The bone tissue compatibility of a new Ti-Nb-Sn alloy with a low Young's modulus.

A Ti-Nb-Sn alloy was developed as a new β-type titanium alloy which had a low Young's modulus and high strength. The Young's modulus of the Ti-Nb-Sn alloy was reduced to about 45 GPa by cold rolling, much closer to human cortical bone (10-30 GPa) than that of Ti-6Al-4V alloy (110 GPa) and other β-type titanium alloys developed for biomedical applications. The tensile strength of the Ti-Nb-Sn alloy was increased to a level greater than that of Ti-6Al-4V alloy by heat treatment after severe cold rolling. In this study the cytotoxicity of Ti-25Nb-11Sn alloy was evaluated in direct contact cell culture tests using metal disks and the bone tissue compatibility - examined using metal rods inserted into the medullary canal of rabbit femurs. The remarkable findings were that: (1) there were no significant differences in the relative growth ratio and relative absorbance ratio between cells grown with the Ti-Nb-Sn alloy, Ti-6Al-4V alloy and CP-Ti in direct contact cell culture tests; (2) there were no significant differences in the load at failure between the Ti-Nb-Sn alloy and Ti-6Al-4V alloy in pull-out metal rods tests; (3) there were no significant differences in new bone formation around metal rods between the Ti-Nb-Sn alloy and Ti-6Al-4V alloy in histological evaluations. The new Ti-Nb-Sn alloy with an elasticity closer to that of human bone is thus considered to be bioinert while also having a high degree of bone compatibility similar to that of Ti-6Al-4V alloy.