Biofunctionalization of SLM Ti–40Nb alloy through hydroxyapatite-modified plasma electrolytic oxidation coating

This study reports the successful development of bioactive coatings on in-situ alloyed Ti-40Nb substrates fabricated via selective laser melting (SLM) using plasma electrolytic oxidation (PEO). Two electrolytes were employed for PEO processing: phosphate–silicate (PS) and phosphate–silicate–hydroxyapatite (PSHA). A comparative evaluation was performed to investigate the influence of electrolyte composition on surface morphology, corrosion resistance, and biological performance. The incorporation of hydroxyapatite (HAp) in the PSHA electrolyte significantly modified the coating structure, resulting in reduced porosity, increased surface roughness, and enhanced wettability. X-ray diffraction analysis confirmed the formation of TiO₂ (anatase and rutile) and Nb₂O₅ phases, with a higher rutile fraction observed in the HAp-incorporated coatings due to intensified plasma discharges. Electrochemical testing in simulated body fluid (SBF) demonstrated improved corrosion resistance for the HAp-containing samples, as evidenced by lower corrosion current density and passivation current values. In vitro assays with MC3T3 pre-osteoblast cells further revealed superior cell viability and proliferation on the HAp-incorporated coatings, attributed to the synergistic effects of roughened topography and the sustained release of bioactive ions. Overall, the PEO-modified Ti40Nb samples exhibited enhanced corrosion protection and cytocompatibility, underscoring their strong potential as next-generation Ti-based orthopedic implant materials.