Study On Controlled Hydrothermal Synthesis Of Hydroxyapatite Nanocomposite Coating On Titanium Substrate

Titanium (Ti) and its alloy have been extensively applied to orthopedic and dental implants due to its excellent physical and mechanical properties, however, the bioinert nature restrain its further uses, surface modification should be implemented to enhance its osteogenic activity; hydroxyapatite (Ca10(P04)6(OH)2, HAP) regards as a calcium phosphate based biological ceramic, exhibiting high performance of bioactivity and biocompatibility, with the composition and structure both are similar to the natural bone, which is recognized as the most eligible material could be potentially integrated with the advantages of titanium to form a composite coating for versatile usages such as medical implant.Recently, with the development of biomimetic technique due to the excellent natural adhesive effect of polydopamine was inspired by mussels, and hydrothermal method is always used to fabricate coatings. Based on that, this paper aims to synthesize hydroxyapatite coating on titanium substrate by biomimetic-hydrothermal method and template-hydrothermal method respectively, the main contents are as follow:(1) Biomimetic-hydrothermal method:Firstly, a hydroxyapatite seeded layer was constructed on the surface of titanium substrate by means of biomimetic mineralization, which further facilitated the hydrothermal deposition. With characterizations of X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and so on, indicated that biomimetic mineralization was applied to provide the seeded layer, which was prerequisite and facilitated the subsequent hydrothermal growth, while hydrothermal process promoted the nucleation and crystal growth; titanium substrate retained its pure phase and the unique high crystalline Ca/P phase was HAP with the similar ratio of Ca/P to the natural style and c-axis oriented; the morphology of which mostly expressed its idealized crystal form of hexagonal prism and the structure was supposed to be multi-level assembled by porous Ti/polydopamine/HAP seed/nano prism-like HAP respectively; while the nanocomposite coating was observed homogeneous, crack-free and adherent with uniform thickness, which could be considered as a good quality biomaterial for versatile usages; throughout all synthesis processes were simply chemical-treated under a moderate condition while the highest temperature would not exceed 180℃, furthermore, the synthesis parameters were optimized:Piranha solution was used to activated the titanium substrate; biomimetic period was 2d; hydrothermal chelating reagent was EDTA; pH was 10; hydrothermal temperature was 180℃ and hydrothermal time was 24h.(2) Templated-hydrothermal method:Using L-dopamine as hydrothermal template one-step hydrothermal synthesis of hydroxyapatite coating on titanium substrate. By means of the characterization methods above, proved that the addition of trace amounts of L-dopamine played a certain role in the formation and morphology of hydroxyapatite, and was beneficial to the hydrothermal synthesis of hydroxyapatite coating on titanium substrate. Carbonated hydroxyapatite (CHAP) which is more similar to the natural bone tissue component was achieved under the presence of L-dopamine; while its morphology shown nano plate hierarchical structure, recognized as the unique microstructure as the hydroxyapatite shown under biological environment. The optimized synthesis parameters were:Piranha solution was used to activated the titanium substrate; the concentration of L-dopamine as templated reagent was 5mM; the concentration of urea as precipitator was 0.5M; hydrothermal temperature was 180℃ and hydrothermal time was 24h.