Nikita Bibinov

A double inductively coupled plasma for sterilization of medical devices

A double inductively coupled low pressure plasma for sterilization of bio-medical materials is introduced. It is developed for homogeneous treatment of three-dimensional objects. The short treatment times and low temperatures allow the sterilization of heat sensitive materials like ultra-high-molecular-weight-polyethylene or polyvinyl chloride. Using a non-toxic atmosphere reduces the total process time in comparision with common methods. Langmuir probe measurements are presented to show the difference between ICP- and CCP-mode discharges, the spatial homogeneity and the influence on the sterilization efficiency. To know more about the sterilization mechanisms optical emission is measured and correlated with sterilization results.

Characterization of DBD plasma source for biomedical applications

The dielectric barrier discharge (DBD) plasma source for biomedical application is characterized using optical emission spectroscopy, plasma-chemical simulation and voltage–current measurements. This plasma source possesses only one electrode covered by ceramic. Human body or some other object with enough high electric capacitance or connected to ground can serve as the opposite electrode. DBD consists of a number of microdischarge channels distributed in the gas gap between the electrodes and on the surface of the dielectric. To characterize the plasma conditions in the DBD source, an aluminium plate is used as an opposite electrode. Electric parameters, the diameter of microdischarge channel and plasma parameters (electron distribution function and electron density) are determined. The gas temperature is measured in the microdischarge channel and calculated in afterglow phase. The heating of the opposite electrode is studied using probe measurement. The gas and plasma parameters in the microdischarge channel are studied at varied distances between electrodes. According to an energy balance study, the input microdischarge electric energy dissipates mainly in heating of electrodes (about 90%) and partially (about 10%) in the production of chemical active species (atoms and metastable molecules).

Identification of the most efficient VUV/UV radiation for plasma based inactivation of Bacillus atrophaeus spores

The identification of sterilization agents is mandatory to achieve sterilization mechanisms in low-pressure discharges. A detailed account of each agent is required for improvements, development and establishment of plasma sterilization as an alternative to traditional sterilization processes. Sterilization agents are VUV and UV radiation, photodesorption producing volatile species and etching of spore coat and membrane. This work focuses on VUV and UV radiation as a sterilization agent of Bacillus atrophaeus spores. Four wavelength ranges are distinguished: the emission spectra above 300 nm, above 235 nm, above 112 nm and a full emission spectrum including active species. The range from 235 up to 300 nm without active species is identified to be the most capable for sterilizing Bacillus atrophaeus spores.

Biological effects of nitric oxide generated by an atmospheric pressure gas-plasma on human skin cells

Physical plasmas which contain a mixture of different radicals, charged species and UV-radiation, have recently found entry in various medical applications. Though first clinical trials are underway nothing is known about the plasma components mediating the biological effects seen and safety concerns have been neglected. We here use for the first time a plasma device equipped with a bent quartz capillary to omit UV-radiation by directing the gas flux only, containing high concentrations of NO, onto cultured human skin cells. This enables us to compare the effects of plasma produced radical species alone - mainly NO - and in combination with the also emitted UV-radiation on cells. Evaluation of cell death after different treatment times with the capillary present shows no sign of apoptosis in primary human keratinocytes even after 15 min plasma exposure. In human skin endothelial cells however, toxicity is elevated after treatment for more than 10 min. In contrast, without the capillary treatment of both cell types results in maximal cell death after 10 min. Measuring nitrite and nitrosothiols reveals that plasma-treatment leads to an increase of these NO-products in buffer solution and cell culture medium. Using an intracellular fluorescent NO-probe and analysing the nitrosation status of plasma exposed skin cells we can prove that NO indeed reaches and penetrates into these cells. Non-toxic exposure times modulate proliferation in both cell types used, indicating that the gas species, mainly NO, are biological active.

DBD plasma source operated in single-filamentary mode for therapeutic use in dermatology

Our dielectric barrier discharge (DBD) plasma source for bio-medical application comprises a copper electrode covered with ceramic. Objects of high capacitance such as the human body can be used as the opposite electrode. In this study, the DBD source is operated in single-filamentary mode using an aluminium spike as the opposite electrode, to imitate the conditions when the discharge is ignited on a raised point, such as hair, during therapeutic use on the human body. The single-filamentary discharge thus obtained is characterized using optical emission spectroscopy, numerical simulation, voltage–current measurements and microphotography. For characterization of the discharge, averaged plasma parameters such as electron distribution function and electron density are determined. Fluxes of nitric oxide (NO), ozone (O3) and photons reaching the treated surface are simulated. The calculated fluxes are finally compared with corresponding fluxes used in different bio-medical applications.

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

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.

Non-thermal atmospheric pressure HF plasma source: generation of nitric oxide and ozone for bio-medical applications

A new miniature high-frequency (HF) plasma source intended for bio-medical applications is studied using nitrogen/oxygen mixture at atmospheric pressure. This plasma source can be used as an element of a plasma source array for applications in dermatology and surgery. Nitric oxide and ozone which are produced in this plasma source are well-known agents for proliferation of the cells, inhalation therapy for newborn infants, disinfection of wounds and blood ozonation.Using optical emission spectroscopy, microphotography and numerical simulation, the gas temperature in the active plasma region and plasma parameters (electron density and electron distribution function) are determined for varied nitrogen/oxygen flows. The influence of the gas flows on the plasma conditions is studied. Ozone and nitric oxide concentrations in the effluent of the plasma source are measured using absorption spectroscopy and electro-chemical NO-detector at variable gas flows. Correlations between plasma parameters and concentrations of the particles in the effluent of the plasma source are discussed. By varying the gas flows, the HF plasma source can be optimized for nitric oxide or ozone production. Maximum concentrations of 2750 ppm and 400 ppm of NO and O3, correspondingly, are generated.

Direct current plasma jet needle source

Direct current plasma jet source operated in a glow regime is studied by applying nitrogen as a feed gas. This plasma jet generates fluxes of atoms, which are produced in the small region near the cathode tip characterized by high luminosity and a high dissociation rate of molecules. The nitrogen atoms carried away from this region by the feed gas flow form the narrow effluent of the plasma jet source. The gas temperature in the effluent flow is lower than 400 K despite the relatively high temperature of up to 950 K in the active plasma zone near the cathode tip.

Low-pressure microwave plasma sterilization of polyethylene terephthalate bottles.

A low-pressure microwave plasma reactor was developed for sterilization of polyethylene terephthalate (PET) bottles. In contrast to the established method using aseptic filling machines based on toxic sterilants, here a microwave plasma is ignited inside a bottle by using a gas mixture of nitrogen, oxygen, and hydrogen. To that effect, a reactor setup was developed based on a Plasmaline antenna allowing for plasma ignition inside three-dimensional packages. A treatment time below 5 s is provided for a reduction of 10(5) and 10(4) CFU of Bacillus atrophaeus and Aspergillus niger, respectively, verified by means of a count reduction test. The sterilization results obtained by means of this challenge test are in accordance with requirements for aseptic packaging machines as defined by the U.S. Food and Drug Administration and the German Engineering Federation. The plasma sterilization process developed here for aseptic filling of beverages is a dry process that avoids residues and the use of maximum allowable concentrations of established sterilants, e.g., hydrogen peroxide.

Spectroscopic characterization of an atmospheric pressure μ-jet plasma source

A new method for determination of plasma parameters under atmospheric pressure conditions is formulated and applied for characterization of a radio-frequency μ-jet plasma source using He/O2 mixture. By applying absolutely calibrated optical emission spectroscopy and numerical simulation, the gas temperature in the active plasma region and plasma parameters (electron density and electron distribution function) are determined. The steady-state concentrations of different species such as oxygen atom and ozone in the plasma channel and in the effluent of the plasma source are calculated using measured plasma parameters and gas temperature. On the other hand, spatial distribution of steady-state densities of these species are measured using emission and absorption spectroscopy. A comparison of the results thus obtained and the validation of the new method against two-photon absorption laser-induced fluorescence spectroscopy measurements are discussed. In addition, the influence of the surface processes and gas flow regime on the loss of the active species in the plasma source are discussed.