Key Engineering Materials Vols. 396-398

Abstract: Among surface modifications commercially available for dental implants, the incorporation of bioceramic coatings is one of the most popular. However, concerns regarding the effectiveness of the bond between the metallic surface and the coating have led to the development of thin-film Ca- and P- based bioceramic coatings. The purpose of this study was to evaluate the early bone response to a thin ion bean deposited (Test) bioceramic implant surface compared to an alumina-blasted/acid-etched (Control) surface in a canine model. Results showed that although no difference in bone-to-implant (BIC) could be noted between the two different surfaces, more organized bone architecture was present around the Test implants in 4 weeks. Based on this observation, the incorporation of a thin- film bioceramic coating positively influenced bone healing around dental implants at early times.

Abstract: Many attempts had been made to improve the durability of artificial joint replacement and other orthopaedic implants by approaching the mechanical properties of bone and artificial material. The most joint prostheses used today are manufactured of metal alloys based on cobalt, chromium or titanium. The mechanical stiffness of these materials is much higher than that of natural bone resulting in adverse effects such as local overloading on one hand or stress shielding phenomena with the lack of adequate mechanical load on the other. Both mechanisms contribute to earl loosening and failure of implants. Polymer materials may deliver mechanical properties very similar to bone and their mechanical behaviour may be modified in a wide range during the process of manufacturing. First attempts to lower the stiffness of the implant material and to gain the stiffness range of natural bone were made in the seventies by R. Matthys with his concept of “isoelastic hip prosthesis”. In this prosthesis the femoral stem was manufactured of polyacetal, a thermoplastic polymer with very good biocompatibility and elastic properties which are much nearer to bone than common metal alloys. While the prosthesis showed good results during the mechanical testing the clinical use in vivo became a disaster. Shortly after implantation polyacetal was degraded in the body and broke down under the immense loading of the human hip joint. Later attempts to use polymer materials alone for load bearing implants also failed in clinical practice over a long time because the mechanical interlocking between bone and implant was not sufficient for the biological demand. To make the outstanding properties of polymer materials useable for load bearing implants they are backed with metal alloys (as polyethylene for hip joint cups) until the presence. Only recent developments of polymer science succeeded in the use of polymers for loaded implants. One of the most interesting materials seems to be the polyetheretherketone (PEEK) which is successfully used for spinal fusion cages [2] and computerdesigned individual implants for defect reconstruction in the skull [4] meanwhile. A pre-clinical study of a new anatomically shaped flexible acetabular cup reported satisfactory results recently [3].

Abstract: In this work, we explore the deposition of single-phase and uniform HA coatings on a crystalline silicon surface of microelectronic quality. The used methodology includes an NaOH treatment to produce the silanization of Si surface and a modified biomimetic technique, using sodium silicate solution (SS) as nucleant agent, for apatite-based coating formation. The sodium silicate solution (SS) demonstrated to be effective for the calcium phosphate layer formation, but the treatment can reduce the induction to obtain a uniform surface coating of HA. This suggests that, among the factors that determine nucleation of calcium phosphate on silicon, surface electrical charge could play a key role.

Abstract: It has been shown that titanium metal subjected to NaOH and heat treatments spontaneously forms a bonelike apatite on its surface in the living body and bonds to living bone. However, its apatite-forming ability was liable to decrease when the treated titanium metal was stored in humid environment. In the present study, the NaOH-treated titanium metal was soaked in a CaCl2 solution at 40°C for 24h, heat-treated at 600°C for 1h, and then soaked in ultrapure water at 80°C for 24h. Calcium titanate was formed on the surface of the titanium metal 1µm in thickness by these treatments. The resultant titanium metal showed high scratch resistance and high apatite-forming ability in a simulated body fluid. This high apatite-forming ability was maintained even after the titanium metal was kept in 95% relative humidity at 80°C for 1 week.

Abstract: Hydroxyapatite and silicon-substituted hydroxyapatite powers were prepared in-house through a wet precipitation method and then vacuum plasma sprayed onto Ti-6Al-4V discs. Two plasma gun input powers were employed, 37 kW and 40 kW. All coatings were nearly phase pure, except small traces of impurities (TTCP, -TCP and CaO). Coatings prepared under the lower plasma gun input power had lower crystallinity. In vitro studies showed that human osteoblast-like cells attached and spread very well on all coated discs. Among the four kinds of discs, SiHAC37 was the most supportive to cell growth.

Abstract: In this study, the influence of electrolytic composition and time deposition parameters on the quality of titanium oxide coating was evaluated. The commercial Ti discs were anodized by micro-arc oxidation (MAO) process using calcium acetate monohydrate 0.5M (CaAc) and a mixture of calcium acetate monohydrate 0.5M and sodium beta-glycerophosphate 0.02M (CaAc + BGF) aqueous solutions. MAO was carried out by applying pulsed DC voltage of 150 V at different processing time (05, 15, 30, 45 and 60 seconds). The films were characterized by SEM, EDS, surface profilometer and XRD. Additionally, osteoblasts culture was carried out in order to verify the cytocompatibility of the anodized surfaces. The results showed the formation a well controlled homogenous microporous structures with irregular shapes for both electrolytes. Presence of Ca and P on the surface was found for films produced with CaAc + BGF electrolyte. Also, the adhesion, spreading, proliferation, and differentiation of osteoblast cells were very similar.

Abstract: In a previous study, we have reported that sodium removal by dilute hydrochloric acid (HCl) converted the sodium titanate layer on the surface of an alkali-treated porous titanium into titania with a specific structure that has better bioactivity than sodium titanate. We have shown that a porous titanium with this treatment have good osteoinductivity in soft tissue of canines. In the present study, we investigated the effect of this treatment on the osteoconductive abilities of porous bioactive titanium implant in the long term. Three types of surface treatments were applied: (a) no treatment , (b) alkali, hot water, and heat treatment ( conventional treatment: W-AH treatment), and (c) alkali, dilute HCl, hot water, and heat treatment (Na-free treatment: HCl-AH treatment). We then examined the osteoconductivity of the materials implanted in the femoral condyles of Japanese white rabbits at 6, 12, 26, and 52 weeks. The results showed that the bone ingrowth in HCl-AH porous bioactive titanium was significantly higher than in W-AH porous bioactive titanium at 52 weeks. Therefore, sodium removal has a positive effect on the osteoconductivity of the porous bioactive titanium implant in the long term.

Abstract: Implant failure due to aseptic loosening is a major complication in total hip arthroplasty. Different implant coatings aim to reduce the risk of implant loosening by anti-infectious, bio-active or wear resistant approaches. The mechanical properties, especially bonding strength and wear resistance, of a Cu-TiO2, CaP and TiN coating were investigated in this study. A scratch test and a standard adhesive test were used to determine the bonding strength of the coatings. To analyse the wear resistance a modified special testing machine was used to evaluate wear with PU-foam and PMMA as counterparts. The investigations showed that all coatings have greater bonding strengths than the minimum required 22 N/mm2 for medical implant coatings. Significant differences in total wear were determined during the wear tests. With the exception of the CaP no removal of the coatings was detected.

Abstract: Surface structural change of titanium metal with NaOH and heat treatments and the subsequent soaking in a simulated body fluid (SBF) was investigated by observing cross section of its surface layer by scanning electron microscope. A layer of lathlike phase of sodium hydrogen titanate was formed on the surface of the titanium metal 1 µm in thickness by the NaOH treatment. This was transformed into a layer of lathlike form a little densified of sodium titanate and rutile by the subsequent heat treatment. In SBF, apatite started to precipitate in the interior of the surface lathlike layer, filled the interspaces of the lathlike phases and grew over the surface. This integration of the apatite with the surface lathlike layer might be responsible for the strong bonding of the titanium metal to the living bone.

Abstract: In this study we report on the microstructure and its mechanical behavior of a Ca-P coating produced on bioactive titanium by immersion in a simplified simulated body fluid (S-SBF). The coating was probed by nanoindentation in several point times up to the formation of octacalcium phosphate (OCP). Amorphous calcium phosphate, formed after 1h of immersion in SSBF, presented the highest values of hardness (H) and elastic modulus (E). Nucleation of OCP was observed after 2-2,5h of immersion in S-SBF. From this stage on, lower values of H and E were obtained, probably due to the low dense structure of the coating.