Constitutive Modeling and Numerical Simulation of Coronary Arteries Mechanical Behavior in Stenting and Succeeding Growth

Fereidoonnezhad, Behrooz | 2017

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  1. Type of Document: Ph.D. Dissertation
  2. Language: English
  3. Document No: 50614 (58)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Science and Engineering
  6. Advisor(s): Naghdabadi, Reza; Sohrabpour, Saeed
  7. Abstract:
  8. Cardiovascular diseases are the major cause of death worldwide. Atherosclerosis is one of the major types of cardiovascular diseases in which fibrous and fatty materials, called plaque, build up inside the artery and cause partial or total occlusion of the artery. Intravascular balloon angioplasty with or without stenting is the most common treatment of this disease. In 2010, approximately 954000 stent implantations were performed in the United States. The major issue associated with stenting is reclosure or renarrowing of the transverse section of the artery termed in-stent restenosis (ISR). Unfortunately, nearly one–third of the patients
    who receive stent implantation require further intervention within 6 months to reopen the previously stented arteries. The mechanism of restenosis after balloon angioplasty is a combination of elastic recoil, arterial vessel remodeling,and neointimal hyperplasia. However, late lumen loss in stented segments of the artery is often the result of neointimal hyperplasia.This research deals with several aspects of the arterial wall mechanics after balloon angioplasty and stent deployment. Initially, we consider the inelastic behavior of the arterial wall in supra–physiological loadings. Employing the pseudo–elasticity theory, we present a constitutive model which considers stress softening (Mullin effects) and permanent deformation in arterial wall. Considering these inelastic phenomena is important in predicting the outcomes of clinical treatments such as balloon angioplasty with/without stenting and arterial clamping. Furthermore, the model has been implemented in a finite element code and numerically analyzed with respect to experimental tests, i.e. cyclic uniaxial tension in circumferential and longitudinal directions. The results show that the model is able to capture specific features of arterial wall behavior including anisotropy, nonlinearity, and damage-induced inelastic phenomena, i.e. stress softening and permanent deformation. Finite element results of a more complex vi boundary-value problem, i.e. aortic clamping considering the three aortic layers,residual stress, non-symmetric blood pressure after clamping, and patientspecific data are also presented.The second part of this dissertation deals with the mechanically–induced adaptive growth of arterial wall after balloon angioplasty and stent implantation which is known as the major cause of ISR. ISR is one of the main drawbacks of stent implementation which limits the long-term success of the procedure. Morphological changes occurring within the arterial wall due to stent–induced mechanical injury are a major cause for activation of vascular smooth muscle cells (VSMCs), and the subsequent development of ISR. Considering the theory of volumetric mass growth and adopting a multiplicative decomposition of the deformation gradient into an elastic part and a growth part, we present an isotropic mechanobiological model for ISR. An evolution equation is developed for mass growth of the neointima, in which the activation of VSMCs due to stent–induced
    damage (injury) and the proliferation rate of the activated cells are considered.By introducing the mass evolution into the mass balance equation, we obtain the evolution of the growth tensor over time. The model has been implemented in a finite element code and the procedure of angioplasty was simulated, whereby the features of the proposed growth model are illustrated. We extend the isotropic growth model to an anisotropic one in the last part of this dissertation. A semi–analytical solution for damage–induced anisotropic growth of an artery wall after balloon angioplasty and stenting is then conducted in which the residual stress is also considered. The model is then implemented in ABAQUS/STANDARD within the user-defined subroutine UMAT and the FE code is verified by comparing the FE results with the semi-analytical solution for the growth of artery wall.The work presented in this thesis has provided a better understanding of the mechanical and mechanobiological response of arterial wall to stent deployment and serves as a basis for future computational work in this field
  9. Keywords:
  10. Atherosclerosis ; Damage ; Growth ; Restenosis ; Mechanical Behavior ; Coronary Arteries ; Stent Implementation

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