Assessment of endothelial cell growth behavior in thin film nitinol

Growing clinical needs for less invasive endovascular treatments necessitate the development of advanced biomaterials that exhibit low-profile and enhanced biocompatible properties. One of the endovascular devices is a stent graft, which contains a metallic backbone, covered with thin polymeric membranes such as Dacron® and expandable polytetrafluoroethylene (ePTFE). This device has been widely used for treating various vascular diseases and injuries. While the commercial materials including Dacron® and ePTFE have demonstrated a good feasibility, they were found to induce inflammatory vessel wall reactions with neointimal hyperplasia. Consequently, it causes re-narrowing of the lumen space and thrombogenic issues that ultimately lead the treatment failure. In this paper, we introduced a thin film nitinol (TFN) as an alternative graft material and evaluated the growth behavior of endothelial cells (EC) both qualitatively and quantitatively. As a proof-of-concept study, both untreated nonpatterned film (TFN) and surface treated TFN (S-TFN) materials were used. We compared the adhesion, growth, and proliferation of ECs on a solid (non-patterned) TFN with the two most widely-used commercial graft materials (Dacron® and ePTFE). The in vitro experimental results showed better adhesion and growth of ECs on TFN materials than either ePTFE or Dacron®. Specifically, S-TFN showed approximately twice number of ECs attached on the surface than any other materials tested in this study. In addition, in vivo swine study demonstrated that ECs had a relatively high proliferation on the micropatterrned S-TFN with ~50% surface coverage within two weeks. Both in vitro and in vivo study results of cell growth suggested that TFN materials could be a promising graft material for low-profile endovascular devices.