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

Titanium (Ti) alloys, particularly Ti6 Al4 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 TiO2 nanotubes (NT) appear to be excellent drug platforms, and strontium reportedly enhances osteogenesis, we constructed a TiO2 nanotube coating on the surface of Ti6 Al4 V and immersed it in Sr (OH)2 solution in order to incorporate Sr into TiO2 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.