Antibacterial, osteogenic, and angiogenic activities of SrTiO₃ nanotubes embedded with Ag₂O nanoparticles

Biomedical titanium (Ti) implants with good anti-infective, osteogenic, and angiogenic properties are in great demand. SrTiO₃ nanotubes (NTs) are embedded with silver oxide (Ag₂O) nanoparticles (NPs) (denoted as NT-Sr-Ag) by a hydrothermal treatment of TiO₂ NTs containing Ag₂O NPs (denoted as NT-Ag) in a Sr(OH)₂ solution. The morphology, composition, microstructure, ion release phenomenon, as well as antibacterial, osteogenic, and angiogenic activities are investigated in details. During the hydrothermal treatment, the amorphous TiO₂ in the NTs morphs into cubic SrTiO₃ gradually and the ordered nanotubular architecture is preserved. Some Ag₂O NPs are incorporated into the structure although some of them dissolve in the solution. Long-term bacterial resistance against Staphylococcus aureus is observed as a result of the prolonged and controllable Ag⁺ release. NT-Sr-Ag can also release Sr²⁺ similarly to stimulate osteoblasts to secrete the vascular endothelial growth factor (VEGF). Both the released Sr²⁺ and secreted VEGF upregulate the alkaline phosphatase (ALP) activity and extracellular matrix mineralization of osteoblasts. Furthermore, better angiogenic activity is observed when endothelial cells are cultured in NT-Sr-Ag conditioned media when compared with that in NT-Ag conditioned media, which is believed to be ascribed to the positive regulation of VEGF secretion of Sr²⁺. NT-2Sr-Ag and NT-3Sr-Ag (Hydrothermal treatment for 2 and 3h, respectively) exhibit excellent antibacterial, osteogenic, and angiogenic activities and are promising in biomedical implants.