Ondřej Kylián

Low pressure plasma discharges for the sterilization and decontamination of surfaces

The mechanisms of sterilization and decontamination of surfaces are compared in direct and post discharge plasma treatments in two low-pressure reactors, microwave and inductively coupled plasma. It is shown that the removal of various biomolecules, such as proteins, pyrogens or peptides, can be obtained at high rates and low temperatures in the inductively coupled plasma (ICP) by using Ar/O2 mixtures. Similar efficiency is obtained for bacterial spores. Analysis of the discharge conditions illustrates the role of ion bombardment associated with O radicals, leading to a fast etching of organic matter. By contrast, the conditions obtained in the post discharge lead to much lower etching rates but also to a chemical modification of pyrogens, leading to their de-activation. The advantages of the two processes are discussed for the application to the practical case of decontamination of medical devices and reduction of hospital infections, illustrating the advantages and drawbacks of the two approaches.

Substrate-Independent Approach for the Generation of Functional Protein Resistant Surfaces

A new route for coating various substrates with antifouling polymer layers was developed. It consisted in deposition of an amino-rich adhesion layer by means of RF magnetron sputtering of Nylon 6,6 followed by the well-controlled, surface-initiated atom transfer radical polymerization of antifouling polymer brushes initiated by bromoisobutyrate covalently attached to amino groups present in the adhesion layer. Polymer brushes of hydroxy- and methoxy-capped oligoethyleneglycol methacrylate and carboxybetaine acrylamide were grafted from bromoisobutyrate initiator attached to a 15 nm thick amino-rich adhesion layer deposited on gold, silicon, polypropylene, and titanium-aluminum-vanadium alloy surfaces. Well-controlled polymerization kinetics made it possible to control the thickness of the brushes at a nanometer scale. Zero fouling from single protein solutions and a reduction of more than 90% in the fouling from blood plasma observed on the uncoated surfaces was achieved. The feasibility of functionalization with bioactive compounds was tested by covalent attachment of streptavidin onto poly(oligoethylene glycol methacrylate) brush and subsequent immobilization of model antibodies and oligonucleotides. The procedure is nondestructive and does not require any chemical preactivation or the presence of reactive groups on the substrate surface. Contrary to current antifouling modifications, the developed coating can be built on various classes of substrates and preserves its antifouling properties even in undiluted blood plasma. The new technique might be used for fabrication of biotechnological and biomedical devices with tailor-made functions that will not be impaired by fouling from ambient biological media.

On the application of inductively coupled plasma discharges sustained in Ar/O2/N2 ternary mixture for sterilization and decontamination of medical instruments

Non-equilibrium low pressure-plasma discharges are extensively studied for their high potential in the field of sterilization and decontamination of medical devices. This increased interest in plasma discharges arises from, among other reasons, their capability not only to inactivate bacterial spores but also to eliminate, destroy or remove pathogenic biomolecules and thus to provide a one-step process assuring safety of treated instruments. However, recent studies have shown that optimal conditions leading to inactivation of spores and physical removal of pathogens differ significantly—the efficiency of spores sterilization is above all dependent on the UV radiation intensity, whereas high etching rates are connected with the presence of the etching agent, typically atomic oxygen. The aim of this contribution is to discuss and demonstrate the feasibility of Ar/N2/O2 low-pressure inductively coupled plasma discharges as an option to provide intense UV radiation while maintaining the high etching rates of biomolecules.

Sterilization and decontamination of medical instruments by low-pressure plasma discharges: application of Ar/O2/N2 ternary mixture

A low-pressure inductively coupled plasma discharge sustained in an argon–oxygen–nitrogen ternary mixture is studied in order to evaluate its properties in terms of sterilization and decontamination of surfaces of medical instruments. It is demonstrated by direct comparison with discharges operated in oxygen–nitrogen and oxygen–argon mixtures that application of an Ar/O2/N2 mixture offers the possibility to combine advantageous properties of the binary mixtures, namely, the capability of an O2/N2 plasma to emit intense UV radiation needed for effective inactivation of bacterial spores together with high removal rates of biological substances from Ar/O2 discharge. Moreover, optimal conditions for both effects are obtained at a similar ternary discharge mixture composition, which is of much interest for real applications, since it offers a highly effective process desired for the safety of medical instruments.

Elimination of biological contaminations from surfaces by plasma discharges: chemical sputtering.

Plasma treatment of surfaces as a sterilisation or decontamination method is a promising approach to overcome limitations of conventional techniques. The precise characterisation of the employed plasma discharges, the application of sensitive surface diagnostic methods and targeted experiments to separate the effects of different agents, have led to rapid progress in the understanding of different relevant elementary processes. This contribution provides an overview of the most relevant and recent results, which reveal the importance of chemical sputtering as one of the most important processes for the elimination of biological residuals. Selected studies on the interaction of plasmas with bacteria, proteins and polypeptides are highlighted, and investigations employing beams of atoms and ions confirming the prominent role of chemical sputtering are presented. With this knowledge, it is possible to optimize the plasma treatment for decontamination/sterilisation purposes in terms of discharge composition, density of active species and UV radiation intensity.

Low-pressure water vapour plasma treatment of surfaces for biomolecules decontamination

Decontamination treatments of surfaces are performed on bacterial spores, albumin and brain homogenate used as models of biological contaminations in a low-pressure, inductively coupled plasma reactor operated with water-vapour-based gas mixtures. It is shown that removal of contamination can be achieved using pure H2O or Ar/H2O mixtures at low temperatures with removal rates comparable to oxygen-based mixtures. Particle fluxes (Ar+ ions, O and H atomic radicals and OH molecular radicals) from water vapour discharge are measured by optical emission spectroscopy and Langmuir probe under several operating conditions. Analysis of particle fluxes and removal rates measurements illustrates the role of ion bombardment associated with O radicals, governing the removal rates of organic matter. Auxiliary role of hydroxyl radicals is discussed on the basis of experimental data. The advantages of a water vapour plasma process are discussed for practical applications in medical devices decontamination.

The Effect of Sterilization Processes on the Bioadhesive Properties and Surface Chemistry of a Plasma-Polymerized Polyethylene Glycol Film: XPS Characterization and L929 Cell Proliferation Tests

The influence of several sterilization processes (autoclaving, gamma-ray irradiation, ethylene oxide exposure and Ar/H(2) low pressure plasma treatment) on the surface chemistry and the bioadhesive properties of thin films (thickness approximately 20 nm) of plasma-polymerized diethylene glycol dimethyl ether has been studied. X-ray photoelectron spectroscopy (XPS) analysis and cell proliferation tests were used to characterize the surfaces. The XPS results revealed in all cases a change in the surface chemistry of the layer after sterilization, whereas the conservation of non-bioadhesive properties of the coating depends on the type of sterilization process. In particular, the low pressure plasma-based sterilization technique leads to a loss of the non-bioadhesive properties of the plasma coating, whereas the coatings are resistant to the other standard decontamination techniques. This property makes them suitable for biomedical applications, provided that an appropriate sterilization process is selected.

Deposition of amino-rich thin films by RF magnetron sputtering of nylon

RF magnetron sputtering of a nylon target in different gas mixtures was studied in order to evaluate the capability of this process to deposit amino-rich coatings needed in a wide range of biomedical applications. It has been demonstrated that both the deposition rate of the coatings and the surface density of primary amino groups are strongly linked with working gas mixture composition. From this point of view, a sufficiently high deposition rate as well as the highest amine efficiency reaching a NH2/C value of 18% was observed in the N2/H2 discharge, which leads to the surface exhibiting a high rate of protein adsorption.

Removal of immune-stimulatory components from surfaces by plasma discharges

Immune-stimulating microbiological components like lipopolysaccharide (LPS), lipoteichoic acid (LTA) and zymosan bound onto surfaces lead to severe problems when brought in contact with the organism via surgical instruments or implants. We have shown, in recent studies, that it is possible to detect different immune-stimulating components directly on the surface, via an indirect detection method, using human whole-blood and the monocyte reaction to measure the inflammatory mediator release (IL-1β) by ELISA. With regard to the inactivation of pyrogenic substances, we present a method based on the application of a low-pressure microwave plasma discharge working at low temperatures. We found a fast (10 s to a few minutes) removal rate of the immune-stimulating competence for LPS, LTA and zymosan. To mimic the bacterial cell-wall, LPS in combination with muramyl dipeptide was employed and the decreasing rate of the inflammatory signal did not differ from pure LPS.

Nylon-sputtered nanoparticles: fabrication and basic properties

Nylon-sputtered nanoparticles were prepared using a simple gas aggregation cluster source based on a planar magnetron (Haberland type) and equipped with a nylon target. Plasma polymer particles originated in an aggregation chamber and travelled to a main (deposition) chamber with a gas flow through an orifice. The deposited nanoparticles were observed to have a cauliflower-like structure. The nanoparticles were found to be nitrogen-rich with N/C ratio close to 0.5. An increase in rf power from 60 to 100 W resulted in a decrease in mean particle size from 210 to 168 nm whereas an increase in their residence time in the cluster source from 0.7 to 4.6 s resulted in an increase in the size from 73 to 231 nm.