Application of the penalty coupling method for the analysis of blood vessels

Due to the significant health and economic impact of blood vessel diseases on modern society, its analysis is becoming of increasing importance for the medical sciences. The complexity of the vascular system, its dynamics and material characteristics all make it an ideal candidate for analysis through fluid structure interaction (FSI) simulations. FSI is a relatively new approach in numerical analysis and enables the multi-physical analysis of problems, yielding a higher accuracy of results than could be possible when using a single physics code to analyse the same category of problems. This paper introduces the concepts behind the Arbitrary Lagrangian Eulerian (ALE) formulation using the penalty coupling method. It moves on to present a validation case and compares it to available simulation results from the literature using a different FSI method. Results were found to correspond well to the comparison case as well as basic theory

Sequential Structural and Fluid Dynamics Analysis of Balloon-Expandable Coronary Stents: A Multivariable Statistical Analysis

Several clinical studies have identified a strong correlation between neointimal hyperplasia following coronary stent deployment and both stent-induced arterial injury and altered vessel hemodynamics. As such, the sequential structural and fluid dynamics analysis of balloon-expandable stent deployment should provide a comprehensive indication of stent performance. Despite this observation, very few numerical studies of balloon-expandable coronary stents have considered both the mechanical and hemodynamic impact of stent deployment. Furthermore, in the few studies that have considered both phenomena, only a small number of stents have been considered. In this study, a sequential structural and fluid dynamics analysis methodology was employed to compare both the mechanical and hemodynamic impact of six balloon-expandable coronary stents. To investigate the relationship between stent design and performance, several common stent design properties were then identified and the dependence between these properties and both the mechanical and hemodynamic variables of interest was evaluated using statistical measures of correlation. Following the completion of the numerical analyses, stent strut thickness was identified as the only common design property that demonstrated a strong dependence with either the mean equivalent stress predicted in the artery wall or the mean relative residence time predicted on the luminal surface of the artery. These results corroborate the findings of the large-scale ISAR-STEREO clinical studies and highlight the crucial role of strut thickness in coronary stent design. The sequential structural and fluid dynamics analysis methodology and the multivariable statistical treatment of the results described in this study should prove useful in the design of future balloon-expandable coronary stents

A study of balloon type, system constraint and artery constitutive model used in finite element simulation of stent deployment

This work is made available according to the conditions of the Creative Commons Attribution 4.0 International (CC BY 4.0) licence. Full details of this licence are available at: https://creativecommons.org/licenses/by/4.0/This paper carried out a comparative study of different practices used in finite element simulation of stent deployment, with a focus on the choice of balloon type, system constraint and artery constitutive model. Folded balloon produces sustained stent expansion under a lower pressure when compared to rubber balloon. The maximum stresses on the stent and stenotic artery are considerably higher for simulations using a folded balloon, due to the assumed elastic behaviour of the folded balloon which signified the contact stresses between the balloon and the stent. The achieved final diameter is larger for folded balloon than that for rubber balloon, with increased dogboning and decreased recoiling effects. Fully constrained artery reduces the final expansion when compared to a free artery and a partially constrained artery due to the increased recoiling effect. The stress on the plaque-artery system has similar distribution for all three types of artery constraints (full, partial and free of constraints), but the magnitude is higher for a free artery as a result of more severe stretch. Stenotic plaque model plays a dominant role in controlling stent expansion, and calcified plaque model leads to a considerably lower expansion than hypocellular plaque model. Simulations using Ogden and 6-parameter polynomial models generate different behaviour for stent expansion. For Ogden model, stent expansion approaches the saturation at a certain stage of balloon inflation, while saturation is not observed for 6- 2 parameter polynomial model due to the negligence of the second stretch invariant in the strain energy potential. The use of anisotropic model for the vessel layers reduced the expansion at peak pressure when compared to the simulation using an isotropic model, but the final diameter increased due to the significantly reduced recoiling effect. The stress distribution in the arteryplaque system is also different for different combination of artery and plaque constitutive models. In conclusion, folded balloon should be used in the simulation of stent deployment, with the artery partially constrained using spring elements with a proper stiffness constant. The blood vessel should be modelled as a three-layer structure using a hyperelastic potential that considers both the first and second stretch invariants as well as the anisotropy. The composition of the plaque also has to be considered due to its major effect on stent deployment