Karsten Schröder

Atmospheric pressure plasma: a high-performance tool for the efficient removal of biofilms.

Introduction The medical use of non-thermal physical plasmas is intensively investigated for sterilization and surface modification of biomedical materials. A further promising application is the removal or etching of organic substances, e.g., biofilms, from surfaces, because remnants of biofilms after conventional cleaning procedures are capable to entertain inflammatory processes in the adjacent tissues. In general, contamination of surfaces by micro-organisms is a major source of problems in health care. Especially biofilms are the most common type of microbial growth in the human body and therefore, the complete removal of pathogens is mandatory for the prevention of inflammatory infiltrate. Physical plasmas offer a huge potential to inactivate micro-organisms and to remove organic materials through plasma-generated highly reactive agents. Method In this study a Candida albicans biofilm, formed on polystyrene (PS) wafers, as a prototypic biofilm was used to verify the etching capability of the atmospheric pressure plasma jet operating with two different process gases (argon and argon/oxygen mixture). The capability of plasma-assisted biofilm removal was assessed by microscopic imaging. Results The Candida albicans biofilm, with a thickness of 10 to 20 µm, was removed within 300 s plasma treatment when oxygen was added to the argon gas discharge, whereas argon plasma alone was practically not sufficient in biofilm removal. The impact of plasma etching on biofilms is localized due to the limited presence of reactive plasma species validated by optical emission spectroscopy.

Pulsed and cw microwave plasma excitation for surface functionalization in nitrogen-containing gases

Abstract Results are presented of polymer surface functionalization processes in pulsed and continuous wave (cw) microwave-excited plasmas in nitrogen-containing gases under admixture of hydrogen. A maximum selectivity of 100% for amino groups with respect to all nitrogen functional groups (NH 2 /N) was obtained in cw microwave (MW) plasmas either for very short treatment durations below 100 μs in pure NH 3 , or within approximately 10 s in hydrogen-rich nitrogen-containing plasmas. The amino and overall nitrogen surface densities, NH 2 /C and N/C, reach up to 3.5% and 35%, respectively. Post plasma processes of functionalized polymers are discussed in the light of monofunctionalization. Down to pulse duration of 1 ms, plasma decomposition rates of NH 3 , determined by infrared absorption spectroscopy, are found to scale linearly with the duty cycle. In this regime, the main effect of a duty cycle variation in pulsed NH 3 plasmas on surface functionalization can be interpreted to result from changes in the concentration of the dominant stable species in the gas phase, NH 3 , N 2 and H 2 , which are activated by subsequent plasma pulses. With increasing duty cycle, NH 3 decomposition to N 2 and 3H 2 more and more dominates over the supply of fresh NH 3 . The nitrogen-removing role of hydrogen in the plasma is discussed in detail, whereas the role of the numerous transient nitrogen-containing species remains to be studied in the future.

On the Applicability of Plasma Assisted Chemical Micropatterning to Different Polymeric Biomaterials

A plasma process sequence has been developed to prepare chemical micropatterns on polymeric biomaterial surfaces. These patterns induce a guided localized cell layover at microscopic dimension. Two subsequent plasma steps are applied. In the first functionalization step a microwave ammonia plasma introduces amino groups to obtain areas for very good cell adhesion; the second passivation step combines pattern generation and creation of cell repelling areas. This downstream microwave hydrogen plasma process removes functional groups and changes the linkages of polymer chains at the outermost surfaces. Similar results have been obtained on different polymers including polystyrene (PS), polyhydroxyethylmethacrylate (PHEMA), polyetheretherketone (PEEK), polyethyleneterephthalate (PET) and polyethylenenaphthalate (PEN). Such a rather universal chemical structuring process could widen the availability of biomaterials with specific surface preparations.

Capability of Differently Charged Plasma Polymer Coatings for Control of Tissue Interactions with Titanium Surfaces

Titanium surfaces were equipped with positively and negatively charged chemical functional groups by plasma polymerization. Their capability to influence the adhesion of human mesenchymal stem cells (hMSCs) and inflammation processes was investigated on titanium substrates, which are representative of real implant surfaces. For these purposes, titanium samples were coated with plasma polymers from allylamine (PPAAm) and acrylic acid (PPAAc). The process development was accompanied by physicochemical surface analysis using XPS, FT-IR and contact angle measurements. Very thin plasma polymer coatings were created, which are resistant to hydrolysis and delamination. Positively charged amino groups improve considerably the initial adhesion and spreading steps of hMSCs. PPAAm and PPAAc surfaces have an effect on the differentiation of hMSCs, e.g., the expression of osteogenic markers in dependence on culturing conditions. Acrylic acid groups appear to stimulate early mRNA differentiation markers (ALP, COL, Runx2) under basal conditions, whereas positively and negatively charged groups both stimulate late differentiation markers, like BSP and OCN, after 3 days of osteogenic stimulation. Long-term intramuscular implantation in rats revealed that PPAAc surfaces caused significantly stronger reactions by macrophages and antigen-presenting cells compared to untreated control (polished titanium) samples, while PPAAm films did not show a negative influence on the inflammatory reaction after implantation.

Cytocompatibility of amorphous hydrogenated carbon nitride films deposited by CH4/N2 dielectric barrier discharge plasmas with respect to cell lines

Special amorphous hydrogenated carbon nitride (a-H–CNx) films have been prepared on glass substrates for the investigation of adhesion and proliferation of different mammalian cell lines. CH4/N2 dielectric barrier discharge plasmas were applied to deposit a-H–CNx coatings at half of the atmospheric pressure. Film quality was modified by varying the CH4:N2 ratio and deposition duration. Chemical composition was determined by x-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy. The N/C ratio was in the range of 0.20–0.55. A very small surface roughness was verified by atomic force microscopy. Human embryonic kidney (HEK) and rat adrenal pheochromocytoma (PC12) cells were cultivated on the a-H–CNx films to investigate the cytocompatibility of these surfaces. The microscopic images show that both kinds of cells lines were unable to survive. The cells did not adhere to the surfaces, and most of the cells died after certain time spans. Increased amounts of nitrogen in the film induce ...

Hydrophobic coatings deposited with an atmospheric pressure microplasma jet

Successful plasma polymerization of a fluorocarbon compound (c-C4F8) using an atmospheric pressure plasma jet is described. The source is operated with argon as working gas at a flow rate of 6 slm and 10–100 sccm admixtures of c-C4F8. Deposition is limited to a discharge regime with strong localization and was observed for conductive substrates only (Al and Si). The deposition process is characterized by a high local growth rate (40 nm s−1) and produces films which show a Teflon-like chemical structure and hydrophobicity. The coatings are characterized using x-ray photoelectron spectroscopy, profilometry and scanning electron microscopy. Changing the ambient atmosphere from protective N2 to normal air only reduces the deposition rate but does not change the chemistry of the film.Based on the results of parameter variations and the electrical relations of the jet setup, the special form of the deposition regime of the jet is discussed and considered to be a γ-mode discharge dependent on the choice of substrate material.

On the Use of Atmospheric Pressure Plasma for the Bio-Decontamination of Polymers and Its Impact on Their Chemical and Morphological Surface Properties

Low temperature atmospheric pressure plasma processes can be applied to inactivate micro-organisms on products and devices made from synthetic and natural polymers. This study shows that even a short-time exposure to Ar or Ar/O2 plasma of an atmospheric pressure plasma jet leads to an inactivation of Bacillus atrophaeus spores with a maximum reduction of 4 orders of magnitude. However, changes in the surface properties of the plasma exposed material have to be considered, too. Therefore, polyethylene and polystyrene are used as exemplary substrate materials to investigate the effect of plasma treatment in more detail. The influence of process parameters, such as type of operating gas or jet-nozzle to substrate distance, is examined. The results show that short-time plasma treatment with Ar and Ar/O2 affects the surface wettability due to the introduction of polar groups as proofed by X-ray photoelectron spectroscopy. Furthermore, atomic force microscopy images reveal changes in the surface topography. Thus, nanostructures of different heights are observed on the polymeric surface depending on the treatment time and type of process gas.

Gas-Discharge Plasma-Assisted Functionalization of Titanium Implant Surfaces

A crucial factor for in-growth of metallic implants in the bone stock is the rapid cellular acceptance whilst prevention of bacterial adhesion on the surface. Such contradictorily adhesion events could be triggered by surface properties. There already exists fundamental knowledge about the influence of physicochemical surface properties like roughness, titanium dioxide modifications, cleanness, and (mainly ceramic) coatings on cell and microbial behavior in vitro and in vivo. The titanium surface can be equipped with antimicrobial properties by plasma-based copper implantation, which allows the release and generation of small concentrations of copper ions during contact with water-based biological liquids. Additionally, the titanium surface was equipped with amino groups by the deposition of an ultrathin plasma polymer. This coating on the one hand does not significantly reduce the generation of copper ions, and on the other hand improves the adhesion and spreading of osteoblast cells. The process development was accompanied by physicochemical surface analyses like XPS, FTIR, contact angle, SEM, and AFM. Very thin modified layers were created, which are resistant to hydrolysis and delamination. These titanium surface functionalizations were found to have either an antimicrobial activity or cell-adhesive properties. Intramuscular implantation of titanium samples coated with the cell-adhesive plasma polymer in rats revealed a reduced inflammation reaction compared to uncoated titanium.

Similarities between Plasma Amino Functionalized PEEK and Titanium Surfaces Concerning Enhancement of Osteoblast Cell Adhesion

The application of gas discharge plasmas for different functionalization and coating strategies is discussed with respect to cell adhesion to polymeric and metallic surfaces. Poly(ether ether ketone) (PEEK) and titanium (Ti) were selected as typical bone cell-contacting biomaterials. The surfaces were equipped with nitrogen-based chemical functionality, mainly amino groups. The behavior of human MG-63 osteoblasts was investigated with respect to cell adhesion and growth on plasma-treated PEEK and Ti surfaces. MG-63 cells adhere faster and occupy a wider cell area on the plasma-treated compared to untreated surfaces, which is not integrin receptor mediated. Although different plasma treatments were applied to functionalize polymeric and metallic surfaces with amino groups, similar cell adhesion properties were achieved.

Cancer cells (MCF-7, Colo-357, and LNCaP) viability on amorphous hydrogenated carbon nitride film deposited by dielectric barrier discharge plasma

Atmospheric pressure dielectric barrier discharge plasma in CH4/N2 (1:1) gas mixture has been employed to deposit amorphous hydrogenated carbon nitride (aH–CNx) film. In vitro studies with three different cancer cell lines were carried out on the coated surfaces. Preliminary biocompatibility and effect of CH4/N2 films have been investigated by measuring cell proliferation. Three different cancer cell (MCF-7, Colo-357, and LNCaP) suspensions have been exposed on the surface of aH–CNx film to investigate the effect of deposited films on viability of cells. Results from the MTS (3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H- tetrazolium, inner salt) proliferation assays indicated that the deposited aH–CNx film is cytotoxic to cancer cell lines. Time course cell viability assay indicated maximum cell death at 24 h after seeding the cells. This effect is dependant on physicochemical and mechanical properties of the deposited films. The deposited film has been characterized by x-r...