In vitro biocompatibility of Ni-Free Ti-based shape memory alloys for biomedical applications

This study was undertaken to evaluate the in vitro biocompatibility of newly developed Ni-free Ti-based shape memory alloys (SMAs) in comparison to that of commercial pure titanium (cpTi). This study compared Ti-24 mol%Nb-3 mol%Al (Ti-Nb-Al) and Ti-7 mol%Cr-3 mol%Sn (Ti-Cr-Sn) to cpTi from a cell-compatibility perspective. In all, 63 samples (21 samples for each group) were prepared, which were machined into 10-mm-diameter, 0.15-mm-thick, mirror-polished disks. Their surface morphology was evaluated using scanning electron microscopy (SEM). The chemical composition of the sample surface was determined using an energy dispersive X-ray analyzer (EDX). Sample surface roughness was measured using a non-contact 3D profiler. After sample surface observations, the cell proliferation and viability of African green monkey kidney fibroblast cell line COS7 in direct contact with these new alloys were evaluated by DNA quantification, by live cell imaging using CelLuminate Red fluorescent cell stain as a new method, and by cytoskeletal observations by immunofluorescent actin labelling. Cell proliferation was examined after 1,3, and 5 days of culture. Results were the following. (i) Each sample showed high purity and a very smooth surface, showing no morphological differences among groups. (ii) The COS7 cells took in sufficient CelLuminate Red to visualize the cells using epifluorescent microscopy, and (iii) cell proliferation with Ti-Cr-Sn was lower than with either cpTi or Ti-Nb-Al. These results suggest that Ti-Nb-Al alloy showed biocompatibility as high as that of cpTi and that it is more suitable for biomedical applications.