Hydroxyapatite Coating on a Titanium Metal Substrate by a Discharging Method in Modified Artificial Body Fluid

Purpose: The aim of this study was to evaluate the formation of a hydroxyapatite coating on titanium plate by discharging in typical and modified artificial body fluids. Materials and Methods: Japanese Industrial Standard Grade 2 titanium plates were used as specimens. Discharging was performed on the specimens in each solution, and the surface topography of each coating was observed with a scanning electron microscope. The Ca/P atomic ratio and surface characterization of each coating were evaluated by x-ray photoelectron spectroscopy, and crystal phases of each coating were analyzed by Fourier transform infrared spectroscopy and x-ray diffraction. Results: Tricalcium phosphate formed on the titanium surface in a 1.5 Ca/P solution with high ion concentrations of calcium (2.5 mmol/L) and phosphorous (1.67 mmol/L). Crystalline HA was formed on the titanium surface in a 1.5 Ca/P solution (Hanks' balanced salt solution without organic molecules) with low ion concentrations of calcium (1.26 mmol/L) and phosphorus (0.83 mmol/L). Discussion: A solution containing organic pH buffer was insufficient to form stable coatings on the titanium surface. Coating properties strongly depended on the Ca/P chemical ratio of the applied solution. A Ca/P ratio of 1.5 was appropriate for preparing a calcium phosphate coating on a titanium surface, whereas a Ca/P ratio of 2.5 was excessively high. Conclusion: These findings suggest that Hanks' balanced salt solution without organic molecules is the most suitable solution for forming crystalline hydroxyapatite coatings on titanium surfaces by the discharging method.