Papers

ICMCTF2009 Session TS3-1: Bioactive Coatings and Surface Biofunctionalization

Monday, April 27, 2009 1:30 PM in Room Sunset

Monday Afternoon

Start	Invited?	Item
1:30 PM		TS3-1-1 Nitrogen-Rich Plasma Polymer Coatings ("PPE:N") for Bio-Medical Applications in Orthopaedic and Vascular Therapies M.R. Wertheimer, P.L. Girard-Lauriault, F. Truica-Marassescu, J.-C. Ruiz (École Polytechnique, Canada); H.T. Wang, J. Antoniou, F. Mwale (McGill University, Canada); S. Lerouge (Notre-Dame Hospital, Canada) We have recently reported that nitrogen (N)-rich (amine-bearing) polymer surfaces can promote cell adhesion and influence processes such as differentiation of stem cells. A well-known route for obtain-ing high nitrogen concentrations, [N], is plasma-polymerisation (PP) of suitable N-containing “monomers” (e.g. allyl-amine). In this study, however, we used binary gas mixtures of varying ratios, X, comprising ethylene and nitrogen or ammonia, and we compared the physico-chemical properties of our “PPE:N” films, which were deposited either in conventional low-pressure (“L-PPE:N”) r.f. glow discharges, or in a dielectric barrier discharge (DBD) reactor operating at atmospheric (“H-PPE:N”) pressure. Both types of deposits were characterised by several analytical techniques, such as X-ray Photoelectron Spectroscopy (XPS), Infrared Spectroscopy (IR), and Near-edge X-ray Absorption Fine Structure (NEXAFS), to determine their surface-chemical compositions and molecular structure; and Contact Angle Goniometry (CAG) for evaluating their surface energies. Various N-containing species were identified by combining complementary analyses; for example, the concentration of primary amines was determined by the selective reaction of 4-(trifluoromethyl)benzaldehyde (TFBA) vapour with the surface-near (-NH2) groups, while XPS, IR and NEXAFS allowed semi-quantitative analyses of unsaturated species such as nitriles, iso-nitriles and imines to be carried out. XPS data revealed [N] values of up to 40 at.-%, primarily comprising nitrile and amine functionalities, where [N] could be controlled systematically and reproducibly by varying X. PPE:N-coated substrates have already proven their value in several bio-technological applications: for example, usually non-adherent human U-937 monocytes could readily adhere to them, as did chondrocytes, human mesenchymal stem cells (MSC), vascular smooth muscle cells (VMSC), and other cell lines of interest in orthopaedics and in vascular medicine. Furthermore, we demonstrated the existence of [N]crit values, below which different cell lines ceased to adhere, that MSC differentiation could be regulated, and that resistance to apoptosis of VMSC could be increased. In several of these situations, for example in studying U-937 and MSC, we have carried out detailed experiments using reverse transcriptase-polymerase chain reaction (RT-PCR) to investigate gene expression and possible mechanisms underlying observed behaviours of the adhering cells.
2:10 PM		TS3-1-4 Characterisation of Ca- and P-Containing PEO Coatings on Ti Substrates A. Yerokhin (University of Sheffield, United Kingdom); A. Pilkington (University of Sheffeild, United Kingdom); A. Matthews (University of Sheffield, United Kingdom) Plasma electrolytic oxidation (PEO) of Ti is currently attracting major attention for surface engineering of intrabone implants. Enhancements in bioactive properties of PEO titania can be achieved by tailoring surface morphology, controlling anatase to rutile ratio and incorporating appropriate elements (e.g. P and Ca) into the coating material. The account for these routes was taken during development of an advanced PEO process based on application of pulsed reversed current modes. Produced coatings were characterised in terms of thickness, roughness, elemental and phase compositions. Nanoindentation measurements and scratch adhesion tests were performed to evaluate mechanical properties of the surface layers. A series of in vitro assays was carried out to evaluate cell viability, collagen activity and attachment to the substrate. It is shown that uniform and strongly adhered to Ti substrate oxide ceramic coatings with 5 to 30 micron thickness can be obtained using the PEO method developed. The coatings possess high ratio of Ca/P = (1.5..3)/1 which results in formation of bioactive components (e.g. hydroxyapatite and calcium phosphates), in both amorphous and crystalline from, within the titania matrix. The coating stiffness lies between that of Ti substrate and bone material, thus providing graded transition in mechanical properties across the bone implant interface. New coatings possess high biocompatibility and enhanced bioactive properties compared to both untreated Ti and conventional PEO coatings. The versatility of the method is demonstrated by examples of coating deposition on different Ti alloys and components of prosthetic devices of complex shape.
2:30 PM		TS3-1-5 Effects of Sterilization and Heat Treatment on Alumina Coated Surgical Instruments A.C. Ruiz, M. Kavdia (University of Arkansas); S. Kumar (University of South Australia); M.H. Gordon (University of Arkansas); H.H. Abu-Safe (Lebanese American University, Lebanon); S. Davis (Philander smith College) Alumina thin films were deposited on surgical stainless steel scalpel blades to test the sharpness of the coated blades, to investigate the effects of sterilization on both the phase of the film and the adsorption of protein, and to study the thermal stability of the film. The films were deposited using an inverted cylindrical dual magnetron sputtering system. Process parameters such as power, pressure, oxygen partial pressure, and substrate bias were varied to grow the films. Alumina coated samples were sterilized in a steam autoclave for 1-10 cycles, each of 40 minutes. The film phase before and after sterilization was determined by X-ray diffraction. The adhesion of BSA protein was quantified by Fourier transform infrared spectroscopy. Preliminary results indicate that the coated blades adsorbed 50% less protein when compared to the uncoated blades. Coated samples were annealed to temperatures up to 1200°C to study thermal and structural stability. Sharpness of the coated surgical scalpel blades was investigated by pushing the blade into an elastomeric material and measuring the cutting force. Preliminary results indicate that the blades coated with alumina remain sharper for a longer period of time.
2:50 PM		TS3-1-7 Spray-Pyrolyzed Hydroxyapatite Thin-Film Coatings M. Aguilar-Frutis (CICATA-IPN, Mexico); S. Kumar (University of South Australia); C. Falcony (CINVESTAV-IPN, Mexico) Plasma-sprayed hydroxyapatite (HA) coatings have been used on metallic bone implants for about 20 years now, but there are still many issues that continue to be addressed for improving the use of HA coatings for improved implant fixation. One such issue is the deposition of HA thin-film coatings with high purity and crystallinity, primarily aimed at realising cost-effective coatings with improved adhesion and predictable properties. A range of deposition methods such as sputtering, electrodeposition and ion-beam deposition have been employed to achieve this goal, with some success. The work presented in this paper is motivated by the need to deposit cost-effective HA thin-film coatings with high purity and crystallinity. For this, we have employed the technique of spray pyrolysis, a simple thin-film deposition method with low setting-up costs and capable of batch processing at atmospheric pressure air ambient. The spray pyrolysis set-up we have used consists of an ultra sonic generator used for mist production from a spraying solution containing the precursor materials. The mist is transported through a glass tube to the substrate surface which is heated to achieve the pyrolytic chemical reaction. Some preliminary results obtained on the deposition and characterization of HA thin-film coatings deposited by this spray pyrolysis system on 2 mm thick Ti6Al4V sheet substrates will be presented and discussed. A 0.042 M calcium spraying solution was prepared by dissolving calcium acetylacetonate hydrate 99.95% in N,N-Dimethylformamide. Phosphoric acid (H3PO4) was used as source of phosphorous. A 0.27% vol. solution of H3PO4 in deionized water was prepared and supplied simultaneously and in parallel during the deposition. The coatings were deposited for 25 minutes at a substrate temperature of about 500ºC. The chemical composition, surface morphology and structure of the HA coatings were determined by scanning electron microscopy (SEM), X-ray phot oelectron spectroscopy (XPS) and X-ray diffraction (XRD). The high purity of the coatings was revealed by the presence of Ca, P and O as the main constituents, with a Ca/P ratio of about 1.3. Some carbon, inherent to the precursors used, was also detected. The XRD patterns obtained suggested preferred (113) and (321) crystal orientations in the coatings.
3:10 PM		TS3-1-8 The Influence of Electrochemical Parameters on the Microstructures and Bactericidal Abilities of Anodized Titanium Dioxide Nanotube Arrays L.-S. Liu, Y.-J. Chang, J.-W. Lee, H.-P. Chen (Tungnan University, Taiwan) The photocatalytic titanium dioxide has been widely applied in the pollution removal and environmental protection field. Recently, the role of titania is getting more and more important due to its water splitting ability to produce hydrogen. In this work, a pulsed DC power supply was adopted to anodize the pure titanium plate to produce TiO₂ nanotubes. Amplitudes of the negative and positive voltages and time were adjusted to study their influences on the morphologies and dimensions of TiO₂ nanotubes. The anodized titanium plates were further annealed at 450°C for 30 minutes in air. The antibacterial tests of TiO₂ nanotubes with different dimensions were performed to evaluate the bactericidal ability against E. coli. It was found that the amphorous titanium dioxide nanotubes were produced under suitable experimental parameters on the surface of pure titanium plate. The crystalline anatise structure of TiO₂ nanotubes were formed after annealing at 450°C for 30 minutes in air. The length of nanotubes increased with increasing amplitudes of positive voltage. The antibacterial abilities of the annealed TiO₂ nanotubes upon low dose of UV irradiation were enhanced effectively. It is concluded that the anodized TiO₂ nanotube array can be used for photo-induced bacteria killing.
3:30 PM		TS3-1-9 Biocompatibility of Niobium-Based Coatings G. Ramírez, S.E. Rodil, H. Arzate (Universidad Nacional Autónoma de México); J.J. Olaya (Universidad Nacional de Colombia); E. Camps (Instituto Nacional de Investigaciones Nucleares, México); S. Muhl (Universidad Nacional Autónoma de México) Niobium based thin films were deposited on stainless steel substrates to evaluate them as possible biocompatible surfaces that might improve the biocompatibility and extend the life time of stainless steel implants. Niobium nitride and niobium oxide thin films were deposited by reactive unbalanced magnetron sputtering on AISI 316L substrates under standard deposition conditions and without substrate bias or heating. The biocompatibility of the surfaces was evaluated by testing the cellular adhesion, proliferation and the viability of human cementoblasts cells, during different periods of time up to 7 days. Moreover, preliminary studies of the mineralization process were done up to 14 days. The response of the films was compared to the bare substrate and Ti₆Al₄V pieces; the most commonly used implant material for orthopaedic and osteosynthesis applications. The physico-chemical properties of the films were evaluated by different means; X-ray diffraction (XRD), Rutherford Backscattering spectroscopy (RBS), energy dispersive X-ray spectroscopy (EDX) and contact angle measurements. The results of XRD and RBS suggested that the niobium oxide films were amorphous but having the Nb₂O₅ stoichiometry, while the niobium nitride films were crystalline showing a one to one composition and fcc phase. The biological evaluation showed that the biocompatibility of the stainless steel can be improved by any of the two films, but in any case it was better than the Ti₆Al₄V alloy. On the other hand, comparing the two films the NbN seems to be a better surface than the oxide in terms of the adhesion and proliferation of cemetoblasts human cells.
3:50 PM		TS3-1-10 Low-temperature Deposition of Anatase TiO₂ on Medical Grade Polyetheretherketone to Assist Osseous Integration H.-K. Tsou (Feng Chia University, Taichung Veterans General Hospital & Jen-The Junior College of Medicine, Taiwan); P-Y. Hsieh (Feng Chia University, Taiwan); C.-J. Chung (Central Taiwan University of Science and Technology, Taiwan); C.-H. Tang (China Medical University, Taiwan); T.-W. Shyr, J.-L. He (Feng Chia University, Taiwan) Polymeric polyetheretherketone (PEEK) has been widely applied in spinal interbody fusion cages for its chemical inertness and bioinertness. PEEK itself is also free from osteo-induction because of its bioinertness and hydrophobicity. Titanium dioxide (TiO₂), known to exhibit good antimicrobial activity, hydrophilicity and bioactivity, is applied in this study as a thin film formed onto PEEK substrate deposited at low deposition temperature using an arc ion plating (AIP) technique. The microstructure, mechanical properties and osteoblast compatibility of the AIP-TiO₂ deposited PEEK are evaluated to investigate the feasibility of using this technique for faster osseous integration on spinal interbody fusion cages. The experimental results showed that the deposited TiO₂ possesses a dense columnar structure with anatase TiO₂ as the main phase and rutile phase as the minor phase. The pencil hardness of the TiO₂ deposited specimen reached over 9H. The highest rank (5B) was achieved in an adhesion tape test. This firm and compact TiO₂ film corresponds to a critical load of 14.5 N as measured by the scratch test, with the coating experiencing a cohesive failure mode; an indication of strong film adhesion force. High corrosion potential with very low corrosion current was detected both in 3.5 wt.% NaCl electrolyte and simulated body fluid (SBF), indicating the electro-chemical inertness of the TiO₂ coating prepared using the AIP technique. The TiO₂ coating presented better osteoblast compatibility than the bare PEEK material in terms of cell adhesion, cell proliferation and alkaline phosphatase (ALP) activity in an osteoblast culture. This brings an ideal AIP-TiO₂ coating for use as a supplement for faster and better osseous integration on PEEK cages.
4:10 PM		TS3-1-11 Investigation of Microstructure and Properties of Plasma-Sprayed HAp-TiO₂ graded Coatings A. Iwaniak, M. Sozanska (The Silesian University of Technology, Poland) The article presents results of microstructural investigation and properties characterization of HAp-TiO₂coatings on Ti6Al4V alloy. Hydroxyapatite and TiO₂ coatings were deposited on titanium alloy substrates by atmospheric plasma spraying (APS) using of commercial powders. The layers hydroxyapatite/TiO₂ bond coat consists different percent amount hydroxyapatite and TiO₂. The microstructural characterization of the Hap-TiO₂ coatings before and after heat treatment was conducted by using scanning electron microscopy (SEM), electron probe microanalyser, X-ray diffractometer (XRD) and transmission electron microscopy (TEM). The as-sprayed coating consists mainly of crystalline Hap, rutile TiO₂ and amorphous Ca-P phase. The results of the preliminary investigations were used to optimize the spraying conditions for the analyzed functionally graded hydroxyapatite depositions and, accordingly, the final graded coatings was obtained and cha racterized.