Biocompatible Nanotube-Strontium/polydopamine-arginine–glycine–aspartic acid coating on Ti6Al4V enhances osteogenic properties for biomedical applications

Titanium (Ti) alloys, particularly Ti 6 Al 4 V, are the most commonly used biomedical implant material. Ti alloys are biologically inert, so there have been continuous efforts to improve their osteogenic properties and clinical performance. Since TiO 2 nanotubes (NT) appear to be excellent drug platforms, and strontium reportedly enhances osteogenesis, we constructed a TiO 2 nanotube coating on the surface of Ti 6 Al 4 V and immersed it in Sr (OH) 2 solution in order to incorporate Sr into TiO 2 nanotubes (NT-Sr). The results of field emission scanning electron microscope and X-ray diffraction analysis verified the fabrication of NT-Sr. We next added polydopamine (PDA) and cyclo- (arginine–glycine–aspartic acid–phenylalanine–cysteine) [c(RGDfC)] peptides to further promote biocompatibility of the implant. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy confirmed the existence of PDA and c(RGDfC). Mesenchymal stem cells (MSCs) were planted on Ti, NT, NT-Sr, NT-Sr/PDA, and NT-Sr/PDA-RGD surfaces. The adhesion and differentiation of MSCs on different surfaces were evaluated. The mRNA expression of alkaline phosphatase, runt-related transcription factor 2 (Runx2) and type I collagen (Col I) of different groups were also tested. Finally, we observed that the NT-Sr/PDA-RGD group showed significantly better performance than other groups in terms of the differentiation and osteogenesis-related gene expression of MSCs. Thus, the NT-Sr/PDA-RGD complex may be an important modification strategy for Ti, as it shows excellent osteogenic potential.