Tailoring TiO2 Nanotube Arrays via Anodization Voltage and Thermal Processing: A Parametric Design Roadmap for Customizable Biomedical Applications

Background/Objectives: Titanium and its flagship alloy (Ti6Al4V) represent the clinical gold standard for orthopedic and dental implants; however, optimizing their surface architecture to serve as high-capacity, reliable platforms for localized therapeutic delivery remains a significant clinical challenge. In this study, we aim to establish a systematic design roadmap linking surface engineering parameters directly to functional drug delivery performance. Methods: To achieve this, a comparative investigation was performed to map the electrochemical growth kinetics, voltage-driven morphological evolution, and processing limits of TiO2 nanotube (TNT) arrays developed on commercially pure titanium (CP-Ti) and Ti6Al4V substrates in an ethylene glycol-based electrolyte containing NH4F. Anodization was carried out at three different potentials (40 V, 50 V, and 60 V) for 30 min, followed by structural and statistical evaluation. Results: Scanning electron microscopy (SEM) combined with Gaussian size-distribution modeling confirmed a strong linear correlation between applied potential and pore dimensions, expanding mean diameters from 59 nm to 88 nm on CP-Ti and from 56 nm to 96 nm on Ti6Al4V. Current–time (I-t) transient analysis revealed distinct growth kinetics, with Ti6Al4V exhibiting enhanced current fluctuations driven by the differential oxidation rates of its dual-phase (α + β) microstructure. Furthermore, post-anodization thermal annealing at 450 °C is identified as a necessary structural processing step to stabilize the amorphous layers into crystalline polymorphs, providing the essential capillary stress resistance required to prevent film delamination during fluidic drug loading (MgSO4 simulation). Conclusions: By establishing a comprehensive parameter-property matrix, this study provides a practical design roadmap that categorizes specific anodization regimes for tailored pharmaceutical and biomedical functions, ranging from direct osteoblast adhesion (40–50 V) to superhydrophilic architectures structurally optimized for high-capacity drug delivery (60 V).