Repeated unit cell (RUC) approach for pure bending analysis of coronary stents.

Flexibility is one of the key properties of coronary stents. The objective of this paper is to characterize the bending behaviour of stents through finite element analysis with repeated unit cell (RUC) models. General periodic boundary conditions for the RUC under the pure bending condition are formulated. It is found that the proposed RUC approach can provide accurate numerical results of bending behaviour of stents with much less computational costs. Bending stiffness, post-yield bending behaviour and the relationship between moment and bending curvature are investigated for Palmaz-Schatz stents and stents with the V- and S-shaped links. It is found that the effect of link geometry on the bending behaviour of stent is significant. The behaviour of stents subjected to cyclic bending is also investigated.

On the finite element modelling of balloon-expandable stents.

Finite element method (FEM) has been extensively applied in the analyses of mechanical and biomechanical properties of stents. Geometrically, a closed-cell stent is an assembly of a number of repeated unit cells and exhibits periodicity in both longitudinal and circumferential directions. The objective of this paper is to study the FEM models for the analysis of stents. To this end, three models, termed respectively as the Panel, RUC (repeated unit cell) and RUC(+) (repeated unit cell with a free end) models, are proposed incorporating rotationally symmetrical, periodic and free edge conditions. The proposed models are applied to the analysis of stents of Palmaz-Schatz and sinusoidal types. The Panel model reduces the size of the numerical model from the full, half or quarter stent to a strip of it without losing the computational accuracy. The RUC model gives satisfactory results for the inner part of the stent except for the two ends. The RUC(+) model, described here for the first time, provides accurate results for both the inner part and the distal ends of the stent. In addition, it allows the prediction of the well-known phenomenon of "dog-boning", in which the balloon is excessively expanded at the two ends of the stent.