Helmut Halfmann

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.

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.

Enhanced cell adhesion to silicone implant material through plasma surface modification

Silicone implant material is widely used in the field of plastic surgery. Despite its benefits the lack of biocompatibility this material still represents a major problem. Due to the surface characteristics of silicone, protein adsorption and cell adhesion on this polymeric material is rather low. The aim of this study was to create a stable collagen I surface coating on silicone implants via glow-discharge plasma treatment in order to enhance cell affinity and biocompatibility of the material. Non-plasma treated, collagen coated and conventional silicone samples (non-plasma treated, non-coated) served as controls. After plasma treatment the change of surface free energy was evaluated by drop-shape analysis. The quality of the collagen coating was analysed by electron microscopy and Time-Of-Flight Secondary Ion Mass Spectrometry. For biocompatibility tests mouse fibroblasts 3T3 were cultivated on the different silicone surfaces and stained with calcein-AM and propidium iodine to evaluate cell viability and adherence. Analysis of the different surfaces revealed a significant increase in surface free energy after plasma pre-treatment. As a consequence, collagen coating could only be achieved on the plasma activated silicone samples. The in vitro tests showed that the collagen coating led to a significant increase in cell adhesion and cell viability.

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.

Plasma mediated collagen-I-coating of metal implant materials to improve biocompatibility.

This study describes the collagen-I coating of titanium and steel implants via cold low-pressure gas plasma treatment. To analyze the coatings in terms of biocompatibility osteoblast-like osteosarcoma cells and human leukocytes were cultivated on the metal surfaces. Two different implant materials were assessed (Ti6Al4V, X2CrNiMo18) and four different surface properties were evaluated: (a) plasma pretreated and collagen-I coated implant materials; (b) collagen-I dip-coated without plasma pretreatment; (c) plasma treated but not collagen-I coated; (d) standard implant materials served as control. The different coating characteristics were analyzed by scanning electron microscopy (SEM). For adhesion and viability tests calcein-AM staining of the cells and Alamar blue assays were performed. The quantitative analysis was conducted by computer assisted microfluorophotography and spectrometer measurements. SEM analysis revealed that stable collagen-I coatings could not be achieved on the dip-coated steel and titanium alloys. Only due to pretreatment with low-pressure gas plasma a robust deposition of collagen I on the surface could be achieved. The cell viability and cell attachment rate on the plasma pretreated, collagen coated surfaces was significantly (p < 0.017) increased compared to the non coated surfaces. Gas plasma treatment is a feasible method for the deposition of proteins on metal implant materials resulting in an improved biocompatibility in vitro. (c) 2010 Wiley Periodicals, Inc. J Biomed Mater Res, 2010.

Determination of the electron energy distribution function via optical emission spectroscopy and a Langmuir probe in an ICP

Optical emission spectroscopy (OES) and Langmuir probe measurements are used to determine the electron density and the electron energy distribution function (EEDF) in an inductively coupled plasma (ICP) intended for sterilization of materials in medical applications. Measuring the EEDF with the Langmuir probe in the ICP discharge is limited to energies below 11 eV. Using OES the EEDF can be determined between 1.5 and 30 eV (in a He : N2 mixture). These methods are reliably compared in an ICP in a He : N2 mixture. Both diagnostics complement one another to determine the EEDF in a wide kinetic energy range.

Doppelt induktiv gekoppeltes Niederdruckplasma zur Sterilisation von medizinischen Implantatmaterialien / A double inductively coupled low-pressure plasma for sterilization of medical implant materials

Zusammenfassung Die Anwendungsmöglichkeiten der Plasmabehandlung werden im medizinischen Bereich erst allmählich bewusst. Die Inaktivierung von Keimen durch UV-Strahlung, die durch die Plasmaentladung generiert wird, sowie die Sterilisation medizinischer Implantatmaterialien und Instrumente stellt eine mögliche Anwendung dieser Technik dar. Darüber hinaus wird durch das Verfahren der Plasmatechnik die effiziente Kombination von Sterilisation mit einer Vielzahl von unterschiedlichen Beschichtungen bei medizinischen Implantatmaterialien ermöglicht. Um die Effektivität des Sterilisationsprozesses durch die Anwendung der Plasmatechnik bei verschiedenen Materialoberflächen zu untersuchen, wurden im Rahmen dieser Studie drei verschiedene Legierungen (X2CrNiMo18-15-3, Ti6Al7Nb und Ti6Al4V) und ein thermoplastischer Kunststoff [ultra high molecular weight polyethylene (UHMWPE)], welche in medizinischen Implantatmaterialien weit verbreitet sind, näher untersucht. Nach Sprühverkeimung der Prüfkörper aus den vier verschiedenen Implantatmaterialien (X2CrNiMo18-15-3, UHMWPE, Ti6Al7Nb und Ti6Al4V) mit Bacillus-athrophaeus-Sporen (106 KBE) konnte für jedes der vier getesteten Gasgemische (Ar, Ar:O2, Ar:H2 und Ar:N2) im Rahmen der durchgeführten Studie belegt werden, dass durch den Einsatz des neu entwickelten doppelt induktiven Niederdruckplasmas glatte medizinische Implantatmaterialien schnell, schonend und effizient sterilisiert werden können. Abstract The potential of plasma treatment in medicine is only slowly gaining acceptance. Inactivation of germs through exposure to UV radiation produced by plasma discharges and sterilization of medical implant devices and instruments is one possible application of this technique. In addition, due to the manifold possibilities of coating through plasma processes, quick sterilization-coating combinations of medical implant devices are possible. To analyze the effectiveness of this sterilization process on different material surfaces, three different alloys (X2CrNiMo18-15-3, Ti6Al7Nb and Ti6Al4V) and one thermoplastic material (ultra-high molecular weight polyethylene, UHMWPE), commonly used in medical implant devices, were examined in the presented study. After spraying Bacillus atrophaeus spores (106 CFU) on the surfaces of four different implant materials tested in this study (X2CrNiMo18-15-3, UHMWPE, Ti6Al7Nb and Ti6Al4V), it was demonstrated in each of four gas mixtures used (Ar, Ar:O2, Ar:H2 and Ar:N2) that due to the application of inductively coupled low-pressure plasma technique, plain medical implant materials can be sterilized rapidly, and can be protective and efficient.

Sterilization of heat-sensitive silicone implant material by low-pressure gas plasma.

BACKGROUND In recent years, plasma treatment of medical devices and implant materials has gained more and more acceptance. Inactivation of microorganisms by exposure to ultraviolet (UV) radiation produced by plasma discharges and sterilization of medical implants and instruments is one possible application of this technique. The aim of this study was to evaluate the effectiveness of this sterilization technique on silicone implant material. METHODS Bacillus atrophaeus spores (10(6) colony-forming units [CFUs]) were sprayed on the surfaces of 12 silicone implant material samples. Four plasma sets with different gas mixtures (argon [Ar], argon-oxygen [Ar:O(2)], argon-hydrogen [Ar:H(2)] and argon-nitrogen [Ar:N(2)]) were tested for their antimicrobial properties. Post-sterilization mechanical testing of the implant material was performed in order to evaluate possible plasma-induced structural damage. RESULTS The inductively coupled low-pressure plasma technique can achieve fast and efficient sterilization of silicone implant material without adverse materials effects. All four gas mixtures led to a significant spore reduction, and no structural damage to the implant material could be observed.

Oberflächenmodifikation metallischer Implantatmaterialien durch Niederdruckplasmabehandlung / Surface modification of metal implant materials by low-pressure plasma treatment.

Zusammenfassung Hintergrund: Die Plasmabehandlung medizinischer Implantatmaterialien führt zu einer Veränderung der Oberflächenenergie und der Benetzungseigenschaften von Materialien. Diese Veränderungen haben signifikanten Einfluss auf die Proteinadsorption sowie das Zellwachstumsverhalten auf der Materialoberfläche. Ziel der Studie war es, die plasmabedingten Veränderungen metallischer Implantatmaterialien quantitativ nachzuweisen und zu analysieren, ob durch eine Variation unterschiedlicher Einflussfaktoren wie Druck, Leistung, Gasmischung und Behandlungsdauer die Oberflächenenergie beeinflusst werden kann. Als weiteres Ziel sollte versucht werden, diese veränderten Oberflächeneigenschaften nutzbar zu machen und medizinische Implantate mit einer zellinduktiven Polyaminosäurebeschichtung zu versehen, um somit die Biokompatibilität der Materialien zu optimieren. Material und Methode: Drei medizinische Implantatmaterialien (X2CrNiMo18-15-3, Ti6Al4V und Ti6Al7Nb) wurden mit einem doppelt induktiv gekoppelten Niederdruckplasma behandelt. Nachfolgend wurde mittels Tropfenkonturanalyse ermittelt, ob eine Variation der verschiedenen Behandlungsparameter (Druck, Behandlungsdauer, Leistung, Gasmischung) Einfluss auf die Höhe sowie die zeitliche Beständigkeit der Oberflächenenergie hat. Des Weiteren wurden die behandelten sowie unbehandelten Implantatprüfkörper mit Kollagen-I beschichtet und anschließend rasterelektronenmikroskopisch analysiert. Ergebnisse: Die Plasmabehandlung steigerte die Oberflächenenergie aller Metalle deutlich. Bei der Veränderung der unterschiedlichen Behandlungsparameter zeigte sich, dass die Verlängerung der Behandlungszeit sowie die Erniedrigung des Behandlungsdruckes zu einer signifikant (p<0,05) langsameren Abnahmegeschwindigkeit der Oberflächenenergie führten. Die Beschichtungsversuche ergaben, dass nur auf den plasmabehandelten Metallen eine homogene Kollagenschicht aufgebracht werden konnte. Abstract Background: Plasma treatment leads to a significant change of surface free energy of medical implant materials. These changes strongly influence protein and cell adhesion on the material surface. The aim of the study was to quantify the plasma-induced surface changes and to analyse whether the change of treatment parameters, such as pressure, gas mixture, energy and treatment time, influences the surface free energy of the implant materials. To improve the biocompatibility of the surfaces, polyamino acid coating experiments were performed. Materials and methods: Three different metal implant materials (X2CrNiMo18-15-3, Ti6Al4V, Ti6Al7Nb) were treated with a double-inductively coupled low-pressure plasma. The influence of treatment parameter variation on the surface free energy was evaluated by drop shape analysis. The plasma treated and non-treated materials were incubated in collagen I solution. Afterwards, the coatings were analysed by electron microscopy in terms of structure and adhesion. Results: Drop shape analysis revealed that plasma treatment leads to a significant increase of surface free energy in all groups. Long plasma treatment times and low treatment pressures lead to a significant (p<0.05) extension of the detectable surface free energy increase. Coating experiments showed that only on plasma-treated samples solid and adherent collagen layers could be achieved.

Determination of argon resonance line emission in an ICP hitting a biological sample

A Monte Carlo model for the calculation of argon resonance line photon trapping in a double inductively coupled plasma is presented. Different probabilities of photon behaviour are calculated and the flux of photons hitting a target placed in the middle of the chamber is determined by simulation. Different gas admixtures or gas impurities can absorb photons or quench excited argon atoms, which is considered in the simulation. Electron energy distribution function and electron density are measured with a Langmuir probe and optical emission spectroscopy (OES). Nitrogen impurities, due to opening of the chamber, are measured using OES. These measured values and other additional input values such as gas temperature are used for simulation.