Evolution of Nitinol Stent Technology for Neurovascular Applications – Advancement in Laser Cutting to Post-Processing

The nitinol stents in the Neurovascular space are designed for use as a support structure to embolic coil mass in the treatment of the intracranial aneurysms. Neuroform (Stryker) and Enterprise (J&J) stents, developed about 10 to 12 years ago, are two widely-used stents. Using the Nitinol technology of that time, these stents could only be produced with minimum strut width of about 60 to 75 microns. As a result, these stents have too large a pore size (and small surface area) to provide adequate support to the coil mass.  Particularly, in the treatment of  wide-neck aneurysms, these stents have shown limitations in their ability to secure the coil mass, thereby increasing the risk of coil herniation into the parent artery.  The recent advancement in nitinol technology has made it possible in optimizing some of these key parameters in the development of the next generation neurovascular stent.  These next generation stents with optimized pore size and surface area have been shown to be significantly more effective in securing the embolic coil mass, and particularly, in treating wide-neck aneurysms. This paper will share a novel stent design concept and recent improvements in nitinol technology enabling the development of next generation neurovascular stents.  A study to evaluate the change in the flow pattern inside a silicone aneurysm model was performed using Particle Imaging Velocimetry (PIV) techniques shows 82% reduction in mean velocity and mean vorticity due to the design of new stents. A Preliminary Computational Fluid Dynamics (CFD) study was conducted showing 10-fold reduction in velocity magnitudes, wall shear stress and vorticity. This paper will report the results from the in-vitro PIV study and the mathematical modeling (CFD study).   The authors will also discuss a co-relationship between in-vitro PIV study results and results from the mathematical modeling with in-vivo patient angiography.