Porous TiO₂ Nanotube Arrays for Drug Loading and Their Elution Sensing

Porous TiO₂ nanotube arrays have been attracting much attention as optical sensing layers and surface layers of dental implants because they are stable in acid and biocompatible. To use them as the optical sensing layers, TiO₂ nanotube arrays with various structures were fabricated and obtained an optimized microstructure at 50 V, 50 min and 0.5 wt% of NH4F, 7.4 vol% deionized water in ethylene glycol. TiO₂ nanotube arrays which had diameters of ~73.54 nm and lengths of ~3.39 μm showed the best sensing performance. A Ti implant was also anodized at 60 V for 4 hr in an ethylene glycol electrolyte and TiO₂ nanotube arrays showed the pore diameter of 156.01 nm and the thickness of 6.87 μm. Recombinant human bone morphogenetic protein-2 (rhBMP-2), isobutylphenyl propionic acid, and sodium alendronate were loaded into the TiO₂ nanotube arrays on the surface of the Ti implant. For elution of these drugs, optical thickness changes of 2.4 nm, 3.5 nm and 3.1 nm were respectively observed for about 2.2 hr, 3.6 hr and 3.1 hr. The TiO₂ nanotube arrays were useful for drug loading and their elution interferometric sensing.