Multi-Objective Design of a Biodegradable Coronary Artery Stent - Cardiovascular and Cardiac Therapeutic Devices - page 20

Fig. 15 Response surface model for non-dimensional flexibility. See caption for Fig. 12

needed to modify the associated simulation models for the study of the biode-
gradable scaffold. The design concept is the subject of an ongoing patent appli-
cation, so specific details cannot be provided here. Nonetheless, it can be revealed
that four design parameters were used including strut width and one related to the
shape of the crowns. The strut thickness was fixed at 150 lm. Despite the lack of
detail, this test case provides valuable insight to a real coronary artery design
problem.
A 78 % symmetric constriction was used, comprising a Neo-Hookean repre-
sentation of the single constituent plaque, inside a single layer of arterial tissue,
similar to the setup described in Sect. 4.3 . Although symmetry is exploited here for
the demonstration purposes, in reality most coronary plaques are eccentric. Each
CAD scaffold model was imported into an Abaqus assembly and placed inside the
constriction (i.e. no stent positioning step was needed). Then, using Abaqus
Explicit 6.9-1, separate steps were performed to simulate crimping onto a balloon-
catheter followed by balloon expansion. In both steps, loading and relaxation were
included using a smooth step profile. At the end of each simulation, metrics were
extracted for the minimum lumen area (MLA) and the average recoil. A third
measure of performance was obtained for the predicted drug distribution by run-
ning the steady state heat diffusion analogue in Abaqus Standard 6.9.1. Finally, a
separate simulation was performed on the crimped stent (again in Abaqus Standard
6.9.1) to extract a fourth metric for the flexibility. Further details concerning the
setup of these simulations are available in [ 25 ].