Directional Copper Decoration of Spaced TiO ₂ Nanotubes Enables Geometry-Controlled Ion Release and Antibacterial Response

Anodic titanium dioxide (TiO₂) nanotubes (NTs) are well-established implant coatings owing to their nanoscale tunability, osteogenic support, and long-term biocompatibility. However, reproducible approaches that directly link NT geometry with controlled antibacterial functionality and tunable ion release remain limited. Here, we present a spatially selective, geometry-defined copper (Cu) decoration strategy for morphology-defined spaced NTs with an intertube spacing of 70-214 nm and a diameter of ∼145 nm. These NTs were fabricated via fluoride-containing diethylene glycol-based anodization. Directional sputtering was used to deposit Cu as either conformal wall coatings, the common physical vapor deposition configuration, or as discrete top caps, perpendicular to the sputtering target configuration, thus enabling precise control of the Cu metal localization on/in the spaced NTs. Morphology-composition correlations, confirmed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and focused ion beam scanning electron microscopy (FIB-SEM), revealed a clear depth confinement for the cap-decorated NTs versus an extended distribution in the case of the conformal coatings. Inductively coupled plasma atomic emission spectroscopy (ICP-AES) showed that ∼1 atom % Cu, the antibacterial/cytocompatibility threshold in the literature, generated sustained ion release with early bacterial suppression. Higher loadings accelerated Cu²⁺ release but produced variable long-term inhibition, which can be correlated with the Cu configuration type. This geometry-directed sputtering approach provides a reproducible route for spatially controlled Cu placement, with a link between NT geometry, Cu localization, and antibacterial behavior, thus applicable for designing future multifunctional implant surfaces with controlled therapeutic release. It also provides a reproducible strategy for designing future multifunctional, release-tunable implant surfaces.