Osteogenic activity of Na2Ti3O7/SrTiO3 hybrid coatings on titanium

Titanium (Ti) and its alloys have been widely adopted as implant materials due to their satisfactory biocompatibility and favorable mechanical property. However, they usually show poor osteogenic ability, hindering its clinical application. Herein, Na2Ti3O7/SrTiO3 hybrid coatings on Ti were fabricated via one-step alkali etching in a mixed solution of NaOH and Sr(OH)2 to enhance its osteogenic activity. Scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy were used to characterize the samples. Biological experiments were conducted to evaluate their osteogenic activity. The results showed Na2Ti3O7 nanowire coatings could be grown on Ti surface and Sr could be incorporated into the coatings. Incorporation of Sr clustered the nanowires and high Sr content lead to the formation of spherical SrTiO3 with diameter of about 1 μm. Sr2+ could continuously release from the samples and the release amount increased with Sr content in the coatings. Although adhesion, spreading, viability and proliferation of osteoblasts on all the samples had no significant difference when compared with Sr-free one, they could significantly promote osteogenic differentiation as verified by enhanced alkaline phosphatase (ALP) activity, collagen secretion, and extracellular matrix mineralization of osteoblasts. Further studies depicted that the expression levels of osteogenic-related genes including ALP, type I collagen and transforming growth factor-β were significantly upregulated in Sr-containing samples. The desirable osteogenic capacity may be ascribed to the synergistic effect of continuous Sr2+ release and nanostructured morphology. The samples containing Sr of 5.65–11.07 at.% showed the best osteogenic capacity therefore possess great potential in hard-tissue implant field.