Bone formation at the surface of low modulus Ti–7.5Mo implants in rabbit femur

The biocompatibility of the Ti–7.5Mo alloy was examined, because the alloy has a high-strength/modulus ratio and thus is a potential candidate for orthopedic applications. Cell viability assay using 3T3 cells revealed that the Ti–7.5Mo did not induce apparent cell death, when the cells were grown on disks made of the alloy or incubated with the alloy-conditioned medium at 37 or 72 °C for 24–72 h. The Ti–6Al–4V alloy was used as a control and did not cause apparent cell death either. Moreover, pins of 6 mm long and 2 mm in diameter of Ti–7.5Mo and Ti–6Al–4V were implanted into the left and right rabbit femurs, respectively, for 6, 12 and 26 weeks. New bone tissue grew to surround the pins, which spanned cortical and marrow regions, as shown by toluidine blue-stained bone sections of the three time points. Strikingly, the amount of new bone encircling the Ti–7.5Mo implant was approximate two-folds of that at Ti–6Al–4V by 26 weeks post-implantation. This facilitation of bone formation could be associated with the unique properties, such as a low modulus and the composition of Mo, of the Ti–7.5Mo.