FIB patterning of stainless steel for the development of nano-structured stent surfaces for cardiovascular applications

Coronary artery disease is a major problem worldwide. Stent implantation is a percutaneous interventional procedure that mitigates vessel stenosis, providing mechanical support within the artery. However, stenting causes physical damage to the arterial wall. The research presented here develops novel nano-structured features on stent surfaces to promote rapid endothelial cell adhesion to reduce in-stent re-stenosis. Nano-structured features (concaves) ordered in rectangular arrays were patterned on 316L Stainless Steel (SS) surfaces using focused ion beam (FIB) milling after electropolishing using linear sweep voltammetry and chronoamperometry. Various dose test experiments were performed, aiming at an array of 120 nm diameter holes with pitch of 240 nm and depth of 50-100 nm on sample area of 400 μm x 400 μm. Studies on FIB milling rates were carried out to optimise the time and to create a uniform array of holes. Based on the SEM examination of the hole arrays (plane view and cross section) it can be concluded that a low ion beam current created well shaped uniform concave structures (Gaussian shape) with good depth profile, while a high current resulted in an array of holes with sine profile. Further, a higher current created larger diameter holes with less defined depth profile and deviation from Gaussian shape. We demonstrate that the ability to perform nano-structuring with FIB milling is greatly affected by the polycrystalline nature of SS.