Papers

ICMCTF2003 Session G6/TS4-1: Coatings and Thin Films for Biomedical Applications

Thursday, May 1, 2003 8:30 AM in Room Sunrise

Thursday Morning

Start	Invited?	Item
8:30 AM		G6/TS4-1-1 ZrO₂ Oxidation Coatings onZr-Nb Knee Implant Condylar Components L.W. Hobbs (Massachusetts Institute of Technology); M. Spector (Brigham & Women's Hospital and Harvard Medical School); G. Hunter (Smith & Nephew, Inc.) Surface oxidation of a Zr-2.5Nb alloy is demonstrated to provide a resilient bearing surface on the femoral (condylar) component in a new total knee prosthesis which exhibits superior tribological properties articulating against polyethylene. Critical attributes of the self-coating oxide scale grown on the alloy are biological compatibility, hardness, surface smoothness, and adhesion to the substrate. Thermogravimetric, transmission electron microscopy and in situ hot-stage X-ray diffraction analysis of the oxide scale and underlying alloy substrate reveal the microstructural origins of the coating efficacy. The forged alloy in the condylar component exhibits a two-phase microstructure comprising elongated hexagonal α-Zr grains (< 1 wt% Nb) surrounded by cubic β-Nb (≤19 wt% Zr) sheath grains. During oxidation for times up to 8 hours in air at temperatures above and below the eutectoid at 620°C, interface control of oxidation kinetics occurs at the alloy/scale interface. The oxide scale predominantly comprises columnar grains of monoclinic ZrO₂, ~40 nm x 200 nm in size, with a strong [111] fiber texture and arranged in a brickwork pattern which is highly resistant to lateral fracture. The scale forms under substantial compression, up to -2 GPa in the surface plane, throughout the oxidation and cool down to room temperature. At the scale/alloy interface, unoxidized β-Nb fingers extend from the alloy into the oxide scale which appear to anchor the scale to the alloy. Later oxidation of this β-Nb second phase is associated with isolated outcrops of equiaxed oxide enhanced in Nb content and containing lamellar intergrowths of 6Zr0₂*Nb₂O₅. At the scale/oxygen interface lath-like separation into Zr-richer and Nb-richer oxides occurs which does not appear deleterious to the surface integrity of a polished scale.
9:30 AM		G6/TS4-1-4 Investigations on Fabrics Coated with Noble Metals using the Magnetron Sputter Technique with Regard to Antimicrobial Properties of the Thin Films J. Scholz, G. Nocke, W. Przyborowski, K. Matthess (University of Applied Sciences Zittau/Goerlitz, Germany); F. Hollstein, A. Weissbach (TECHNO-COAT Oberflaechentechnik GmbH, Germany) Fungal and microbial infestation can cause material damages on fabrics which become visible by discoloration and stains. Antimicrobially active coatings might be a possible protection against an infestation of the fabrics. In the presented investigations, fabrics consisting of glass fibers have been coated by noble metallic PVD-layers using the magnetron sputter technique in laboratory scale. The deposited layers were characterized according to bonding strength and antimicrobial effectiveness. Bonding strengths were measured by peel tests and microbial effectiveness by fouling experiments with regard to appropriate standardizations (DIN 53 931 and AATCC 30-19999). A plasma activation pretreatment of the fabrics is necessary for a sufficient bonding strength of the PVD-layers. The influence of some precursor gases on the surface activation of glass fiber fabrics is discussed in detail.
9:50 AM		G6/TS4-1-5 Composition and Adhesion of RF Magnetron Sputtering Deposited Calcium Phosphate Coatings on Different Substrates B. Feddes (University of Nijmegen, The Netherlands); A.M. Vredenberg (Utrecht University/Debye Institute, The Netherlands); J.G.C. Wolke, J.A. Jansen (University of Nijmegen) Calcium phosphate (CaP) coatings on implants are known to improve their biological performance. A good control of coating composition and adhesion is necessary for the development of medical applications. We studied the adhesion and composition of RF magnetron sputtering deposited CaP coatings. Coatings were deposited from a Ca₅(PO₄)₃OH target using an Ar plasma. Polyethylene (PE), polytetrafluoroethylene (PTFE) and Si substrates were used. The coating composition was determined using Rutherford Backscattering Spectrometry (RBS). The adhesion of the CaP on the polymeric substrates was studied using a microscratch tester. The influence of a 10 nm Ti interlayer on the adhesion was also studied. The coating composition depends strongly on the chosen substrate. We found a Ca/P ratio of 1-1.5 on PE, 1.5-2 on Si, and 2-6 on PTFE. The absolute amount of Ca in the coatings was the same, while the amount of P in the film was found to depend on the substrate. The difference between the PE and Si can be explained by a difference in charging of the surface, resulting from the varying conduction of Si and PE. The PE gets negatively charged nearby the RF discharge, which decelerates negative oxygen ions (originating from the target) that bombard the substrates. This causes less preferential resputtering of P. The high Ca/P ratio on PTFE results from a chemical effect. P reacts with fluorine which keeps escaping from the PTFE substrate during deposition, probably as a result of UV irradiation from the plasma. 1 µm thick CaP coatings on PTFE show bad adhesion. This was found to result from a weak layer within the PTFE, probably resulting from prolonged UV exposure during deposition. Micro scratch tests showed that a Ti interlayer strongly improves the adhesion of CaP on PTFE. On PE the opposite was found. A good adhesion was found for the as deposited CaP coatings, while a Ti interlayer made the adhesion worse.
10:30 AM		G6/TS4-1-7 CrBN Thin Films for Tribological and Biomedical Applications S.L. Rohde (University of Nebraska - Lincoln); S.M. Aouadi (Southern Illinois University); T.Z. Gorrishnyy (M.I.T.); D.M. Mihut, E. Schmatz (University of Nebraska - Lincoln) Metal Boron Nitride (MBN) thin films have sparked recent interest as very fine or even nanocrystalline thin films can be generated in these ternary alloy systems, which may have potential applications as biomedical, corrosion-resistant, tribological, and/or wear-resistant coatings. Previous studies have examined growth processes and resulting film properties for a limited range of CrBN and TiBN film compositions. The present work expands upon this and examines a wider array of CrBN film compositions from pure CrN to CrB₂ using ion-assisted unbalanced magnetron sputtering. Coatings were deposited over a range of temperatures from ambient (<20°C) to nearly 90°C, and their thermal stability investigated. Selected films were studied both in-situ and ex-situ using spectroscopic ellipsometry to determine their optical properties and provide correlation between the optical properties and chemical/structural changes in the films, providing a valuable resource for work in these new, but complex multi-phase materials. In addition, these films were characterized post-deposition using X-ray diffraction (XRD), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), infrared spectroscopic ellipsometry (IR-SE), nanoindentation, and microwear. XPS, AES, and IR-SE were used in tandem to reveal the crystal structure of the BN components in these ternary compounds. TA transition form crystalline, to nanocrystalline, to predominately amorphous film structures have been observed under specific growth conditions and in general the introduction of boron into the traditional transition metal nitrides results in marked grain size reductions.
10:50 AM		G6/TS4-1-8 Titanium Dioxide as a Surface to Mediate Reactive Inflammatory Species. J.J. Muyco (University of California, San Diego and Lawrence Livermore National Laboratory); R. Suzuki (University of California, San Diego); G. Hirata (University of California, San Diego and Centro Ciencia de Material Condensa, UNAM, Mexico); C. Orme (Lawrence Livermore National Laboratory); J.A. Frangos (La Jolla Bioengineering Institute); J. McKittrick (Univeristy of California, San Diego) Oxides of many metals are found in implants either as bulk ceramics or as a layer on metal implants. Observations of thin films of metal oxides and reactive species were made to further the understanding of the role of titanium dioxide (titania) in the acceptance of implants in the body. Titania is found on the surface of titanium implants, and is a potential biocompatibility enhancing coating material. Other metal oxides, such as aluminum oxide, that are in clinical use are used in this experiment for comparison. Interaction between metal oxides and reactive species involved in inflammation were observed using spectrophotometry and chemiluminescence to monitor the change in concentration of species of interest. The chemical data was correlated to surface phenomena obtained using surface characterization techniques. Peroxynitrite and superoxide were the inflammatory species used in this study. Rutile titania was found to have greater success in reducing the amount of synthetic peroxynitrite in solution than other metal oxides, including anatase titania. In contrast, anatase titania was best able to reduce the level of superoxide produced from stimulated macrophages. Surface characterization was done to correlate the ability to degrade superoxide and peroxynitrite to morphology and surface chemistry. Atomic force microscopy (AFM) studies that related the ability of titania to mediate inflammatory species to surface changes were one of the surface characterization techniques used. X-ray diffraction was also among techniques used; it verified the phases present on oxide surfaces. Acknowledgements: This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract number W-7405-Eng-48.