Papers

ICMCTF1999 Session E3: Coatings Resistant to Severe and Unusual Environments

Monday, April 12, 1999 8:30 AM in Room California

Monday Morning

Start	Invited?	Item
10:30 AM		E3-7 Graded Bioactive Coatings on Ti Implants A.P. Tomsia (Lawrence Berkeley National Laboratory) A new family of bioactive glasses has been developed with suitable thermo-mechanical properties to allow application as fixation agents between bone and titanium alloy biomedical implants. The glasses have thermal expansion coefficients closely matching those of Ti-based implant alloys while maintaining bioactivity in vitro. These new glasses are intended for use as bonding agents between Ti-based implants and bone; in fact, adherent, mechanically sound coatings of these glasses (thicknesses as high as 200 microns) have been deposited on titanium alloys. A firing schedule was developed that minimizes reactions and produces coatings with no cracks and good adhesion to the substrate. During firing a thin TiO layer formed on the Ti, preventing reaction between the glass and the metal. The best adhesion was obtained after firing at 800C for times up to 1 min. Longer times or higher temperatures resulted in dissolution of the oxide layer and reaction between the glass and the metal with formation of bubbles and weak interfaces. Interfacial indentation tests indicate that the glass and titanium form a bond with a high enough crack growth resistance to drive the crack out of the interface into the bioactive glass coating. As a result, to assure reliability of the implant/bone bond, the crack growth behavior of the bulk bioactive glasses as well as the Ti/glass interface must be clearly understood in the human physiological environment. Stress corrosion crack growth tests were performed under constant load on side-grooved double cantilever beam specimens. Initial investigations indicate the some of the new bioactive glasses show an improved subcritical crack growth resistance compared to the original Bioglass composition. Support is provided by the National Institute of Health under grant number NIH/NIDR #1R01DE11289.
11:10 AM		E3-9 Infection Resistant Biomimetic Coatings for Orthopedic Implants A. A. Campbell, L. Song, X. Li (Pacific Northwest National Laboratory) Medical device related infection results from introduction of organisms, primarily bacteria, during device insertion or implantation procedure, or from attachment of bloodborne organisms to newly inserted device. Good clinical practice-such as thoroughly cleaning and disinfecting the area prior to insertion, proper prepping by clinical staff, and care in handling device to maintain sterility prior to insertion will reduce the occurrence of infection. Most bacteria that cause device related infections enter the body when device is placed. The organism first attaches the device and after the attachment, they grow further to form microcolonies and create a protective barrier commonly known as biofilm. The goal of this work was to produce calcium phosphate coatings that were infection. Our work to date is focused on the evaluation of antimicrobial agents, such as chlorhexadiene that are incorporated into mineral surface. The efficacy of the coatings will be evaluated in a goat model and comparisons made with uncoated pins, ion deposited silver-coated pins, and dip coated chlorohexadine pins.
11:30 AM		E3-10 Tribological Properties of Coatings for Hip Joint Prostheses A.H.S. Jones (Teer Coatings, Ltd., United Kingdom); D.G. Teer (Teer Coatings Ltd., Hartlebury Trading Estate, Worcestershire, United Kingdom) It is reported (1) that CoCr hip joint prostheses exhibit low wear and hence have long life. Reciprocating wear tests have been performed by rubbing CoCr against CoCr both dry and under de-ionised water in order to obtain basic friction and wear data. Similar tests have been performed using coated pins and coated discs. The coatings studied have included typical hard coatings such as TiN and a recently developed carbon based coating(2). Typical hard coatings offered no improvement when compared to the uncoated samples. In contrast, the new carbon coatings are shown to have exceptional tribological properties under both dry and lubricated rubbing. The under water tests indicate that the wear rate of CoCr can be reduced by about 100X This appears to offer the possibility of significant improvements in the useful life of hip joint prostheses. ¹R.M. Streicher, M. Semlitsch, R. Schon, H. Weber and C. Rieker. Metal-on-Metal Articulation for Artificial Hip Hoints: Laboratory Study and Clinical Results. Advances in Medical Tribology, Ed. D. Dowson, M.E.P. Ltd. London 1998, pp. 83-92. ²D. Camino, A.H.S. Jones, D. Mercs and D.G. Teer. High Performance Sputtered Carbon Coatings for Wear Resistant Applications. To be published Vacuum
11:50 AM		E3-11 Effect of Carbon Overcoat Film Coverage on Corrosion Protection of Magnetic Thin Film Disks. J. Edwards, W.J. Chia, C. Wang (Western Digital Corp.); M. Geisler (Balzers Process Systems, GmbH, Germany) Carbon overcoats are used in magnetic recording to protect the magnetic film from degradation by both corrosion and wear resulting from contact with the read / write head. Disk areal density is unfortunately limited by the head-media spacing. A continuing drive exists to reduce carbon overcoat thickness for improved magnetic performance. Characterization of the corrosion protection of sputtered carbon doped with hydrogen gas [CH], sputtered carbon doped with nitrogen and hydrogen gases [CHN], and pecvd hydrogenated carbon [CH] was performed. Disks with 20-100 Å carbon overcoats were subjected to a hot-wet environment for four days. The amount of cobalt which could then be washed off the disk was quantified by ICP mass spectroscopy. The authors maintain superior corrosion protection is derived from better surface coverage. It was found that surface roughness plays a primary role in corrosion protection. Overcoat thickness also plays a strong role below 60 Å. The critical overcoat thickness required to protect against corrosion avalanche appears to be a function of the film nucleation density for each composition. CH has a thinner critical thickness than CHN. The unique mode of deposition of the pecvd source makes this a more corrosion-resistant layer than the sputtered layers.