Preparation of brookite-type titanium dioxide particle layer on titanium surfaces via hydrothermal treatment and evaluation of in vitro apatite-forming ability

In this study, we prepared a brookite-type titanium dioxide particle layer on the surface of titanium substrates via hydrothermal treatment in aqueous urea solutions containing sodium chloride (NaCl) and examined its in vitro apatite-forming ability. Increasing the urea concentration suppressed the formation of anatase-type titanium dioxide on the titanium substrate, forming a particle layer composed of pure brookite-type titanium dioxide. The size and packing density of brookite-type titanium dioxide particles formed on the titanium substrate increased with the NaCl concentration in a 7.0 mol·dm−3 urea solution. When titanium substrates hydrothermally treated in aqueous solutions of 7.0 mol·dm−3 urea and 2.0 mol·dm−3 NaCl were soaked in a simulated body fluid for various periods up to 7 d, the substrate surface was densely covered with hemispherical apatite particles (5.3 µm in diameter) within 3 d, indicating that the brookite-type titanium dioxide particle layer had an excellent apatite-forming ability comparable to that of the anatase-type titanium dioxide particle layer.