Constructing a novel three-dimensional scaffold with mesoporous TiO2 nanotubes for potential bone tissue engineering

Three-dimensional (3D) nanofibrous scaffolds for tissue engineering have been widely studied while 3D scaffolds made of nanotubes are rarely reported. Herein, we report a novel 3D porous network-structured scaffold built of mesoporous TiO2 nanotubes. The TiO2 nanotubes were synthesized using the templateassisted sol-gel method followed by calcination. Bacterial cellulose (BC) with 3D network structure was used as the template. TEM observation confirms the formation of tubular TiO2 nanotubes. The as-synthesized TiO2 nanotubes exhibit an average outer diameter of less than 100 nm and mesoporous walls consisting of aggregated TiO2 nanoparticles with a size of around 7 nm. SEM and TEM observations reveal that the TiO2 nanotube scaffold possesses 3D porous network structure and the surfaces of TiO2 nanotubes are rugged with nanotopography. Additionally, the scaffold built of mesoporous nanotubes with a mesopore size of 3.3 nm exhibits an extremely large surface area of 1629 m(2) g(-1). The capacity of the scaffold to support cell proliferation and osteogenic differentiation was evaluated using CCK-8 assay, alkaline phosphatase (ALP), and calcium content assay. The scaffold shows enhanced cell growth and proliferation and improved ALP activity and mineralization compared to the TCPS (tissue culture plate) control. Furthermore, the ALP activity of the scaffold is as high as a hydroxyapatite-coated nanofibrous scaffold. The enhanced proliferation and osteogenic differentiation of the TiO2 nanotube scaffold is ascribed to the outer surface roughness of TiO2 nanotubes, 3D porous network structure, mesopores, and large surface area.