Layout design of a bi-stable cardiovascular stent using topology optimization

We present a novel design concept for a bi-stable cardiovascular stent in which the device has two fully stable, unloaded configurations: a contracted configuration used for insertion and positioning of the device, and an expanded configuration intended to facilitate blood flow. Once the device is in place, a small trigger force applied in the radial direction induces snap-through, causing the device to snap into its expanded configuration. We model the mechanics of the stent structure using a neo-Hookean hyperelastic formulation, which is discretized using a uniform mesh of solid isoparametric finite elements. Topology optimization is used to obtain the material layout and to tailor the nonlinear response of the baseline structure to achieve bi-stable snap-through behavior. The design domain is defined as a two-dimensional unit cell within the larger mesh pattern that comprises the cylindrical stent structure. We further introduce a novel transverse bracing system, which exerts a containing force that allows snap-through to occur, and that also ensures that the length of the stent does not change due to radial expansion. Optimization results are presented for several two dimensional examples including a benchmark problem based on a bi-stable beam, and a two-dimensional stent patch. Results confirm that topology optimization has been used successfully to achieve bi-stability in both the beam and the stent structures.