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Three representative stents. Top: Palmaz–Schatz (PS) stent. Middle: Express stent. Bottom: Multilink–Vision stent.
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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...
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... implantation is one of the most common minimally invasive treat- ments for opening the obstructed coronary artery. The increase in the popu- larity of stenting as a primary treatment and extension of stenting techniques to more complex lesion types has prompted innovative and competitive stent designs [Oesterle et al. , 1998; Colombo et al. , 2002;Mackerle, 2005]. A stent is a mesh structure used to restore the patency in stenosed arteries and provide a permanent scaffold for arterial walls. The permanent implanted stent subjects the artery to abnormal stresses which may lead to the occurrence of in-stent re- stenosis, a major complication of stenting [Oesterle et al. , 1998]. Clinical trials have reported various restenosis rates on different stent designs [Becker, 1991; Oesterle et al. , 1998; Schwartz et al. , 1999; Squire et al. , 1999; Kastrati et al. , 2000; Palmaz, 2002; Steinman et al. , 2003]. Morton has performed a clinical review on the impact of a plethora of physical stent parameters, such as the stent length, diameter, percent metal coverage, strut density, strut thickness, surface quality, cross-section shape, symmetry of deployment, and stent material [Morton et al. , 2004]. It is speculated that considerable strain on the vessel wall imposed by the stent or the balloon of the catheter on the endothelium have caused the produc- tion of smooth muscle cell abundance and fibroblast growth factors, which led to the restenosis. Understanding the impact of mechanical factors on the arte- rial injury is essential to develop strategies to prevent and treat a major source of stent failure like restenosis. Finite element analysis has been proven to be a useful and efficient tool for the study of stent expansion, the interaction between the stent and catheter bal- loon, and stent-plaque-artery interactions. Cui et al. studied the influence of bal- loon length and compliance on the mechanical behaviors of expanded stent, such as foreshortening, dogboning and stent recoil [Cui et al. , 2010]. De Beule has sum- marized the computational modeling of balloon-expandable stents, which did not include the interaction between the stent and balloon [De Beule, 2009]. Au- ricchio et al. studied the biomechanical interaction between a stent and a stenosed artery [Auricchio et al. , 2001]. Wang et al. examined the stresses in the artery wall near the ends of the stent [Wang et al. , 2006]. Bedoya et al. suggested that stents with small strut spacing (the link between two struts), zero radius of curvature at the end of links will cause high stresses over larger areas of the artery [Bedoya et al. , 2006]. According to the best available data, the effects of friction and stent de- ployment location have not been reported in the numerical studies. Quantitative correlation between arterial stress parameters with the occurrence of in-stent re- stenosis is also lacking. In this work, stress distributions on the arterial wall was determined and the clinical implications associated with stenting was investigated by testing the hy- pothesis that different stent designs will provoke different level of stress con- centration in the artery, which are correlated with the occurrence rate of in- stent restenosis. Three commercially available balloon expandable stent designs (Palmaz–Schatz stent, Express stent, and Multilink–Vision stent) were modeled to compare mechanical characteristics of stented arteries using the commercial software ABAQUS (Dassault Syst`emes Simulia Corp., Providence, RI, USA). The impact of friction between stent and tissue was evaluated. The stent deployment location inside the lumen was investigated to estimate the influence of the clini- cal operator. Three stages of plaques (Cellular, Hypo-cellular, and Calcified) were also used to assess the significance of the material properties. A segment of proximal left anterior descending coronary artery (LAD) before the origin of the first septal branch is studied, which is represented by a straight cylinder with a 3mm lumen diameter and a length of 26mm. The thickness of the artery is assumed as 1/4th of the lumen, i.e., 0.75mm. The asymmetric plaque has a parabolic longitudinal profile (Figure 1). An edge ratio of 2:1 at the narrowest lumen leads to a remaining lumen diameter of 50% of the reference lumen, which is referred to as 50% stenosis. The longitudi- nal length of the plaque is 13 mm. Both the plaque and artery are expanded to the reference lumen size of 3 mm by three types of stents (Figure 2). The physical pa- rameters and restenosis rates for these stents are summarized in Table 1. The metallic stents are modeled as perfect linear elastic-plastic materials. The material properties for 316LN stainless steel are as follows: Young’s modulus E = 190GPa; Poisson ratio ν = 0 . 3; Yield stress σ Y = 207 MPa; Limit stress σ M = 515 MPa; Limit nominal strain ε M = 60%. The plastic behavior of stents is modeled assuming isotropic hardening, which was validated by Auricchio et al. [2001]. The material properties for L605 Cobalt Chromium alloy are as follows: Young’s modulus E = 243 GPa; Poisson ratio ν = 0 . 3; Yield stress σ Y = 500 MPa; Limit stress σ M = 1000 MPa [Poncin et al. , 2004]. Both artery and plaque are defined by a hyperelastic isotropic constitutive model. The 3rd-order polynomial form of the strain energy density function U is used in this ...
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The haemodynamic behaviour of blood inside a coronary artery after stenting is greatly affected by individual stent features as well as complex geometrical properties of the artery including tortuosity and curvature. Regions at higher risk of restenosis, as measured by low wall shear stress (WSS < 0.5 Pa), have not yet been studied in detail in cur...
Citations
... The mechanical behavior of a stent under various loading conditions, such as tensile, compression, bending, and crushing, plays a vital role in the functionality of the stent, including structural support, blood flow adjustments, drug delivery efficiency improvement, and so forth. The ideal stent would be one that can reopen narrowed vessels with large radius expanding deformation, have high radial strength [5] for good arterial support post-expansion, adequate flexibility [10], biocompatibility, biodegradability, cause minimal injury to the artery in an expanded state, and result in a small amount of axial recoil for minimal shear damage [11,12]. Additionally, there is inevitably a trade-off between radial strength and bending flexibility in stent design [10]. ...
... The tests gave the average maximum static CoF along the helix µ sa,∥ = 0.12, the average maximum static CoF perpendicular to the helix µ sa,⊥ = 0.18, the average kinetic CoF along the helix µ ka,∥ = 0.07, the average kinetic CoF perpendicular to the helix µ ka,⊥ = 0.08. The measurements on kinetic CoF align with the reported values in the literature, where the CoF between stent devices and the endothelial cells of artery lumens could vary from 0.03 to 0.06 68 . ...
Microcatheters have enabled diverse minimally invasive endovascular operations and notable health benefits compared with open surgeries. However, with tortuous routes far from the arterial puncture site, the distal vascular regions remain challenging for safe catheter access. Therefore, we propose a wireless stent-shaped magnetic soft robot to be deployed, actively navigated, used for medical functions, and retrieved in the example M4 segment of the middle cerebral artery. We investigate shape-adaptively controlled locomotion in phantoms emulating the physiological conditions here, where the lumen diameter shrinks from 1.5 mm to 1 mm, the radius of curvature of the tortuous lumen gets as small as 3 mm, the lumen bifurcation angle goes up to 120°, and the pulsatile flow speed reaches up to 26 cm/s. The robot can also withstand the flow when the magnetic actuation is turned off. These locomotion capabilities are confirmed in porcine arteries ex vivo. Furthermore, variants of the robot could release the tissue plasminogen activator on-demand locally for thrombolysis and function as flow diverters, initiating promising therapies towards acute ischemic stroke, aneurysm, arteriovenous malformation, dural arteriovenous fistulas, and brain tumors. These functions should facilitate the robot’s usage in new distal endovascular operations.
... A patch-conforming method was used to generate the mesh with an average mesh density of 200,000 elements after sensitivity testing. L-605 Cobalt-Chromium was used as the material, with a Young's modulus of 243 GPa, density of 9100 kg∕m 3 , tensile strength of 1000 MPa and yield stress of 500 MPa (Gu et al., 2012). ...
Stents are scaffolding cardiovascular implants used to restore blood flow in narrowed arteries. However, the presence of the stent alters local blood flow and shear stresses on the surrounding arterial wall, which can cause adverse tissue responses and increase the risk of adverse outcomes. There is a need for optimization of stent designs for hemodynamic performance. We used multi-objective optimization to identify ideal combinations of design variables by assessing potential trade-offs based on common hemodynamic indices associated with clinical risk and mechanical performance of the stents. We studied seven design variables including strut cross-section, strut dimension, strut angle, cell alignment, cell height, connector type and connector arrangement. Optimization objectives were the percentage of vessel area exposed to adversely low time averaged WSS (TAWSS) and adversely high Wall Shear Stress (WSS) assessed using computational fluid dynamics modeling, as well as radial stiffness of the stent using FEA simulation. Two multi-objective optimization algorithms were used and compared to iteratively predict ideal designs. Out of 50 designs, three best designs with respect to each of the three objectives, and two designs in regard to overall performance were identified.
... Although the literature concerning the modeling of the stent deployment into a stenosed artery is rich in terms of stent design and deformation [Gu et al., 2012;Wang et al., 2012;Liu et al., 2020], material of the stent and its constitutive model [Liu et al., 2019], the majority of the studies employed a rather simple cylindrical shape for the artery [Cui et al., 2010;Kai et al., 2020]. Some studies focused on more realistic geometries of the stenosed artery [Holzapfel et al., 2005;Voß et al., 2019] and investigated the effects of stent insertion or blood flow on the artery. ...
... Some studies focused on more realistic geometries of the stenosed artery [Holzapfel et al., 2005;Voß et al., 2019] and investigated the effects of stent insertion or blood flow on the artery. However, these studies employed hyperelastic constitutive models for the arterial tissues which are not enough for supra-physiological loading that occurs during stent deployment [Gu et al., 2012;Mozafari et al., 2018;Ruan et al., 2018]. In supraphysiological loading inelastic phenomena such as stress softening and permanent deformation may occur in arterial tissues [Maher et al., 2012;Fereidoonnezhad et al., 2016]. ...
Computational models provide a powerful tool for pre-clinical assessment of medical devices and early evaluation of potential risks to the patient in terms of plaque fragmentation and in-stent restenosis (ISR). Using a suitable constitutive model for arterial tissue is key for the development of a reliable computational model. Although some inelastic phenomena such as stress softening and permanent deformation likely occur due to the supra-physiological loading of arterial tissue during the stenting procedure, hyperelastic constitutive models have been employed in most of the previously developed computational models. This study presents a finite element model for stent deployment into a patient-specific stenosed artery while inelastic arterial behaviors due to supra-physiological loading of the tissue have been considered. Specifically, the maximum stress in the plaque and the arterial layers which is the main cause of plaque fracture during stent deployment and the surgically-induced injury (damage) in the arterial wall, as the main cause of ISR, are presented. The results are compared with the commonly-used hyperelastic behavior for arterial layers. Furthermore, the effects of arterial material parameter variation, analogues to different patients, are investigated. A higher amount of damage is predicted for the artery which shows a higher stress in a specific strain.
... Computational modeling of the stenting procedure provides a powerful tool for an early evaluation of the potential risk of a specific stent for the patient in terms of (i) vessel wall damage, as the main cause of ISR, and (ii) plaque fragmentation which can cause a downstream occlusion of tiny blood vessels. Although the literature concerning the modeling of the stent deployment into a stenosed artery is rich in terms of stent design and deformation (Gu et al, 2012;Wang et al., 2012;Liu et al., 2020), material of the stent and its constitutive model (Liu et al., 2019), the majority of the studies employed a rather simple cylindrical shape for the artery (Rivlin and A, 2006;Cui et al., 2010, Kai et al., 2020. Some studies focused on more realistic geometries of the stenosed artery (Holzapfel, 2005;Voß et al., 2019) and investigated the effects of stent insertion or blood flow on the artery. ...
Although some inelastic phenomena such as stress softening and permanent deformation likely occur due to the supra-physiological loading of arterial tissue during the stenting procedure, hyperelastic constitutive models have been employed in most of the previously developed computational models. This study presents a finite element model for stent deployment into a patient-specific stenosed artery while inelastic arterial behaviors due to supra-physiological loading of the tissue have been considered.
... In this section, a self-expanding stent is used as the optimization case study. Stent implantation is one of the most effective minimally invasive treatments for the obstruction of coronary arteries [11]. Based on different deployment approaches, stents can be classified as two types: balloon-mounted and self-expanding stents. ...
This paper presents an efficient structural optimization approach for shape memory alloys (SMAs) with respect to fatigue. In the proposed method, a nonparametric shape optimization approach based on optimality criteria is applied to change the structural configuration. The design optimization framework is accomplished by relying on commercially available software and tools. In addition, both low- and high-cycle fatigue criteria are used to compute the fatigue factor at each material point, indicating its degree of safeness with respect to fatigue. Meanwhile, a 3D constitutive model is utilized to predict, with good accuracy, the stabilized thermomechanical stress state of a SMA structure subjected to multiaxial nonproportional cyclic loading. Finally, numerical examples are tested to demonstrate the effectiveness of the proposed method.
... The automated results could be input into finite element models to predict the clinical outcomes of using stents in certain lesions. 47,48 Thus, from A-line segmentation results, we have an opportunity to give recommendations on proper stent sizing, location, and potential plaque modifications. Moreover, the software provides an opportunity for offline assessment of drug and biologic therapeutics. ...
We developed machine learning methods to identify fibrolipidic and fibrocalcific A-lines in intravascular optical coherence tomography (IVOCT) images using a comprehensive set of handcrafted features. We incorporated features developed in previous studies (e.g., optical attenuation and A-line peaks). In addition, we included vascular lumen morphology and three-dimensional (3-D) digital edge and texture features. Classification methods were developed using expansive datasets (∼7000 images), consisting of both clinical in-vivo images and an ex-vivo dataset, which was validated using 3-D cryo-imaging/histology. Conditional random field was used to perform 3-D classification noise cleaning of classification results. We tested various multiclass approaches, classifiers, and feature selection schemes and found that a three-class support vector machine with minimal-redundancy-maximal-relevance feature selection gave the best performance. We found that inclusion of our morphological and 3-D features improved overall classification accuracy. On a held-out test set consisting of >1700 images, we obtained an overall accuracy of 81.58%, with the following (sensitivity/specificity) for each class: other (81.43/89.59), fibrolipidic (94.48/87.32), and fibrocalcific (74.82/95.28). The en-face views of classification results showed that automated classification easily captured the preponderance of a disease segment (e.g., a calcified segment had large regions of fibrocalcific classifications). Finally, we demonstrated proof-of-concept for streamlining A-line classification output with existing fibrolipidic and fibrocalcific boundary segmentation methods, to enable fully automated plaque quantification. The results suggest that our classification approach is a viable step toward fully automated IVOCT plaque classification and segmentation for live-time treatment planning and for offline assessment of drug and biologic therapeutics.
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... A review with a thorough description of the general characteristics of an "ideal" stent and different components of stent design was summarized as: trackable, radio-opaque, thromboresistant, biocompatible, reliably expandable, high radial strength, circumferential coverage, low surface area, hydrodynamic compatibility and so on [Sangiorgi et al., 2007]. Different types of stent are of great importance in the treatment of vascular disease [Kastrati et al., 2001;Gu et al., 2012]. ...
Chiral and reentrant metastructures with auxetic deformation abilities can serve as the building blocks in many industrial applications because of their light weight, high specific strength, energy absorption properties. In this paper, we report an innovative tubular-like structure by a combined mechanical effect of antichiral and reentrant. 2D antichiral-reentrant hybrid structures consisting of circular nodes and tangentially-connected ligaments are predesigned and fabricated using laser cutting technology with high-resolution. The elastic properties and auxeticity of the plane structure are analyzed and compared based on finite element analysis (FEA) and experimental results. For the first time, the antichiral-reentrant hybrid intravascular stents with the auxetic feature are proposed and parametric models are devised with good geometrical structure demonstrated. A series of large-scale stents are manufactured with stereolithography apparatus (SLA) additive manufacturing technique, and their mechanical behaviors are investigated in both experimental tests and FEA. As the selected antichiral-reentrant hybrid stents with tailored expansion ability are subjected to radial loading by the dilation of the balloon, stents undergo identifiable deformation mechanism due to the beam-like ligaments and circular node elements in the varied geometrical design, resulting in the distinct stress outcomes in plaque. It is also demonstrated that the antichiral-reentrant hybrid stents with tunable auxeticity possess robust mechanical properties through implantation inside the obstructed lesion.
... More ac- curate modeling can be achieved by including non-linear elasticity of arterial walls. In [45,46], the authors try to quantify the friction between an implanted stent and the inner- most arterial wall and conclude that a coefficient of 0.03 -0.06 adequately represents the frictional force. This is something worth investigating-specifically the relationship be- tween harvested power and the frictional coefficient which will be essential for optimizing the harvested power. ...
This manuscript investigates energy harvesting from arterial blood pressure via the piezoelectric effect for the purpose of powering embedded micro-sensors in the human brain. One of the major hurdles in recording and measuring electrical data in the human nervous system is the lack of implantable and long term interfaces that record neural activity for extended periods of time. Recently, some authors have proposed micro sensors implanted deep in the brain that measure local electrical and physiological data which is then communicated to an external interrogator. This paper proposes a way of powering such interfaces. The geometry of the proposed harvester consists of a piezoelectric, circular, curved bimorph that fits into the blood vessel (specifically, the Carotid artery) and undergoes bending motion because of blood pressure variation. In addition, the harvester thickness is constrained such that it does not modify arterial wall dynamics. This transforms the problem into a known strain problem and the integral form of Gauss’s law is used to obtain an equation relating arterial wall motion to the induced voltage. The theoretical model is validated by means of a Multiphysics 3D-FEA simulation comparing the harvested power at different load resistances. The peak harvested power achieved for the Carotid artery (proximal to Brain), with PZT-5H, was 11.7 μ W. The peak power for the Aorta was 203.4 μ W. Further, the variation of harvested power with variation in harvester width and thickness, arterial contractility and the pulse rate is investigated. Moreover, potential application of the harvester as a chronic, implantable and real-time Blood pressure sensor is considered. Energy harvested via this mechanism will also have applications in long-term, implantable Brain Micro-stimulation.
... Prevalent stents have numerous design patterns, the widespread interest focused on the properties of stent designs in terms of multiple types geometry [1,5,6]. The elevated stress region largely depends on the strut shape of stents in terms of mechanical stress corresponding to the clinical observations [12,13]. The results from this study show that the strut length, separation angle and cell asymmetry are crucial to the performance of stent design. ...
