ICMCTF2013 Session DP: Syposium D Poster Session

Whenever a foreign material comes in contact with a biological media a complex cascade of events is triggered. After the adsorption of water molecules and hydrated ions, the adsorption of proteins from the biological media onto the material surface occurs. This leads to the formation of an adsorbed protein layer that directs the next coming cell – material interactions. Consequently, the protein adsorption studies constitute an excellent model to study the interaction between biological media and foreign materials and to gain a deeper understanding of the influence of the material physicochemical properties in this interaction.

In the last years, the influence of the physicochemical properties of foreign materials on the biological response has been widely studied and some surface properties such as the hydrophobicity and roughness are well known to affect the materials-biological media interaction. However, the influence of the atomic ordering has been less explored. In the present study, zirconium oxide, a widely known biocompatible material was chosen as the model material to study the influence of surface atomic ordering on protein adsorption; Fibrinogen (Fbg) was chosen as the model protein. Quasi-amorphous (q-a) and polycrystalline (p-c) zirconium oxide thin films were deposited on Si(100) substrates by Reactive Magnetron Sputtering. The atomic ordering, wettability, surface energy, roughness, optical properties and chemical composition of the films were characterized. The films were immersed in BSA solution and the protein adsorption was studied in-situ using dynamic and spectroscopic ellipsometry.

The results showed that the film roughness, as well as the water contact angle, increased with the atomic ordering of the film. A slightly higher Fbg adsorption rate was observed on the p-c ZrO₂ film compared to the adsorption rate observed for the quasi-amorphous film. The differences observed in the Fbg adsorption on the two films might be related to the changes in the films roughness/wettability induced by the changes in the surface atomic ordering.

A widely utilized spinal implant materials, polyetheretherketone (PEEK), with its bio-inert and hydrophobic surface was suggested to proceed surface modifications for seeking better biocompatible performance. On the other hand, hydroxyapatite (HAp) exhibits excellent osteoconductive property, has been also regarded as a promising candidate for biomedical applications. The present study employed an arc ion plating (AIP) technique to respectively deposit rutile-rich titanium dioxide (R-TiO₂) and anatase-rich titanium dioxide (A-TiO₂) interlayers onto PEEK substrates, which were then immersed in simulated body fluid (SBF) for studying HAp layer growth. The microstructure observation and osteocompatible tests are carried out to evaluate the effects of HAp growth and osteoblast adhesion ability on adoption of TiO₂ interlayer.

Experimental results showed that HAp growth can be effectively enhanced by adoption of TiO₂ interlayer in SBF environment, with the crystallinity and film thickness of grown HAp layer proportional to immersion time. It was also worth to note that the R-TiO₂/PEEK specimen exhibit superior ability to induce HAp formation, due most likely to negatively charged –OH⁻ groups on R-TiO₂ coating surface at early stage. Furthermore, the osteocompatibility of bare PEEK substrate and interlayered specimen in terms of cell adhesion significantly correlated positively with the extent of HAp layer formation.

This study was to investigate the corrosion resistance of Ni-free Zr_62.5Cu_22.5Fe₅Al₁₀ bulk metallic glass (BMG) alloy, before and after nitrogen plasma immersion ion implantation (N-PIII), for biomedical application. The corrosion resistance, in terms of potentiodynamic polarization curve and metal ions release measurements, was evaluated in artificial saliva and simulated blood plasma solutions. Commercial biomedical pure Ti was used as the reference group for comparison. Results showed that the N-PIII-treated BMG alloy had lower corrosion rate and higher corrosion potential than the untreated BMG and Ti. The N-PIII treatment significantly improved the pitting corrosion resistance and decreased the metal ions release of BMG alloy. In terms of corrosion resistance, the Ni-free Zr_62.5Cu_22.5Fe₅Al₁₀ BMG alloy has potential for biomedical applications; N-PIII treatment further improves the corrosion resistance of BMG alloy.

Titanium and its alloys are one of the most used materials in many industries such as aerospace, military and biomedical due in part to a combination of properties including low weight and good biocompatibility. One of the low points of this material is the poor wear resistance particularly in sliding conditions. Many PVD coatings are intended to improve the wear resistance by modifying the surface properties of a big variety of substrates while retaining or enhancing existing properties. In this work, ceramic TiAlN/TiB₂ coatings were deposited by DC/RF magnetron sputtering under a selection of parameters. The mechanical properties were measured by nanoindentation techniques, while the structural properties were explored through XRD experiments. The thickness of these coatings and the after deposition roughness were measured by means of profilometry. Tribocorrosion behaviour was evaluated from open circuit potential (OCP) during reciprocating sliding in combined tests using SBF as the electrolyte at 37 °C. Results indicate that hardness values reached more than 20 GPa in all cases, while the thickness was in the range of 3-4 μm. The structural analysis revealed the presence of TiAlN and boron-containing phases. Finally, tribocorrosion results of coated samples showed a considerable change towards positive values in the E_corr and slightly lower values were registered in the current density I_corr during sliding conditions at 1 and 2N.

The tribocorrosion phenomenon is present in biomedical alloys used in artificial implants to replace natural joints. This damage limit the service life of such implants, the hard coatings can improve the wear and corrosion resistance. The TiAlPtN coatings were deposited on CoCrMo alloys by magnetron sputtering. The structure of coatings was studied by means of XRD and the composition by RBS technique. The tribocorrosion behavior CoCrMo alloys alone and coated with TiAlPtN was studied in simulated body fluid. The tribocorrosion was performed using a ball on plate reciprocating tribometer, the test was conducted in a simulated body fluid at 37 °C of temperature. The loads used were 0.5 N and 1N, the oscillating frequencies was 1Hz. The corrosion and tribocorrosion were studied using open circuit potential (OCP), potentiodynamic polarization, cyclic polarization and potentiostatic polarization measurements. The potentiodynamic polarization was used to estimate the change in the corrosion rate due to wear and the potensiostatic polarization in the passive region to measure the change in the wear rate due to corrosion. The surface topography and worn surface were studied by means of profilometry. The Pt content in TiAlN films was about 0.5 at. %, the coatings improve the corrosion and tribocorrosion resistance of CoCrMo alloys.

Diamond like carbon (DLC) coatings have been proven to be an excellent choice for wear reduction in many technical applications. However, for successful adaption to the MedTech field, layer performance, stability and adhesion in realistic physiological setups are very important and not consistently investigated. Simulator testing as well as corrosion tests are of great importance to verify the long term stability of such a DLC coated articulating implants in the human body. Commonly one million cycles of simulator testing correspond to 1 year of articulation in the human body. Diamond like carbon coatings were deposited on CoCrMo biomedical implant alloy using a plasma-activated chemical vapor deposition (PACVD) process. As an adhesion promoting interlayer tantalum films were deposited using magnetron sputtering.

It is shown that metal-on-metal (MoM) pairs perform well up to 5 million loading cycles, after which they start to generate wear volumes in excess of 20 times those of DLC-coated implants. This is attributed to the slight roughening observed on unprotected metal surfaces as usually also observed in-vivo. The DLC on DLC inlay pairs show comparable low volume losses throughout the full testing cycle (up to 101 million cycles over a period of three years and two month). To our knowledge this is the first time a simulator test of a DLC-coated articulating implant running for more than 100 million (corresponding to over 100 years of articulation in-vivo) cycles is presented.

Within this time these implants were characterized by high wear resistance, low friction coefficients, high corrosion resistance and low defect growth. These results were obtained by means of optical microscopy, SEM/EDX, FIB cross section and profilometry. The coatings were further analyzed using XRD and XPS.

A bioceramic TiO2 coating with Hydroxyapatite (HA) and Silver (Ag) deposited on Ti6Al4V alloy screws was produced by using a combination of electrophoretic deposition coupled plasma electrolytic oxidation (PEO) and anodizing processes. The coatings revealed a relatively rough and porous surface which may potentially promote a higher anchorage as well as more favorable osteointegration properties to the bones. In this paper, an insertion torque (IT) analysis on low (10 pcf, pounds per cubic feet), middle (15 pcf), and high (20 pcf) density sawbones and real pig bones were carried out and compared with the uncoated screws. Higher insertion torques and final seating torques were obtained in the coated screws which may result less micromovement after implantation and thus lower the risk of implant failure. Surface morphological evaluation before and after insertion and removal by SEM and EDS were further performed. The coatings remained adhered to the substrates. No loss of HA and Ag particles from the coating was observed. These results qualitatively implied a good bonding strength between oxide coating and Ti alloy substrate.

Metallic archwires have been successfully employed in orthodontics for the last decades. Such commercial archwires are made of either stainless steel (CrNi) or NiTi alloys. Both epoxy resin and polytetrafluoroethylyene (Teflon^®) thick coatings are commonly used to cover orthodontic archwires exclusively for esthetic purposes. However, some papers have reported the presence of coatings failures in clinical use. Even so, a few works have been published concerning their coating-substrate adhesion, as well as their mechanical and tribological properties. In the present study, five commercialized coated esthetic orthodontic archwires from different manufacturers were studied, as follows: Orthometric (China), Ortho Organizers (USA), TP Orthodontics (USA), Trianeiro (Brazil), and Tecnidente (Brazil). Coatings hardness and elastic moduli were assessed by instrumented indentation tests. For a 2.0 mN load, they presented hardness in the 170 – 250 MPa range, while their elastic moduli varied from 5.5 to 7.7 GPa. Scratch resistance of coatings and their substrates were evaluated by scratch tests. A total of 5 tests were performed on each sample by the ramping load method with loads from 0 to 500 mN, 500 µm scratch length, 50 µm/s scratch velocity, and a diamond Berkovich-geometry tip displaced in the knife-face position. All tests were carried out in air at room temperature. For the tested coatings, the maximum penetration depths of about 12.0 µm were achieved; thereby, the substrates were not reached once the coatings are as thick as 20.0 µm. Despite having elastic recoveries of about 70 - 90%, different failure features could be observed along the scratches by scanning electron microscopy. In some cases, delamination, crack propagation and debris generation were observed. In fact, such failures must be avoided for clinical use. Coating detachment due to poor substrate-film adhesion was not evident. The coatings coefficient of friction (COF) increased linearly up to 0.3 (~ 50 mN load), and then, leveled off in the 0.34 – 0.40 range for higher loads. The COF of the CrNi and NiTi substrates had a different behavior. They increased during all the tests while the loads were ramped. In the beginning, the COF of the substrates were lower than those obtained for coatings for loads up to 250 mN. For the higher loads, the COF increased until 0.45. The coated archwires most resistant to scratch were those that presented little plastic (permanent) deformation associated with minor damaging features.