Formation of nanotubular structure on low-modulus Ti–7.5Mo alloy surface and its bioactivity evaluation

Highlights: • Nanotubes on Ti–7.5Mo surface were fabricated by anodic oxidation in NaCl/NH₄F. • A tube length of 550 nm at 5 V and 700 nm at 10 V on Ti–7.5Mo surface. • Components on annealed nanotubes of Ti–7.5Mo surfaces were TiO₂, MoO₂, and MoO₃. • After soaking in SBF, CaP layer covered the entire nanotubular surface within 1 d. -- Abstract: This study investigates the use of anodization in NH₄F/NaCl electrolyte in the formation of self-assembled nanotube arrays on a Ti–7.5Mo surface. As anodic oxidation potential increased from 5 V to 10 V, the pore size and tube length of the nanotubes gradually increased approximately from 23–27 to 31–44 nm, and 550 to 700 nm. The XRD results indicated that the oxide layers on the surface of the anodized samples were all amorphous structures. After annealing at 450 °C for 3 h, peaks of anatase phase were observed. The results of the XPS analysis showed that the major components on the surfaces of the annealed nanotube arrays were TiO₂, MoO₂, and MoO₃. In vitro testing of the annealed nanotube arrays demonstrated that rapid deposition of apatite spheroids on these nanostructures occurred after only 12 h immersion in simulated body fluids (SBF), a result that was particularly evident in the samples anodized at 10 V. Cell culture experiments showed that the anodized Ti–7.5Mo alloy is biocompatible and can support cell attachment.