Cytocompatibility of various metal and development of new titanium alloys for medical implants

The cytocompatibility of new Ti alloys not containing Al and V such as Ti–15%Zr–4%Nb–4% Ta–0.2%Pd–0.05%N–0.2%O and Ti–15%Sn–4%Nb–2%Ta–0.2%Pd–0.2%O were investigated by comparing with those of pure Ti grade 2 and Ti–6%Al–4%V ELI (Extra Low Interstitial) alloys. The relative growth ratio for the medium extraction of Al containing very little V ions (less than 0.02 mass ppm) was too low as compared to that of V free Al extraction. However, mixed powder extraction such as Ti+Zr+Nb+Ta and Ti+Sn+Nb+Ta exhibited evidently no effect on the relative growth ratio of L929 cells. The relative growth ratios of both L929 and MC3T3-E1 cells for the new Ti alloys were almost equal to 1 and were slightly higher than pure Ti grade 2 and Ti–6%Al–4%V ELI alloys. Also, the influence of extracting with Eagleʹs minimum essential medium (MEM) solution for L929 cells and ultra pure water for MC3T3-E1 cells on the relative growth ratio of cells were examined. Further, wear tests were conducted with the new Ti alloys, pure Ti grade 2 and Ti–6%Al–4%V ELI alloy disks against apatite ceramics and alloy pins in Eagleʹs MEM solution. The relative growth ratios of L929 and MC3T3-E1 cells were estimated with these wear test solutions. The relative growth ratio of L929 cells were almost equal to 1 for the new Ti alloys and pure Ti grade 2 against apatite ceramics pin up to 105 cycles. However, the relative growth ratios of L929 and MC3T3-E1 cells sharply decreased for Ti–6%Al–4%V ELI disk against apatite ceramics pin from 3×104 wear cycles. It was observed that the pH of the Eagleʹs MEM solution gradually increased as the number of wear cycles increased in all the cases of alloy disk against apatite ceramics pin. Also, the V ion concentration increased as the number of wear cycles increased. This result was also similar for MC3T3-E1 cells. Further, the relationship between metallic concentration in the medium extracted with Ti, Al, V, Zr, Sn, Nb, Ta, and Pd powders and the relative growth ratios of L929 and MC3T3-E1 cells were evaluated. A similar dependence of the concentration of vanadium ion and the relative growth ratios of L929 and MC3T3-E1 cells were seen as in the case of the wear tests.