Osteogenic and angiogenic activities of silicon-incorporated TiO₂ nanotube arrays

Osteogenesis and angiogenesis that have interaction in vivo are two pivotal processes for implant osseointegration, so implant surfaces with both enhanced osteogenic and angiogenic activities are in need. Developing silicon (Si) doped TiO₂ nanotube array (TNA-Si) coatings shall be a promising strategy to yield favorable implant osseointegration with the combined effects of TiO₂ nanotube arrays (TNAs) and Si in the enhancement of both osteogenic and angiogenic activities. To achieve this purpose, TNA-Sis are fabricated through the unique strategy of anodization of magnetron-sputtered TiSi coatings. Under optimized conditions, a highly ordered nanotubular structure with even dispersion of Si throughout the nanotubes in the form of SiO₂ can be obtained. Si incorporation has little influence on the nanotube length, but slightly decreases the diameter, thickens the nanotube wall, and increases the hydrophilicity. TNA-Sis show good cytocompatibility to both osteoblasts and endothelial cells (ECs). TNA-Sis show enhanced proliferation, spreading, alkaline phosphatase activity, collagen secretion, and matrix mineralization of osteoblasts. Meanwhile, TNA-Sis induce better EC proliferation, and the conditioned culture media from TNA-Sis generate better angiogenic ability, nitric oxide production, and vascular endothelial growth factor secretion from ECs. In particular, TNA-Si4.6 with the strongest osteogenic and angiogenic activities in the context of the present study is highly promising as the next-generation hard tissue implant coating.