To create the material, researchers incorporate dry etching into a silicon substrate followed by deposition of a copper sacrificial layer and SiO2 barrier layer. Thin-film nitinol is deposited on the patterned silicone substrate using a DC (diode) sputtering technique. The result is a 6-µm thin film.
 

To test the material’s antithrombotic properties, the team conducted platelet adhesion studies using healthy human plasma. Results were compared to both Dacron and ePTFE obtained from commercially available stent grafts. All samples were incubated in platelet-rich plasma for 3 hours at 37°C. They were dehydrated and supercritical-point dried before gold sputtering and scanning electron microscopy were used to observe platelet adhesion. The number of platelets per unit area were calculated and the thin-film samples demonstrated no significant platelet adhesion (0~3 per 40 × 40 µm²).
 

For in vivo testing, they mounted the thin film nitinol onto a commercially available stent and deployed it into swine test subjects. Two weeks after deployment, the micropatterned thin film showed a uniform endothelial layer without thrombosis. Postmortem analysis revealed rapid endothelial tissue growth with minimal neointimal cells growing through the patterns of the film.
 

“The thickness of the nitinol is almost nothing,” said Yougjae Chun, who presented the work to attendees at the International Conference of Shape Memory and Superelastic Technologies in May 2010. However, continued development of the material relies on meeting a few challenges. Chun explained that the team is working to have the material support sufficient radial force. In addition, removing stiffness in the material could make it better suited to navigating arteries.