Papers

ICMCTF2006 Session G6: Coatings and Thin Films for Biomedical Applications

Wednesday, May 3, 2006 2:30 PM in Room Royal Palm 4-6

Wednesday Afternoon

Start	Invited?	Item
2:30 PM		G6-4 Bioactive Thin-Film Coatings: A Review S. Kumar (University of South Australia) Bioactive coatings with a variety of chemical compositions are being developed and used worldwide. What is expected of a bioactive coating is that when placed in physiological environments it is capable of exerting a specific biological response. The success of hydroxyapatite-coated orthopaedic and dental implants and the recent success of drug-eluting stents have provided a strong boost for the use and further development of bioactive coatings in a number of biomedical device sectors ranging from a variety of bioimplants through to antimicrobial surfaces. In the first part of this paper, the state-of-the-art of bioactive coatings science and technology will be reviewed and the emerging bioactive coating materials will be identified and briefly described. The second part of the paper will focus on the recent work done in the speaker's laboratory on bioactive thin-film coatings, that is, bioactive coatings which are thin films by definition (ab initio growth). Some of the case studies, mainly focused on orthopaedic implant applications, to be presented and discussed will be: solution and electro-deposited hydroxyapatite coatings loaded with biomolecules; plasma chemical vapor deposited silica coatings; plasma treatment of three-dimensional tissue engineering scaffolds; and plasma polymerised coatings with specific biofunctional groups. On the future of bioactive coatings, the speaker finds it hard to think of a medical device which cannot be improved by applying a coating. So this paper will be concluded by briefly explaining the newly coined term "Thin Film Is In".
3:10 PM		G6-6 Mechanical, Tribological, and Heamocompatibility Properties of ZrN-Ag, ZrN-Au, and ZrN-Pd Nanocomposite Films P. Basnyat, A. Aul, S.M. Aouadi, P. Kohli (Southern Illinois University); J. Xu, S.B. Mishra (University of Memphis); O. Eryilmaz, J.A. Johnson, A. Erdemir (Argonne National Laboratory) Nanocomposite films of ZrN-Me (Me = Ag, Au, or Pd) were produced by reactive unbalanced magnetron sputtering and their structural, chemical, mechanical, tribological and biocompatibility properties were studied as a function of film composition. The films formed a dense and homogeneous microstructure whereby nanocrystals of Me are distributed evenly throughout the ZrN matrix. The hardness and elastic modulii were found to depend on elemental composition and deposition parameters. Films produced with optimum deposition conditions were worn against ball-bearing steel using a ball-on-disk tribotester and were found to have superior tribological properties compared to ZrN. The heamocompatibility of the films was confirmed by investigating the adsorption of human serum albumin and fibrinogen using spectroscopic ellipsometry and atomic force microscopy.
3:30 PM		G6-7 Investigation of Mechanical and Biological Properties of Surfaces and Coatings Treated by Intense Ion Beams for In-body Applications¹ T.J. Renk, P.P. Provencio, S.V. Prasad, T.E. Buchheit (Sandia National Laboratories); T.J. Webster (Purdue University); T. Petersen (Alvarado Orthopedics); D.W. Petersen (University of Alabama (Birmingham)) We are investigating the microstructure, friction, and wear performance of surfaces and thin-film coatings exposed to pulsed intense ion beams for in-body applications such as hip and knee implants. Substrates of interest are Ti-6Al-4V, Co-Cr-Mo, and Zr alloy. An example of a surface-alloyed layer is a Hf-rich coating on nitrided Ti-6Al-4V for significantly improved wear performance as well as increased biocompatibility, compared to untreated Ti-6Al-4V. The treated layer exhibits a nanocrystalline grain structure. Coatings of nano-structured hydroxyapatite (HA) deposited on metal substrates are being studied for bone-ongrowth potential. Multi-layered ceramic and modified ceramic coatings (such as Al₂O₃/Y₂O₃) are also being investigated. Studies of treated layers will be presented, including compositional measurements (EDS, RBS), cross-sectional Transmission Electron Microscopy (TEM), and osteoblast (bone-forming cells) functional assays. The implications of ion-beam induced surface and microstructural changes on the tribological behavior will also be presented. ¹footnote 1@Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Co., under US DOE Contract DE-AC04-94AL85000.
3:50 PM		G6-8 Effect of Aluminum on the Corrosion Characterization of the NiTiAl Thin Film K.-T. Liu (National Tsing Hua University, Taiwan); J.G. Duh (National Tsing Hua Univerisity, Taiwan) An electrochemical study for the evaluation of corrosion behavior using potentiodynamic and Tafel techniques was conducted in 0.9% NaCl solution on Ni-Ti and Ni-Ti-Al shape memory thin films. A better corrosion resistance and lower current density were found for Ni-Ti-Al thin films rather than the Ni-Ti thin film. Atomic force microscopy (AFM) and field-emission electron probe microanalyzer (FE-EPMA) were applied to observe morphology of the surface film and elemental distribution prior to, and after immersion in 0.9% NaCl solution. The dissolution of Ni from Ni-Ti-Al thin films in the electrolyte, measured with inductively coupled plasma-atomic emission spectrometer (ICP-AES), reduced significantly after immersion for 7 days, as compared to Ni-Ti thin film. This result suggested that the improved corrosion performance of Ni-Ti-Al thin films would be beneficial for related potential biological application. This may be attributed to the introduction of aluminum and its specific properties, including the formation of a aluminum oxide layer after exposure to an aqueous environment.
4:10 PM		G6-9 Thin Coatings in Dental Application Against Fretting Wear C. Rapiejko, S. Fouvry (Ecole Centrale de Lyon, France); B. Grosgogeat (Universite Claude Bernard Lyon I, France); B. Wendler (Technical University of Lodz, Poland) Recent studies show that friction resistance between the arch-wire and the bracket contacts plays a critical role in the treatment quality. Indeed, high friction resistance induces overstressing which can damage the periodontal ligaments (i.e. the entire dentition is essentially joined to the surrounding bone through springs; namely the periodontal ligament). This generates fastidious and expensive clinical complications and for the worst cases (and specific patients) it could activate periodontal bacteria attack which, by destroying the periodontal ligaments will, generate an irreversible decohesion of the teeth. Moreever, friction will induce wear of the bracket and arch-wire materials which mainly consist of TiNi and stainless steels. This wear favors the spreed of heavy metal like Nickel through the body. The reduce such phenomena specific surface treatments have been developed. However a major difficulty comers the methodology to compare and improve the given palliatives. Have a specific fretting tool has been developed which permits the superimposition of micro slidings indeed by the occlusion movements and the macro slidings generated by the teeth displacement. This study evaluated the static friction force created between brackets and wires during combined Macro/Micro slidings. Various stainless steal bracket-arch wire contact have been analysed. Wear and frictions properties of different PECVD treatments such as γ -TiAl, SiC SiCN and TiAl64V thin coatings applied on the wire surface have been investigated. The chosen coatings are sufficiently resistant to wear and hemocompatible as wall as biocompatible. Test were run at a 5 N normal load and a 5 Hz frequency of with (+/- 50 µm) small amplitudes in superposed on 1mm global sliding. All tests have been performed under dry and wet artificial saliva medium.
4:30 PM		G6-10 In Vitro Corrosion and Wear-Corrosion Resistance of Pulsed Plasma Nitrided 304 AISI Stainless Steel M.H. Staia, C. Suarez (Central University of Venezuela) AISI Type 304 stainless steel has been the material of choice for the tubular components in dental and surgical instruments. However, this alloy has some drawbacks that limit its usefulness for instruments employed in the aggressive surgical procedures performed today. Among these drawbacks poor edge retention, poor wear resistance and poor galling resistance, all of which are desired in today’s instruments, could be mentioned. Plasma nitriding process at temperature lower than 400°C has claimed to mitigate against wear without imparing the corrosion resistance properties of these steels. Therefore, in this work, a study on the corrosion and wear-corrosion in a 3.5%NaCl behavior of a plasma nitrided 304 austenitic stainless steel has been carried out. The corrosion experiments were carried out by using electrochemical polarization in a standard cell. Sliding wear tests were conducted in a tribometer with an attachment able to carry the corrosive solution. The untreated substrate was also tested for comparison. The plasma ion nitriding process was performed at 400oC using a gas mixture composed of 80% N2 and 20% H2 for 30 and 40 minutes, respectively. The 30 minutes nitriding time allowed the formation at the steel surface of an expanded austenite phase (S-phase) accompanied by the presence of a small quantity of CrN. However, for a higher nitriding time, besides the S-phase, the formation of an incipient white layer composed of CrN and Fe4N took place. The results show that at low temperature and for 30 minutes the plasma nitriding can, to some extent, enhance the corrosion resistance of the 304 steel. However, when the nitriding time was increased to 40 minute, the corrosion resistance was of the same order of magnitud as the untreated steel. The corroded surface morphology was analyzed by SEM coupled with EDS.