Design Method for Bare Metal Stents and Finite Element Simulation

The most reason for cardiovascular diseases are the intra-vessel deposition of plaque, cholesterol etc. which lead to thrombus formation, arterial blockage and stenosis. The modern treatment of such problem is the introduction of a graft in the place of the vessel embracement. Most of the grafts used are expanded by a catheter balloon. They remain the required diameter after deflation of the catheter. In this work an original method for design and tessellation of a stencil form, which forms the struts and bridges in a native way, is proposed. An advantage of this approach is the easier design of computer geometry and CNC programming for the cutting laser. A real stent, designed using this method and produced from stainless steel 316L, is studied for its mechanical behaviour during and after balloon expansion by using Finite Element Method (FEM) modelling. The geometry of the stent and stent struts is proposed by the Firma ISMA EOOD, Sofia, Bulgaria. The FEM calculations are performed by both ISMA EOOD and the authors as a part of the procedure for admission for sale of the device in the US market. Following parameters have been estimated using FEM, thus imitating the process of stent expansion: final diameter in the middle and at distal region, radial recoil, foreshortening, dogbonig and flexibility of the stent. The good coincidence of the simulation results with the test with real devices makes the FEM modelling a suitable and reliable method for pre-clinical investigations and prediction of the mechanical properties of the designed stents. The original form, suggested by the Firma ISMA EOOD, explains their good mechanical properties. This is a good demonstration of the advantages of the suggested method for stent geometry design.