Bioactivity of hydrothermal-electrochemically deposited apatite in vitro and in vivo

Hydroxyapatite needles were formed on pure titanium plates using the hydrothermal-electrochemical method in an autoclave with two electrodes. The current was kept at 12.5 mA/cm(2) for 1 h in an electrolyte containing Ca and phosphate ions maintained at 100, 150, and 200 degreesC. Titanium plates coated with the hydrothermal-electrochemically deposited apatite at 100 degreesC showed the largest weight gain after immersion in a simulated body fluid at 37 degreesC for 3-27 weeks. Furthermore, the specimens coated at 100 degreesC showed the largest weight loss after immersion in 0.01N HCl solution for 1 - 16 hours. There were no significant differences in the pull-out bonding strength of titanium bars coated at 100, 150, and 200 degreesC to rabbit femora after 3-week implantation. All the hydrothermal-electrochemically deposited apatite showed an excellent biocompatibility. The new bone grew into the boundary between titanium substrate and deposited apatite from the outer surface. At 3-week implantation, the boundary at 100 degreesC was completely filled with the new bone, whereas that at 200 degreesC was not yet filled with it.