ICMCTF2005 Session G6-1: Coatings and Thin Films for Biomedical Applications

Thursday, May 5, 2005 8:30 AM in Room California

Thursday Morning

Start	Invited?	Item
8:30 AM		G6-1-1 Integrated Tribo-SPM Nano-Micro-Metrology of Thin Films N.V. Gitis, A. Daugela, S. Kuiry (Center for Tribology, Inc.) Performance of a quantitative nano+micro thin-film tester mod. UNMT, integrated with SPM and high resolution optical microscope imaging, is demonstrated on semiconductor wafers and flat panel display samples, where quantitative materials properties were derived at several intermediate characterization steps by means of nano-indenting and micro-scratching modules. The load ranges of these modules are 5 nN to 500 mN for the nanoindenter and 0.5 mN to 50 N for the micro-scratcher. The instrument can extract mechanical properties and surface topography at intermediate steps of thin-film testing and is filing the gap between microscale tribology test and nanoscale characterization metrology. A copper layer workhardening effect has been studied on the nanoiondentation loading-unloading curves for the Cu coated Si wafer sample. Durability of ultra-thin DLC layers on flat panel display has been studied on different polymer substrates with different pre-treatments.
8:50 AM		G6-1-2 Electrostatic Deposited Coating of Nanostructured Hydroxyapatite (HAp) Coating for Biomedical Applications W. Jiang (NanoMech LLC); G. Nyandoto, L. Sun, A.P. Malshe (University of Arkansas) Hydroxyapatite, a calcium phosphate ceramic, is chemically similar to bone mineral and one of the few materials able to produce direct-bonding osteogenesis. Nanostructured hydroxyapatite coating has proved effective in promoting cell growth. However, synthesis of the coating on components of complex geometries with controlled phases is still a challenge. In this paper, we present the results from the exploration of electrostatic self-assembled coating of hydroxyapatite nanoparticles and the interaction of particles with laser. The nanoparticles were deposited on commercial grade titanium alloy and bonded using a transient laser heating process. The coating was characterized for its surface morphology, particle size, and adhesion, and analyzed for its chemical compositions. Results have shown the potential of this process to address some of the issues present in the current synthesis processes.
9:10 AM		G6-1-3 Anodic Thin Films on Titanium used as Masks for Surface-Micropatterning of Biomedical Devices Ch Jaggi, P. Kern (Swiss Federal Institute for Materials Testing and Research (EMPA), Switzerland); J. Michler (Swiss Federal Laboratories for Materials Testing and Research (EMPA), Switzerland); T. Zehnder (Ion Beam Analysis Center, Switzerland); H. Siegenthaler (University of Bern, Switzerland) Ceramic oxide films like titanium dioxide are used on medical implants to improve biocompatibility and corrosion behaviour. Besides chemical composition, the topography of implants with surface features in the tens of micron range is known to promote osteointegration.¹ In this work, the potential of anodically grown TiO₂ thin films as mask material for electrochemical micro/nanopatterning of medical implant surfaces sensitized by ion beam, electron beam and laser irradiation is investigated. Electrochemical Impedance Spectroscopy (EIS) was used to characterize resistance and capacitance of oxide films anodized under various conditions. The resistance obtained by fitting to an appropriate equivalent circuit was compared to the film stability in electrochemical pitting experiments. Ellipsometry and Raman measurements were performed for accurate thickness determination and phase characterization, respectively. The film topography was analyzed via SEM and AFM. Film composition was analyzed via GDOES, RBS, ERDA, XPS and TEM. An increasing film resistance was found to correlate to increasing pitting resistance. GDOES revealed an accumulation of hydrogen at the oxide/metal interface. The GDOES depth profiles were also compared to ERDA data for validation. Based on the performance in pitting tests, thin amorphous as well as thin anatase TiO₂ thin films were used for subsequent micropatterning experiments. After electron beam irradiation a preferential dissolution of non-irradiated areas could be achieved. Laser treatment led to preferential etching of the irradiated sites. Both preferential and reduced dissolution was observed in case of ion beam irradiation. Potential physico-chemical mechanisms for the micropatterning effects are discussed. ¹ D. Buser et al., Biomed. Mat. Res., 25, (1991), 889.
9:30 AM		G6-1-4 Surface Modification and Thin-Film Formation by Intense Ion Beams for In-Body Applications¹ T.J. Renk, P.P. Provencio, S.V. Prasad, T.E. Buchheit (Sandia National Laboratories); D.W. Petersen (University of Alabama (Birmingham)) We are investigating the microstructure, friction, and wear performance of surfaces and modified 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 Ultra-High Molecular Weight Polyethylene (UHMWPE). An example of a surface-alloyed layer is a Hf-rich coating on Ti-6Al-4V that has been shown to produce significantly improved wear performance as well as increased biocompatibility, compared to untreated Ti-6Al-4V. The treated layer exhibits a nanocrystalline grain structure. It may be possible to harden the UHMWPE by cross-linking induced by ion beam thermal processing. Ceramic and modified ceramic coatings are also being investigated. Studies of treated layers will be presented, including compositional measurements (EDS, RBS), and cross-sectional Transmission Electron Microscopy (TEM). The implications of ion-beam induced surface and microstructural changes on the tribological behavior will be presented. ¹Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Co., under US DOE Contract DE-AC04-94AL85000.
9:50 AM		G6-1-5 Low-Temperature Plasma Deposition of Silica Thin Films for Bio-Functionalisation of Biomedical Implant Materials S. Kumar (University of South Australia) Surface coating and bio-functionalisation of biomedical implant materials is a topical area of research aimed at achieving improved implant (prosthesis) fixation. In the area of bone implants, for example, bio-functional groups such as silanol (Si-OH), carboxyl (COOH) and hydroxyl (OH) have been identified as promoters of nucleation and growth of apatites (such as carbonated and hydroxy) from simulated body fluids onto various types of biomedical substrates. In this paper, we present the results obtained on bio-functionalisation of both metallic (titanium and surgical stainless steel coupons) and polymeric (PLGA, a biodegradable three-dimensional polymeric tissue enginering scaffold) materials with silanol functional groups. These Si-OH functional groups are obtained by coating the materials in question with a thin film of hydrated silica by using the technique of low-temperature radio-frequency plasma deposition, with tetraethoxysilane as the main precursor. The silica coatings thus obtained have been demonstrated to be near-stoichiometric as revealed by X-ray photoelectron spectroscopy (XPS) and conformal to the substrate morphology as investigated by scanning electron microscopy (SEM) and profilometry. The XPS and SEM investigations of the silica-coated three-dimensional PLGA scaffold samples reveal that both the surface and the bulk of the samples get coated, with relativley more silica deposition on the surface. Reduced fibrinogen adsorption onto silica-coated titanium substrates as compared to bare titanium controls suggests that the silica thin films in question are likely to exhibit anti-inflammatory behaviour. The plasma based coating/bio-functionalisation strategy discussed in this paper can also be utilised for imparting mechanical stability and bioactivity to otherwise fragile and bio-inert large 3-D PLGA scaffold constructs, with attendant sterilisation.
10:10 AM	Invited	G6-1-6 Amorphous Diamond Coatings for Biomedical Applications R. Lappalainen (University of Kuopio, Finland) Most of the biomedical applications can be divided into two characteristic components: bulk material, which mainly is responsible for the mechanical and structural properties; and surface layer material, which interacts with the biologic environment. The idea of surface modification or coating is to retain the desired bulk properties while modifying only the outermost surface. Because high quality amorphous diamond coatings deposited using ion or plasma beams are biocompatible, chemically inert, extremely hard and wear resistant, they are very potential to improve surface characteristics. However, biomedical applications are normally in very severe and demanding environment especially in long-term use. Therefore, the coating should last even a lifetime without significant wear or delamination. This review will show that this is a challenging task. Amorphous diamond coatings must fulfill several requirements: high adhesion of the coating to the substrate, good corrosion resistance in biological fluids and high quality and surface finish. To achieve these goals, typically special procedures such as combination of different techniques, high deposition energies, intermediate layers or laminated structures are needed. Due to extreme properties of diamond, the coatings can improve corrosion and wear resistance even by a factor of million compared to conventional materials. This is a major advantage, e.g. in articulation surfaces of artificial joints, in bone screws or in implant fixation straight to living tissues or with bone cement. On the other hand, inertness and biocompatibility are important features in contact with body fluids like blood or saliva, e.g. in heart valves and teeth implants.
10:50 AM		G6-1-8 Multiwalled Carbon Nanotube/Polymer Nanocomposites As Biomimetic Artificial Muscles D.Y. Lee (Daelim College of Technology, South Korea); M.-H. Lee (Korea Institute of Ceramic Engineering and Technology, South Korea); K.J. Kim, S. Heo (University of Nevada); B.Y. Kim (Daelim College of Technology, South Korea); S.J. Lee (Kyungsung University, South Korea) The increased demand for highly active biomimetic actuators producing high power densities and large force generation capacities in the range of microswitches to artificial muscles has fueled the development of a large variety of material systems to achieve the maximum allowable operation temperature, the need for high voltages and limitation on work density per cycle. This has spurred the development of CNT/polymer composites due to actuation threshold at considerably low doping levels (<5 wt.%) of CNTs and no relaxation of the cantilever tip. In the present study, the multiwalled nanotube(M-CNT)-Nafion polymer composites are prepared by a method of casting because the synthesis of M-CNT is highly advanced to improve its quality and quantity and to satisfy many needs. The composites are then examined by XRD, FESEM/EDS, particle size analyzer, TEM, TG/DSC, elastic modulus and blocking force measurement to evaluate the influence of M-CNT dispersion in polymer matrix and M-CNT content on actuation properties of the composites.
11:30 AM		G6-1-10 Electrochemical Impedance Spectroscopy Studies of TiAlN and TiN Films on Ni-Based Alloys Under Biological Media K.-T. Liu, J.G. Duh (National Tsing Hua University, Taiwan); K.H. Chung (Institute of Oral School of Density, Taiwan); J.H. Wang (Chunghwa Telecom Co. Ltd., Taiwan) The conventional Ni-based alloys have been associated with adverse tissue reactions and hypersensitivity reactions in oral cavity. In this study, TiN and TiAlN were deposited on Ni-based alloys by RF sputtering technique. Electrochemical impedance spectroscopy was employed as in-situ techniques to observe the evolution of the TiN and TiAlN film on exposure in biological media. After immediate- to short-term exposure, the biological media was investigated with inductively coupled plasma-atomic emission spectrometer (ICP-AES) to evaluate the release of metal ions, such as nickel, chromium, and cobalt. The results of ICP - AES analysis showed that TiN and TiAlN coated on Ni-based alloys effectively reduced metal ion release levels, as compared to the uncoated Ni-based alloys. The effect of the nitride films was also reflected in corrosion resistance and the corrosion rate. A higher corrosion resistance was revealed for the TiN and TiAlN coated Ni-based alloys as compared to uncoated substrates. Furthermore, the impedance of nitride films on Ni-based alloys was larger than that of metalâ?Ts charge transfer reaction at short-term immersion. Key words: Ni-based alloys, Electrochemical Impedance Spectroscopy, TiN, TiAlN films, ICP-AES, Corrosion Resistance, Impedance.
11:50 AM		G6-1-11 Coating of Ni-based Dental Alloys with TiN and TiAlN and its Effect on Attachment and Spreading of Cells G.-T. Liu, J.G. Duh (National Tsing Hua University, Taiwan); K.H. Chung (Institute of Oral School of Density, Taiwan) The TiN and TiAlN coatings were fabricated by RF sputtering on the commercial Ni-based alloys. The cell culture with various periods was employed to evaluate the biocompatibility of the surface-modified Ni-based dental alloys. After long time cultured, the release of nickel ion was measured with inductively coupled plasma-atomic emission spectrometer (ICP-AES) in the media. The depth profile of nickel diffusion through the nitride films was analyzed with Auger electron spectroscopy. The films coated on Ni-based dental alloys effectively retarded the nickel released level in the media, as compared with uncoated Ni-based dental alloys. The cell morphology and cell density were examined using scanning electron microscopy. Sufficient adhesion of cell to TiN and TiAlN films was observed, and the cells were well spreaded on the surface-modified materials. On the contrary, a large proportion of cells seemed to be rounded and poorly attached on the Ni-based dental alloys. These distinctions would be discussed with respect to the surface properties, metal ion release and roughness.