Nanograins on Ti-25Nb-3Mo-2Sn-3Zr alloy facilitate fabricating biological surface through dual-ion implantation to concurrently modulate the osteogenic functions of mesenchymal stem cells and kill bacteria

Surface mechanical attrition treatment (SMAT) method is an effective way to generate nanograined (NG) surface on Ti-25Nb-3Mo-2Sn-3Zr (wt.%) (named as TLM), a kind of β-type titanium alloy, and the achieved nanocrystalline surface was proved to promote positive functions of osteoblastic cells. In this work, to further endow the NG TLM alloy with both good osteogenic and antibacterial properties, magnesium (Mg), silver (Ag) ion or both were introduced onto the NG TLM surface by ion implantation process, as a comparison, the Mg and Ag ions were also co-implanted onto coarsegrained (CG) TLM surface. The obtained results show that subsequent ion implantation does not remarkably induce the surface roughness and topography alteration of the SMAT-treated layers, and it also has little impact on the microstructure of the SMAT-derived β-Ti nanograins. In addition, the implanted Mg and Ag ions are observed to exist as MgO and metallic Ag nanoparticles (NPs) embedding tightly in the β-Ti matrix with grain size of about 15 and 7 nm, respectively. Initial cell adhesion and functions (including proliferation, osteo-differentiation and extracellular matrix mineralization) of rabbit bone marrow mesenchymal stem cells (rBMMSCs) and the bacterial colonization of Staphylococcus aureus (S. aureus) on the different surfaces were investigated. The in-vitro experimental results reveal that the Mg and Ag single-ion implanted NG surface either significantly promotes the rBMMSCs response or inhibits the growth of S. aureus, whereas the Mg/Ag co-implanted NG surface could concurrently enhance the rBMMSCs functions as well as inhibit the bacterial growth compared to the NG surface, and this efficacy is more pronounced as compared to the Mg/Ag co-implantation in the CG surface. The SMAT-achieved nanograins in the TLM surface layer are identified to not only play a leading role in determining the fate of rBMMSCs but also facilitate fabricating dual-functional surface with both good osteogenic and antibacterial activities through co-implantation of Mg and Ag ions. Our investigation provides a new strategy to develop high-performance Ti-based implants for clinical application.