In vitro corrosion performance of PEO coated Ti and Ti6Al4V used for dental and orthopaedic implants

The present work describes the characteristics of 5–10 μm-thick plasma electrolytic oxidation (PEO) coatings with graded Ca/P ratio generated on titanium of commercial grades I (c.p. Ti) and V (Ti6Al4V) and some of the aspects of their bioactivity and corrosion resistance in vitro in long-term (up to 8 weeks) normal and short-term (1 week) inflammatory conditions. Simulated body fluid (SBF) and artificial saliva at 37 °C were used as corrosive media; inflammatory conditions were simulated by controlling the pH and introducing hydrogen peroxide (usual metabolism product of inflammation-inducing bacteria). Additionally, the saliva was modified with fluoride ions. DC and AC electrochemical tests were used to characterize the corrosion protection mechanism of the coatings. Metal ion release (Ti^{4 +}, Al^{3 +} and V^{5 +}) from PEO coated materials during their in vitro immersion in normal and inflammatory SBF was evaluated by ICP-MS. PEO coatings on Ti6Al4V alloy inhibited the liberation of titanium compared with non-coated alloy both at short-term inflammatory and long-term normal immersion conditions; but the liberation of aluminium and vanadium was greater from the coated than non-coated alloy at both conditions, due to the presence of these ions in the coatings. The PEO-coated c.p. Ti exhibited considerably higher stability with respect to Ti^{4 +} ion release in SBF at all conditions compared with the PEO-coated Ti6Al4V.