Mechanical characterization of braided self-expanding stents: Impact of design parameters

In this paper, the mechanical performance of braided nitinol stents was systematically studied to provide guidelines for optimum stent designs. The influences of braiding patterns, braiding angles, wire diameters, and strand numbers on the mechanical behavior of the stent in terms of crimping strain, radial strength, longitudinal flexibility, and stability were characterized utilizing finite element method. Our results have shown that the two key design factors of braided stents are the braiding angle and wire diameter. A smaller braiding angle can increase radial stiffness and have better longitudinal flexibility and can maintain the stent stability. The wire diameter has less influence on the radial stiffness than the braiding angle, but the longitudinal flexibility is most sensitive to the wire diameter. The strand number is directly proportional to the radial stiffness and inversely proportional to the longitudinal flexibility. Compared to the classical crossing pattern, we have also proposed two patterns. These patterns have a minimal impact on the crimping and radial stiffness of stents, but the stent made from them are more flexible. Among three crossing patterns, it is interesting to see that the classical pattern is the most stable crossing pattern for stand numbers larger than 36, but it became the most unstable pattern at the strand number of 24. This work has shed light on the optimum design of braided stents.