Surface modification of TiO₂ nanotubes with osteogenic growth peptide to enhance osteoblast differentiation

To investigate the influence of surface-biofunctionalized substrates on osteoblast behavior, a layer of aligned TiO₂ nanotubes with a diameter of around 70nm was fabricated on titanium surface by anodization, and then osteogenic growth peptide (OGP) was conjugated onto TiO₂ nanotubes through the intermediate layer of polydopamine. The morphology, composition and wettability of different surfaces were characterized by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and contact angle measurements, respectively. The effects of OGP-modified TiO₂ nanotube substrates on the morphology, proliferation and differentiation of osteoblasts were examined in vitro. Immunofluorescence staining revealed that the OGP-functionalized TiO₂ nanotubes were favorable for cell spreading. However, there was no significant difference in cell proliferation observed among the different groups. Cells grown onto OGP-functionalized TiO₂ nanotubes showed significantly higher (p<0.05 or p<0.01) levels of alkaline phosphatase (ALP) and mineralization after 4, 7 and 14days of culture, respectively. Cells grown on OGP-functionalized TiO₂ nanotubes had significantly higher (p<0.05 or p<0.01) expression of osteogenic-related genes including runt related transcription factor 2 (Runx2), ALP, collagen type I (Col I), osteopontin (OPN) and osteocalcin (OC) after 14days of culture. These data suggest that surface functionalization of TiO₂ nanotubes with OGP was beneficial for cell spreading and differentiation. This study provides a novel platform for the development and fabrication of titanium-based implants that enhance the propensity for osseointegration between the native tissue and implant interface.