deposit SiOx coatings via pulsed low pressure plasmas. The layer composition of the coating is investigated by Fourier transform infrared spectroscopy and energy dispersive x-ray spectroscopy to show correlations with barrier properties of the films. The oxygen permeation barrier is determined by the carrier gas method using an electrochemical detector. The transition from low to high barrier films is mapped by the transition from organic SiOxCyHz layers to quartz-like SiO1.7 films containing silanol bound hydrogen. A residual permeation as low as J = 1 ± 0.3 cm3 m−2 day−1 bar−1 is achieved, which is a good value for food packaging applications. Additionally, the activation energy Ep of oxygen permeation is analysed and a strong increase from Ep = 31.5 kJ mol−1 for SiOx CyHz-like coatings to Ep = 53.7 kJ mol−1 for SiO1.7 films is observed by increasing the oxygen dilution of HMDSO:O2 plasma. The reason for the residual permeation of high barrier films is discussed and coating defects are visualized by capacitively coupled atomic oxygen plasma etching of coated substrates. A defect density of 3000 mm−2 is revealed.

http://iopscience.iop.org/article/10.1088/0022-3727/41/13/135207/pdf

Permeation mechanisms of pulsed microwave plasma deposited silicon oxide films for food packaging applications

The results of silicon oxide permeation barrier coating and plasma sterilization are shown using a low-pressure microwave plasma reactor system based on a Plasmaline antenna developed for the treatment of polyethylene terephthalate bottles and foils. The influence of the coating composition on the barrier properties is analyzed and a good correlation is found. The optimized barrier coatings are analyzed regarding coating defects, which are visualized by means of capacitively coupled oxygen plasma etching of the coated substrates. The capabilities of plasma sterilization are exemplarily demonstrated for spores of Bacillus atrophaeus allowing for a spore reduction according to today's regulations for aseptic food packaging.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/ppap.200930907

Silicon Oxide Permeation Barrier Coating and Plasma Sterilization of PET Bottles and Foils

There is a growing demand for bottles made of polyethylene terephthalate (PET) on the global market. However, PET offers poor barrier properties against gas permeation and the shelf live of packaged food is reduced. A permeation barrier coating of PET bottles and foils is developed by means of a microwave driven low pressure plasma reactor based on a modified Plasmaline antenna. Barrier performance is enhanced by depositing a transparent plasma polymerized silicon oxide (SiO x ) coating on the inner surface of the PET bottle [1]. Up to now SiO x -barrier coatings on foils and hollow bodies are deposited and characterised without control of the ion energy. The influence of ion energy on the characteristics of plasma and coating is investigated using a substrate bias to generate variable ion energy distributions. Barrier properties are determined concerning oxygen and carbon dioxide permeation. The composition of the coatings regarding carbon and hydrogen content is analyzed by means of Fourier transform infrared spectroscopy (FTIR). A strong relation between barrier properties and film composition is found: good oxygen barriers are observed as carbon content is reduced and films become quartz like. Atomic oxygen etching of the coated substrate visualizes coating defects responsible for a residual permeation [2]. Absolut calibrated optical emission spectroscopy and Langmuir probe measurements yield in plasma parameter, such as electron density (n e ), average electron energy (E mean

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Michael Deilmann

Papers

Pulsed microwave plasma polymerization of silicon oxide ﬁlms: Application of efficient permeation barriers on polyethylene terephthalate

Low-Pressure Microwave Plasma Sterilization of Polyethylene Terephthalate Bottles

Permeation mechanisms of pulsed microwave plasma deposited silicon oxide films for food packaging applications

Silicon Oxide Permeation Barrier Coating and Plasma Sterilization of PET Bottles and Foils

Silicon oxide permeation barrier coating of PET bottles and foils