Characterization of a calcium phosphate–TiO2 nanotube composite layer for biomedical applications

Well-ordered nanotube arrays of titania ~ 0.7 μm high and about 40 or 110 nm in diameter were prepared via electrochemical oxidation at constant voltage (10, 15, 20 or 25 V) in a mixture of 0.86 wt.% of NH4F, glycerol and deionized water. The effect of annealing the nanotubes at 600 °C on their morphology and structure was examined using SEM and TEM techniques. These substrates are suitable supports for a calcium phosphate coating deposited by a simple immersion in Hank solution.The nucleation and growth of a calcium phosphate (Ca–P) coating deposited on TiO2 nanotubes (NT) from Hanks' solution was investigated using SEM. XPS and FTIR surface analytical techniques were used to characterize the self-organized porous TiO2 layers covered with calcium phosphate coatings before and after protein adsorption. Our results confirm that the nanotubular titania layer became stable after annealing at 600 °C, while its internal structure changed from amorphous to crystalline anatase, and eventually, a mixture of anatase and rutile. These thermally stabilized TiO2 nanotubes significantly enhance apatite formation in Hanks' Balanced Salt Solution as compared to pure Ti covered with a native oxide layer. The Ca–P/TiO2 NT/Ti surface adsorbs a higher amount of protein (bovine serum albumin, BSA) for a geometric surface area than does the Ti surface. The above difference in protein adsorption suggests a more promising initial cellular response for a Ca–P/TiO2 NT/Ti composite than for a typical Ti implant surface.