Deposition of hydroxyl-apatite on titanium subjected to electrochemical plasma coating

This work investigated the direct deposition of hydroxyl-apatite (HA) on pure titanium via an electrochemical plasma (EP) coating. For this purpose, the EP coatings were deposited at 200 mA/cm2 for 900 s in HA-containing electrolytes with and without tripotassium phosphate (K3PO4). At the onset of the ignition phenomenon during the EP coatings, the HA particles began to nucleate on the titanium sample due to the electrophoresis of the negatively charged HA particles in both electrolytes. The amounts of Ca and P in the coating layer produced in the electrolyte without K3PO4 was higher than that in the electrolyte with K3PO4 since the HA coating layer grew without a transformation in case of the electrolyte without K3PO4. In contrast, most HA particles in the coating layer of the electrolyte with K3PO4 decomposed readily to α-, β-tricalcium phosphate (Ca3(PO4)2) and calcium titanate (CaTiO3) compounds with the aid of the plasma-assisted electrochemical reactions found between the HA particles and phosphate ions or titanium oxide. Immersion tests in a simulated body fluid solution showed that the titanium samples coated with the biochemically stable HA particles, which were formed in the electrolyte without K3PO4, exhibited the accelerated growth of biomimetic apatite.