Study on titanium-hydroxyapatite composites and development of an innovative cladding method for hard tissue implant applications

Titanium/hydroxyapatite (Ti/HA) composites have demonstrated promising perspective to be used as hard tissue implants. However, the conventional high concentration of HA addition significantly compromises the mechanical properties. This thesis conducted a series of studies on Ti/HA composites with low HA additions (≤20 vol.%) and developed an innovative cladding method to broaden their applications.;Next, the in vitro bioactivity of the fabricated Ti/HA composites was evaluated in a simulated body fluid (SEW). After immersion in the SBF, the composite could induce the nucleation and growth of the carbonated apatite even though the HA concentration was low. The Ti-OH groups by hydration, the presence of Ca on the surface, and the dissolution of CaO were the main factors contributing to the bioactivity of the composites. The results substantiated that the Ti/HA composites with low HA additions were bioactive and had the potential to be used for hard-tissue replacement.;Furthermore, a novel cladding method was developed to join Ti/HA and Ti/Fluorapatite (Ti/FA) composites to the Ti6A14V substrate for load-bearing applications. Applying a silver interlayer and an external pressure during sintering was proved to be critical for achieving the defect-free interface between the composite and the substrate. The fabricated materials demonstrated in vitro bioactivity in the SBF. Favorable ions, such as Ag + and F-, were detected in the fluid, which could enhance the functionalities of the materials. This study indicated that the cladding method could be adopted to tailor the biological properties of the material for different applications.;Keywords: Titanium, hydroxyapatite, fluorapatite, composite, in vitro bioactivity, simulated body fluid, cladding.;Firstly, the sintering behaviours of Ti/HA composites with various HA additions and the interactions between Ti and HA were investigated. The HA addition markedly inhibited the densification of the materials. The presence of Ti accelerated the dehydroxylation and decomposition of HA which could occur at a temperature as low as 800°C. Ca4P2O 9 and CaO were detected as the dominant decomposition products of HA in the Ti/HA system at low temperatures, while CaO was the only detected product at high temperature (1200°C). At the same time, oxidation of Ti occurred during sintering.