Key Engineering Materials Vols. 330-332

Abstract: Vacuum plasma sprayed (VPS) Ti coatings were deposited and their surface modification processes were performed by NaOH solution treatment and alkali-heat-calcification respectively. The simulated body fluid test indicated that apatite was formed on the surfaces of Ti coatings. A net-like structure was observed on the surfaces of Ti coatings treated by alkali-heat-calcification, whose bioactivity is much better than that treated by NaOH aqueous solution simply.

Abstract: The in-vitro bioactivity of SiC growing using the innovative hybrid laser-magnetron deposition technique was investigated. The biological response has been analysed after being immersed in a human blood plasma solution for 10 days. Surface analysis by SEM microscopy shows clearly an adsorption process after immersion. The products formed are mainly attributed to a rich-calcium phosphate and silica-complexes layers. Citotoxicity test shows a normal phenotype of fibroblast cell culture on SiC and MTT assay indicates an increased viability of cells around 15% after only one day of immersion. Results obtained are supported by FTIR analysis. Strong changes in the absorbance of bands after immersion are observed, which indicates a strong bioactivity of SiC.

Abstract: In this work, collagen type I was covalently grafted on the surface of plasma sprayed titania coatings to improve their biocompatibility. The plasma sprayed titania coatings were pretreated by sodium hydroxide to induce the formation of hydroxyl groups which can covalently graft collagen, rendering the collagen having good stability. The dependence of collagen grafting on the sodium hydroxide treatment conditions (concentration, time and temperature) was investigated by measuring the amount of collagen grafted on the titania surface. The biocompatibility of the titania coatings with grafted collagen was evaluated by in vitro cell culture. The results showed that the amount of collagen grafted on the titania coatings increased with the concentration of the sodium hydroxide and the treating temperature, while that on the coating is slightly dependent on the treatment time in sodium hydroxide. In vitro cell culture test proved the positive effects of collagen on the biocompatibility of the plasma sprayed titania coating.

Abstract: Calcium phosphates coatings were deposited onto titanium discs via en electrodeposition method. Discs were blasted with calcium phosphate particles and etched in a mixture of sulfuric and fluoric acids. Temperatures from 25 to 80°C and current densities from 8 to 120 mA/ cm2 were used. Deposition times tested were between 10 and 120 min. The electrolyte consisted of a super saturated solution stirred at 250 rpm. The amount of magnesium (Mg2+) and carbonate (HCO3-) ions was varied from 0 to 1 mM. Coatings increased in thickness by increasing deposition time. The different amounts of Mg2+ and HCO3- affected the homogeneity and morphology of the coatings. Main factors affecting the deposition were temperature of electrolyte and current density.

Abstract: Although compositional gradients could be manufactured for the functionally graded coating that was showed to improve bonding strength between the coating and the substrate, the biological efficacy of the graded coatings remained unclear. In this study, a functionally graded nanophase hydroxyapatite/bioglass (n-HA/bioglass) coating was prepared on a titanium (Ti) substrate for evaluating peri-implant osteogenesis in a canine model. The bone apposition and osteointegration of n-HA/bioglass coating were investigated at the interface compared with plasma spraying HA (PS-HA) coating. The results showed that the coating degraded gradually over time but not as fast as PS-HA coating did, and that more active bone apposition appeared on the n-HA/bioglass coating. The in vivo study indicated that an early osteogenesis and osteointegration at the interface could be stimulated by the use of n-HA/bioglass coating in biological environment.

Abstract: In this work, nonstoicheometric titanium oxide film on silicon matrix was prepared by unbalanced reactive pulsed magnetron sputtering /hydrogen plasma reduction method. The film chemical composition was analyzed by X-ray diffraction and X-ray photoelectron spectroscopy (XPS). The XRD patterns of the prepared films showed that titanium oxide films possess the single phase rutile structure . the XPS spectra of the film displayed that the valence state of Ti is Ti4+, Ti3+ and Ti2+ respectively and the films were nonstoichiomeric Ti-O film. The evidence showed that isolated oxygen exist in films. Ti/O ratio of Ti-O film from the XPS data vary with depth under different reduction temperature and time. And it corresponded with platelet adhesion tests of Ti-O film in vitro. Antithrombotic property of reduced titanium oxide thin films was examined by platelet adhesion tests. The results showed that the Ti-O films with lower non-stoicheometrical extent posses the better anticoagulation property than stoichiomeric TiO2 film and the Ti-O films with higher non-stoicheometrical extent. Hence hydrogen introducing is an effective way to improve the bloodcompatibility of titanium oxide film.

Abstract: Hydroxyapatite (HA) coated total hip joint device has caused concerns of generating wear particles after long-term implantation. We designed a pin-on-disk (POD) test to examine the morphological changes and wear particle generation of plasma sprayed HA coating in vitro. HA coatings were immersed in supplemented α-calf bovine serum for 48 hours. Serum soaked HA coating exhibited significant amount of weight loss due to dissolution of amorphous calcium phosphate (ACP). POD test demonstrated the serum soaked HA coatings presented many micronsized particles on the surface while the as-received HA coatings maintained good integrity. The generation of wear particles of the serum soaked HA coatings is related to the reduction of the cohesion/adhesion of HA coatings due to the preferential dissolution of ACP.

Abstract: Titania (TiO2) thin films were fabricated on titanium (Ti) substrates at low temperatures by electron cyclotron resonance (ECR) plasma oxidation, and the relationship among the oxidization conditions, crystal structure and osteoconductive property was investigated. Amorphous TiO2 films were obtained below 300°C and crystallized rutile-type TiO2 films were obtained above 400°C. The XRD peak intensity of rutile TiO2 increased with increasing oxidation temperature. Mixtures of octacalcium phosphate (OCP) and Dicalcium phosphate dihydrate (DCPD) peaks were observed after calcification. The intensity of the OCP and DCPD peaks after calcification increased with increasing oxidation temperature. The ECR plasma was significantly effective to prepare crystallized TiO2 films at low temperatures.

Abstract: To accelerate the bone growth around a metallic implant and to achieve the mechanical characteristics needed for biomedical applications, a HA/Ti composite coating was produced on NiTi alloy substrate by laser cladding. The chemical compositions, microstructures and surface morphology of the cladded layer were analyzed using energy dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), and X-ray diffractometry (XRD). The experimental results showed that an excellent metallurgical bonding between the coating and the substrate was obtained. Owing to decomposition of HA under irradiation of high power laser, the microstructures in bioceramics coating were mainly composed of CaO, CaTiO3, Ti4P3, and HA phases. In vitro experimental result showed that HA/Ti composite coating made the bioactivity of NiTi alloy improve remarkably, which would promote the bone growth and could restrain Ni ion releasing from NiTi alloy.