Deposition of HA-TiO2 by plasma spray on β-phase Ti-35Nb-7Ta-5Zr alloy for hip stem: Characterization, mechanical properties, corrosion, and invitro bioactivity

This research work presents the deposition of titanium oxide (TiO2) reinforced hydroxyapatite (HA) on Ti-35Nb7Ta-5Zr alloy by plasma spray deposition technique for Hip-stem application. The effect of TiO2 reinforcement (15 and 30 wt%) in HA has been studied on coatings morphology, microstructure, mechanical properties, corrosion resistance, and in-vitro bioactivity was investigated. The microstructure, elemental composition, and phase composition were characterized by FE-SEM, EDS, and XRD. The morphology analysis showed that of HA-coating contains micro-cracks and splats like structure with large globules. The reinforcement of TiO2 in HA improved the microstructure, prevents the formation of micro-cracks, and formed a dense structure. The crosssection morphology shows that HA-15%TiO2 (HA-T-x) and HA-30%TiO2 (HA-T-y) coatings (thickness 185-200 mu m) were mechanically bonded with the substrate as compared HA-coatings, that helps in enhancing implant stability. Results also show that microhardness and adhesion strength of HA/TiO2 coatings improved with the reinforcement of TiO2 and HA-30%TiO2 possessed high micro-hardness and adhesion strength (1.35 GPa and 32.5 MPa) in comparison with HA-coating (0.63 GPa and 18.5 MPa). The electron dispersive spectroscopy (EDS) analysis and X-ray diffraction analysis (XRD) results show that HA-TiO2 coatings contain HA and TiO2 phases that prevent the formation of amorphous contents. In contrast, HA-coating contains amorphous content (CaO, beta-TCP, and TTCP). The HA-TiO2 coatings exhibit excellent corrosion resistance as compared to HA-coating because of the presence of TiO2 lamellar structure in the HA matrix that acted as a barrier to corrosion and improves the corrosion resistance. The TiO2 reinforcement in HA/TiO2 coating not only increase the corrosion resistance but also help in promoting chemical integration of MG-63 osteoblastic cellular structure through the formation of apatite on the surface of the implant. Furthermore, the in-vitro bioactivity analysis results showed that Mg-63 osteoblastic cells have excellent adhesion and growth on the HA-30%TiO2 coated substrates.