Analyses and design of expansion mechanisms of balloon expandable vascular stents.

Vascular stents are expanded in blood vessels with lumens larger than their cardiac counterparts. Extreme radial expansion significantly reduces the expanded length of some designs, resulting in insufficient lesion coverage and inaccurate placement. It is hypothesized that expansion mechanisms of a balloon-expandable stent, driven by plastic hinges, are controlled by the cell topology. This hypothesis is first tested for stent expansion using kinematic and kinetic analyses, followed by more detailed finite element (FE) calculations. Three balloon-expandable stent designs are laser micro-machined for experimental verification of the length-diameter relations predicted by the analytical and FE models. It is found that stent designs with positive, negative, or zero foreshortening over expansion phase can be designed by tailoring unit cell geometries and hence obtain desired length-diameter and pressure-diameter characteristics.