Potential-controlled electrochemical deposition of hierarchical hydroxyapatite/TiO2 nanotube coatings for biomedical applications.

Hydroxyapatite (HA) coatings on TiO₂ nanotube arrays have attracted considerable interest for improving the bioactivity of titanium implants. However, the influence of electrodeposition potential on coating formation and its correlation with the structural, electrochemical, and biological performance of HA/TiO₂ coatings remains insufficiently understood. In this study, HA coatings were electrodeposited onto anodized TiO₂ nanotube arrays at deposition potentials ranging from 1 to 9 V. The coatings were systematically characterized in terms of morphology, phase composition, surface properties, corrosion resistance, apatite-forming ability, and in vitro cytocompatibility. Low deposition potentials (1-5 V) produced discontinuous HA deposits, whereas an excessive potential (9 V) resulted in non-uniform crystal growth. In contrast, deposition at 7 V generated a homogeneous hierarchical micro/nanostructure with superhydrophilic wettability, improved coating adhesion, enhanced corrosion resistance, rapid apatite formation in simulated body fluid, and superior cell attachment and extracellular matrix protein deposition. These findings demonstrate that deposition potential governs the structure-property relationship of electrochemically deposited HA/TiO₂ coatings and identify 7 V as the optimal condition for achieving balanced physicochemical, electrochemical, and biological properties. The optimized HA/TiO₂ coating shows promising potential for bioactive surface modification of biomedical implants.