Micro Patterning Processes for Thin Film Nitinol Endografts and Evaluation of Endothelialization in Swine Model

Micro features were created in thin film nitinol using a novel lift-off process to create an endovascular biomedical device. This manuscript describes fabrication problems with wet etching and introduces an effective way, named "Lift-off" process to solve undercut and non-uniform pattern issues. Two lift-off processes (i.e., lift-off I and II) are discussed. Lift-off I process has fracture issues and the film peels off the substrate due to high aspect ratio post structures. Lift-off II process use the film on the top of the Si substrate to fabricate various shape patterns (i.e., ellipse, diamond, circle, square, etc.) in the range of 5 similar to 60 mu m. The lift-off II process shows smooth and well aligned micro patterns in thin film nitinol. In-vivo tests in swine were performed to evaluate the endothelial tissue growth through fabricated micro patterns. Angiography and SEM images show patency of the artery and a uniform endothelial layer covering the device without thromobosis.