Spark anodising of titanium for biomedical applications

Abstract

Spark anodising of titanium enables fabrication of coatings with potential biocompatibility. In the present study, coatings were produced in electrolytes containing various amounts of CaHPO₄, Ca(H₂PO₄)₂, Na₆P₆O₁₈ and Ca(CH₃COO)₂. The findings disclose formation of coatings with compositions, morphologies and structures dependent upon the growth conditions. Calcium and phosphorus species are distributed throughout most of the coating thickness, with typical Ca/P atomic ratios of ∼0·45 and (Ca+P)/Ti atomic ratios in the range 1·0–2·6 in the near surface regions. Calcium contents in particular reduced towards the metal. Dissolution behaviour in physiological solution was investigated by potentiodynamic polarisation measurements and immersion tests, the latter indicating titanium loss rates of ∼0·3 μg cm⁻² day⁻¹. Preliminary adhesion studies using primary human osteoblast cells revealed favourable cell responses to the anodic coatings. Further, the deposition of hydroxyapatite by cathodic deposition in selected electrolytes indicates scope for additional tailoring of coating surfaces. More limited studies of Ti–6Al–4V alloy demonstrated coating formation broadly similar to that on titanium, but with incorporation of aluminium and vanadium species and increased loss rates of titanium, ∼4 μg cm⁻²day⁻¹, in immersion tests.

Keywords:

• TITANIUM
• SPARK ANODISING
• BIOACTIVE COATINGS
• HYDROXYAPATITE