Galvanostatic pulse deposition of hydroxyapatite for adhesion to titanium for biomedical purposes

Calcium phosphate coatings, in particular synthetic hydroxyapatite, are applied to the surfaces of titanium and its alloys so as to improve the biocompatibility and biological performance. Currently, plasma spraying is the clinically accepted technique for the deposition of calcium phosphate onto titanium. Electrochemical cathodic deposition is emerging as an alternative technique due to it being a nonline-of-sight technique. In this present study, it is demonstrated that increased thickness, crystallinity and adhesion of calcium phosphate coating on titanium is achieved by periodic pulsed low current densities compared to a constant current deposition method. It is believed that the “off” part of the AC deposition cycle gives the calcium and phosphate ions in the bulk solution sufficient time to diffuse to the titanium's surface maintaining more favourable conditions for HA growth. Unfortunately, although pulsed deposition at high current densities is able to produce thick coatings it cannot avoid problems associated with hydrogen bubbles and thus both AC and DC films deposited at high current densities have low crystallinity and poor adhesion.