Laboratory method for preparing hydroxyapatite bioceramic coating

Hydroxyapatite bioceramic can be coated on metal substrate. But the technologies suffer from three defects: (1) high cost of HAP powder, (2) decomposition of HAP under high temperature and (3) lack of uniformity in thickness of coating. These three defects were greatly reduced through a new preparation method of HAP coating, in which original coating was first deposited on metal substrate with electrocrystallization and then turned into HAP with hydrothermal treatment. Deposition of original coating on titanium was accomplished with potentiostat. The anode was graphite rod and the cathode was titanium. Water solutions of Ca(NO₃)₂ and NH₄H₂PO₄ were mixed, and pH value of electrolyte was adjusted with NH₃·H₂O. XRD indicated that original coating consisted completely of CaHPO₄·2H₂O. After hydrothermal treatment, coating consisted of both HAP and CaHPO₄·2H₂O whose percentages were 90.5% and 9.5% respectively. Thus hydrothermal treatment can indeed turn CaHPO₄·2H₂O into HPA. With increasing temperature or increasing pH value of hydrothermal treatment, the transformation into HAP became better. A temperature of 240°C and a pH value of 10 were found to be adequate for 10)% transformation into HAP. SEM indicated that coating thickness was greater than 50μm, and the morphology of crystal grains of such HAP was needle-like, very suitable for implanting into human body for replacement of bone.