Stacey R. Froemming

Finite Element Analysis of the Implantation of a Self-Expanding Stent: Impact of Lesion Calcification

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Performance of Self-Expanding Nitinol Stent in a Curved Artery: Impact of Stent Length and Deployment Orientation

The primary aim of this work was to investigate the performance of self-expanding Nitinol stents in a curved artery through finite element analysis. The interaction between a PROTÉGÉ™ GPS™ self-expanding Nitinol stent and a stenosed artery, as well as a sheath, was characterized in terms of acute lumen gain, stent underexpansion, incomplete stent apposition, and tissue prolapse. The clinical implications of these parameters were discussed. The impact of stent deployment orientation and the stent length on the arterial wall stress distribution were evaluated. It was found that the maximum principal stress increased by 17.46%, when the deployment orientation of stent was varied at a 5 deg angle. A longer stent led to an increased contact pressure between stent and underlying tissue, which might alleviate the stent migration. However, it also caused a severe hinge effect and arterial stress concentration correspondingly, which might aggravate neointimal hyperplasia. The fundamental understanding of the behavior of a self-expanding stent and its clinical implications will facilitate a better device design.

ARTERIAL WALL MECHANICS AND CLINICAL IMPLICATIONS AFTER CORONARY STENTING: COMPARISONS OF THREE STENT DESIGNS

The goal of this work is to quantitatively assess the relationship between the reported restenosis rates and stent induced arterial stress or strain parameters through finite element method. The impact of three stent designs (Palmaz–Schatz stent, Express stent, and Multilink Vision stent) on the arterial stress distributions were characterized. The influences of initial stent deployment location, stent-tissue friction, and plaque properties on the arterial stresses were also investigated. Higher arterial stresses were observed at the proximal end of the plaque. The Multilink–Vision stent induced lesser stress concentrations due to the high stiffness of the Cobalt Chromium material and thinner strut thickness. The stentinduced arterial stress concentrations were positively correlated with the reported in-stent restenosis rates, with a correlation coefficient of 0.992. Stent deployment initiated at the center of the lumen led to less arterial stress variation, while deployment closer to the thinner edge of the plaque causes higher arterial stresses. The friction between the stent and tissue was found to contribute to larger stress alternations for the plaque only. Increased plaque stiffness resulted in a reduced arterial stress concentration and clinical restenosis rate. Results presented herein suggested that arterial stresses serve as a comprehensive index factor to predict the occurrence of in-stent restenosis, which will facilitate the new stent design and surgical planning.

On the Importance of Modeling Stent Procedure for Predicting Arterial Mechanics

The stent-artery interactions have been increasingly studied using the finite element method for better understanding of the biomechanical environment changes on the artery and its implications. However, the deployment of balloon-expandable stents was generally simplified without considering the balloon-stent interactions, the initial crimping process of the stent, its overexpansion routinely used in the clinical practice, or its recoil process. In this work, the stenting procedure was mimicked by incorporating all the above-mentioned simplifications. The impact of various simplifications on the stent-induced arterial stresses was systematically investigated. The plastic strain history of stent and its resulted geometrical variations, as well as arterial mechanics were quantified and compared. Results showed the model without considering the stent crimping process underestimating the minimum stent diameter by 17.2%, and overestimating the maximum radial recoil by 144%. It was also suggested that overexpansion resulted in a larger stent diameter, but a greater radial recoil ratio and larger intimal area with high stress were also obtained along with the increase in degree of overexpansion.

Experimental investigation of the stent-artery interaction

Abstract It is well acknowledged that stent implantation causes abnormal stretch and strains on the arterial wall, which contribute to the formation and progression of restenosis. However, the experimental characterization of the strain field on the stented vessel is scant. In this work, the balloon-expandable stent implantation inside an artery analogue was captured through two high-speed CCD cameras. The surface strain maps on the stented tube were quantified with a 3-D digital image correlation technique. The strain history at one specific reference point illustrated three stenting phases, including balloon inflation, pressurization and deflation. The surface strain distributions along one axial path were obtained at various time points to demonstrate the stent–vessel interactions. The radial wall thickness reduction history was used to evaluate the pressure–diameter relationship for the balloon. Results indicated that the expansion process of the balloon was significantly altered by the external loadings from both the stent and artery analogue. In addition, the repeatability of the stenting experiments was demonstrated through two tests with a change of 5% in the stent-induced maximum first principal strain. Moreover, a computational model of the stenting procedure was developed to recapture the stenting experiments. Comparison between experiments and simulation showed a difference of 7.17% in the first principal strain averaged over the high strain area. This indicated the validation of the computational framework, which can be used to investigate the strain or stress field throughout the computational domain, a feature that is not affected by experimental techniques.