Bending stiffness characterization of braided stent using spring-based theoretical formula

Flexibility is critical to the braided stent in curing vascular diseases, but there is no theoretical method to characterize its bending stiffness. In this paper, firstly based on the theory of mechanical spring, derivations of an explicit theoretical formula are made to calculate the bending stiffness of the braided stent. The formula does ignore the change of the braiding angle, which, according to a geometric analysis, can get neutralized and has rare effects on the result. Next, an experiment on a braided tube and numerical simulations on stents are conducted, which provide validations to the theoretical formula through comparisons of bending stiffness, stress distributions, and bending angle versus moment curves. Finally, a parametric analysis based on the formula is carried out. It finds that bending stiffness is mostly affected by the wire diameter, but a smaller braiding angle is the key to improving the bending flexibility while keeping a sufficient radial stiffness. It also finds that the formula is applicable to other braiding configurations, such as dual-layer and regular braiding stents. The formula provides theoretical foundations for the stiffness design of the braided stent and can simplify the design process.