Enhanced biocompatibility of a pre-calcified nanotubular TiO₂ layer on Ti-6Al-7Nb alloy

To optimize the osseointegration of dental implants, TiO₂ nanotube carriers for bioactive molecules, which can accelerate the process of osteoblastic differentiation, have been broadly developed. The aim of this study was to investigate the feasibility of using cyclic pre-calcification in combination with anodizing on Ti-6Al-7Nb alloy and to explore the biocompatibility of modified surface in vitro. Nanotubular samples were fabricated under suitable anodizing conditions before exposure to 20 repeated cycles of immersing in NaH₂PO₄ and Ca(OH)₂ solutions. The characteristics of modified surface were examined using field emission-scanning electron microscopy (FE-SEM), X-ray energy dispersion spectroscopy (EDS) and X-ray diffraction (XRD). The investigation assessed a two-layer modified surface: the porous and rough Calcium-Phosphate covering layer, and the inner, dense nanotube-layer, which was penetrated by grain-like Calcium-Phosphate precipitates. The presence of an apatite-like phase after 2day-immersion in simulated body fluid (SBF) on this surface determined a high bioactivity potential. The modified surface showed a lower corrosion rate (13.2×10^-9mmpy) compared to an untreated one (17.1×10^-8mmpy). The number of viable osteoblasts on treated specimens was significantly higher than that on untreated ones after culturing for 2, 4, and 7days (p<0.05). FE-SEM observation also recorded that the osteoblast morphology at 7day-culturing on treated surface is well-spreading with extensions coming out from the cell. These extensions help the cell anchor itself to the modified structure. In summary, the cyclic pre-calcification method with simple procedure in conjunction with anodization promoted the corrosion resistance, bioactivity, and biocompatibility of Ti-6Al-7Nb alloy, indicating an ideal bioactive method for implant material.