PSI - Issue 15

Ran He et al. / Procedia Structural Integrity 15 (2019) 28–32 He et al. / Structural Integrity Procedia 00 (2019) 000–000

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1. Introduction In most of the computational studies, the plaque and artery were assumed to be uniform throughout, which is not the case in reality. It is of interest to explore the stenting-caused deformation to a non-uniform artery and to relate the computational studies to clinical situations. Some computational studies have been carried out to simulate stenting for specific patients. Mortier et al. (2010) compared the mechanical deformation of a left coronary artery bifurcation caused by the deployments of three different second-generation DESs. The internal surface of the 3D artery model was built based on a stack of images providing the centres, radii, and inclinations of vessel cross-sections; while the external surface was built by scaling the internal one. The arterial wall consisted of intima, media and adventitia layers, which were treated as anisotropic hyperelastic materials. Their results showed that the implantations of all three stents straightened the curved coronary bifurcation and induced stress concentrations in the arterial wall due to compliance mismatches at the ends of the stents. Morlacchi et al. (2013) simulated stenting procedures based on two clinical cases. The internal surfaces of two left anterior descending coronary arteries were reconstructed from the scanned images, while the external ones followed the centrelines with assumed diameters. The model had only two layers, i.e., the arterial wall and the plaque, both assumed to be isotropic hyperelastic materials. They observed the straightening of the arterial wall caused by the stent implantation and higher stresses in both the artery and the stents due to stent overlapping. Ragkousis et al. (2014) simulated the deployment of four different DES designs in a patient-specific right coronary artery. The internal and external surfaces of the artery were both created from angiographic images, however the wall was assumed to be isotropic hyperelastic with only one layer. The stents showed significantly different longitudinal strength as seen from mechanical testing; however, their longitudinal stabilities predicted by simulations were different from experimental results. In the existing studies, either the model did not consider the arterial layers/plaque or the tissues were assumed to be isotropic. Hence, in this paper, stent deployment in a patient-specific coronary artery is investigated using a finite-element (FE) method, with the consideration of vessel layers, plaque and their anisotropic properties. The model is built based on data of an actual patient. FE simulations are carried out for stenting procedure to obtain its lumen gain, in comparison with the clinical results. 2. Finite element simulations 2.1. Models of artery, plaque, stent, and balloon The artery-plaque model was developed by using Mimics with a length of 30 mm. Based on intravital optical coherency tomography imaging of a specific patient’s coronary artery, the inner surface of the diseased arterial wall was built. The diameter of the interface between the plaque and the media, i.e., the reference diameter, was measured as 4 mm. The overall thickness of arterial wall was 0.66 mm, including 0.34 mm adventitia layer and 0.32 mm media layer (Holzapfel et al., 2005). Tetrahedral elements (C3D4) were used to mesh the plaque and the artery by 3-Matics. The off-the-shelf Resolute Integrity™ drug-eluting stent had a length of 12 mm and an outer diameter of 2.75 mm. The tri-folded balloon had a length of 16 mm and a fully inflated diameter of 3 mm. Both stent and balloon models were created and meshed using Abaqus. C3D8R hexahedral brick elements with reduced integration and M3D4R three-dimensional 4-node membrane elements with reduced integration were used to mesh the stent and the balloon, respectively. The stent-balloon assembly was crimped by 12 rigid plates before introduced into the artery-plaque assembly. Fig. 1 shows the artery-plaque-stent-balloon assembly used for simulation of stent deployment.