Hydrothermal calcification of bioglass film in CaHPO4 solutions

• The sol-gel Si-Ca-P bioglass film on titanium is amorphous with a little Ca3SiO5.
• HA nanocrystallites are formed by hydrothermal treatment in CaHPO4 solutions.
• The formed HA nanocrystallites improve hydrophilicity of the coating samples.
• The coating samples have better corrosion resistance than the polished one.

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.