Structure and Adhesion of Hydroxyapatite Films Electrochemically Deposited onto Titanium Substrates under Short-Pulse Current in Metastable Calcium Phosphate Solution

Abstract

Hydroxyapatite (HA) films were deposited onto titanium (Ti) metal substrates by an electrodeposition method under a short-pulse current. Metastable calcium phosphate solution was used as the electrolyte. The ion concentration of the solution was 1.5 times that of human body fluid, but the solution did not contain magnesium ions at 36.5°C. We used an average current density of 0.01 A/cm2 and current-on time (TON) equal to current-off time (TOFF) of 10 ms, 100 ms, 1 s, and 15 s. The adhesive strength between HA and Ti substrates were relatively high at TON = TOFF = 10 ms. It is considered that small calcium phosphate crystals with low crystallinity were deposited on the Ti surface without reacting with other calcium phosphate crystals, H2O, and HCO3– in the surrounding environment. This resulted in relaxation of the lattice mismatch and enhancement of the adhesive strength between the HA crystals and Ti substrates.