PSI - Issue 15

Sharath Chavalla et al. / Procedia Structural Integrity 15 (2019) 8–15 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Unlike the stent geometry, which is generated by assembling number of patches, the artery was generated as a single geometrical entity. Hence the artery is essentially a single patch and the order of the NURBS patch of artery is maintained to be cubic along the surface direction and quadratic through the stent thickness. The carotid artery is an assembly of elastic lamellae, elastin-collagen fibers and collagen fibers. In a study constituted by Khamdaeng et al. (2012), it was determined that the elastin-collagen fiber network predominantly provides an elastic response. Based on this experimental work, we consider the artery as a linearly elastic isotropic material with a Young’s modulus of 1 MPa and a Poisson’s ratio of 0.4. 3.4. Stent deployment simulation The prior sections laid the basis for the development of NURBS models of the stent and the carotid artery that can be analyzed using IGA. In this section the simulation setup framework for the stent deployment is presented. During the stent deployment inside the artery, the stent is subjected to crimping, bending and expansion. The mentioned stages of stenting procedure are enabled by means of a cylinder model that encompasses the stent. The cylinder acts as a catheter which in reality is used for the stent deployment. The cylinder is considered as a rigid body in this study and is in the form of a trivariate NURBS patch, the order of which is similar to that of the stent patches and the artery model.

Fig. 2. (a) Point cloud of carotid artery in STL format; (b) skeletal geometry of carotid artery; (c) 3D NURBS carotid artery model.

All the simulation steps in the stenting simulation are driven using the displacement boundary conditions. Initially, the cylinder and the stent geometry come in contact with each other during the crimping simulation resulting in reduction of the stent radius. It is evident that the reduction of the radius results in elongation of the stent. In the current work we restrict the elongation of the stent only in one direction for simplicity. The crimped stent along with the cylinder is then subjected to bending such that they match the centerline of the carotid artery model. It should be noted that this is the ideal condition required during the clinical intervention. In the final step of the deployment, the cylinder is allowed to expand radially. This enables the crimped stent to expand freely and establish contact with the inner artery surface. The contact between the artery and stent models is achieved by switching the active contact surfaces between stent-cylinder to stent-artery models. The radius of the stent is designed to be slightly greater than the mean artery radius in order to exert a gentle force on the artery. 4. Results and discussion This section outlines the simulation results. As elucidated earlier, initially the stent along with the cylinder is