Electrochemical cathodic deposition of hydroxyapatite: Improvements in adhesion and crystallinity

To improve on the biological performance of titanium and its alloys hydroxyapatite coatings are applied to the surface. Although plasma spraying is currently the clinically accepted deposition technique, it has drawbacks including being a line-of-site method which greatly limits its uses for coating either irregular-shapes or the low elastic moduli porous materials and metallic sponges now being developed for implants. Electrochemical cathodic deposition is an alternative technique but this also has disadvantages, mainly the crystallinity of the deposited hydroxyapatite and its adhesion to the substrate. In the present study it is demonstrated that increased adhesion and crystallinity are obtained by either pre-treating the Ti substrate with NaOH followed by a heat treatment at 600 °C or the addition of H2O2 to the electrolyte. The increased adhesion is believed to result in the former case from the development of a titanate binding layer. In the latter case the local alkaline conditions required for deposition are obtained from the reduction of the peroxide, thereby negating the need to evolve hydrogen that can damage the film. Rotating the substrate at low revolutions is also beneficial for adhesion however; at high rotation rates bulk precipitation is favoured over film formation.