The process of electrochemical deposited hydroxyapatite coatings on biomedical titanium at room temperature

Calcium phosphate (CaP) ceramics, especially hydroxyapatite (HA), have received much attention and have been clinically applied in orthopaedics and dentistry due to their excellent biocompatibility. Among several methods for preparing HA coating, electrochemical deposition is a relatively new and possible process. However, documented electrochemical processes were conducted at elevated temperature. In this study, uniform HA coatings have been directly deposited on titanium at room temperature. X-ray diffractometry (XRD) results demonstrated that dicalcium phosphate dihydrate (CaHPO₄·2H₂O, DCPD) was the main component of the coating deposited at lower current densities (1 and 5 mA/cm²). HA structure was obtained at current density above 10 mA/cm² and remained stable after heat treatment at 100–600 °C for 1 h. Part of HA phase was transformed into β-TCP and became a biphasic calcium phosphate coating after annealing at 700 °C. Scratch tests showed that HA coating was not scraped off until a shear stress of 106.3 MPa. Coatings deposited at room temperature exhibited stronger adhesion than those at elevated temperature. HA coating revealed a dense inner layer and rough surface morphology which could fulfill the requisition of implant materials and be adequate to the attachment of bone tissue.