Electrochemical and electrophoretic deposition of hydroxyapatite for orthopaedic applications

The basic calcium phosphate mineral, hydroxyapatite (HAP) (Ca₁₀(PO₄)₆(OH)₂), is the prototype of one of the major constituents of bone and teeth. Thin layers of HAP were coated on the surface of type 316L stainless steel by electrophoretic deposition (EPD) from a 2·5% suspension in isopropyl alcohol, and this was followed by vacuum sintering at 800°C for 1 h. The development of HAP coatings was affected by the applied potential and time. In addition, HAP coatings were synthesised on pure Ti by electrochemical deposition and fully characterised to validate their use in orthopaedic implants. Electrodeposition was carried out from a bath containing low concentrations of Ca(NO₃)₂ and NH₄H₂PO₄ at pH 6·0 by cathodic polarisation. Both types of HAP coating were fully characterised, including with respect to corrosion resistance. The advantages of these techniques include: (i) control over the composition and structure of the coating; and (ii) the ability to coat irregular surfaces easily.