The osteoconductivity is the most desirable characteristic to achieve early fixation of the cementless-type artificial joints with bone. Apatite deposition on the surface of materials can induce the osteoconductivity in bony defect. In previous studies, various surface treatments have been proposed to provide titanium-based artificial joints with the osteoconductivity. The most popular surface treatment for commercial artificial joints is plasma-spray coating with apatite. Although the technique has been widely used for commercial artificial joints in the world, it remains some disadvantages attributed to high temperature during the process, such as fracture at the interface between metal and apatite, changes in the composition, crystallinity and structure of plasma-sprayed apatite. The chemical surface treatment with NaOH and H2O2 solution to provide spontaneous apatite-forming ability in the body could overcome the problems of plasma-spray process, since the treatments could be expected to not only continually express the apatite-forming ability in the body but also deposit the bone-like apatite having the similar crystal structure, crystallinity and composition of bone apatite. Therefore, surface treatments provided the spontaneous apatite-forming ability would be effective for titanium-based artificial joints with osteoconductivity.

Recently, our research group developed the extremely simple technique for providing the spontaneous apatite-forming ability to titanium by both spatial design and thermal oxidation, denoted as “GRAPE technology”. Pure titanium with machined micro-groove of less than 800 μm in depth and 1000 μm in width and thermally oxidized at 400°C in air induced apatite deposition in the internal space of micro-grooves during exposure to simulated body fluid. In this study, the application possibility of GRAPE technology was examined by using Ti-6Al-4V and Ti-15Zr-4Ta-4Nb. Apatite formed on the thermally oxidized Ti-15Zr-4Ta-4Nb at 500 and 600°C with micro-groove 500 μm wide and depth in the simulated body fluid for 7 days. In contrast, no apatite formation was observed on the thermally oxidized Ti-6Al-4V at 400, 500 and 600°C with micro-groove 500 μm wide and depth in the simulated body fluid for 7 days. Okazaki et al. reported that Ti-15Zr-4Ta-4Nb shows higher corrosion resistance, mechanical properties and cytocompatibility than Ti-6Al-4V. Hence, it is expected that the Ti-15Zr-4Ta-4Nb with GRAPE technology could be innovative cement-less artificial joints to achieve early fixation through its osteoconductivity and excellent performances.