Hydrothermal calcification of bioglass film in CaHPO₄ solutions

Bioglass film was sol-gel coated on titanium substrate, followed by hydrothermal treatment in water, 2.5 mM and 10 mM CaHPO₄ solutions, respectively. X-ray diffraction analysis reveals amorphous nature of the gel powder sintered at 610 °C, but small diffraction peaks of Ca₃SiO₅ are also observed. The absorption bands of Si-O-Si bonds, PO₄ and OH groups are present, while those of NO₃ groups are absent in Fourier transform infrared spectrum of the sintered gel powder. Scanning electron microscopy observation shows that the surface of the sintered bioglass film is porous (pore size ∼200 nm), and nanocrystallites (width ∼20 nm, length ∼200 nm) are deposited on the samples hydrothermally treated in CaHPO₄ solutions. Energy dispersive x-ray, x-ray photoelectron spectroscopy and x-ray diffraction analyses indicate that the nanocrystallites are composed of hydroxyapatite, which are formed through a dissolution-precipitation reaction. The formation of hydroxyapatite nanocrystallites at the film surface improves hydrophilicity of the coating samples. Potentiodynamic polarization test in the Ca-free Hank's solution demonstrates that the coating samples have better corrosion resistance than the polished one. The calcified titanium samples are expected to possess good biological properties.