Stent design parameters and crimpability

Intravascular stenting is the leading treatment procedure for atherosclerotic coronary heart diseases. Among the various procedures, it is simpler and faster with a high initial success rate. Stent design, stent material, and clinical procedure decide the efficacy and life of stents. Strut thickness and crown radius are two essential design parameters that dictate expansion characteristics of stents. This research work discusses computational analysis of a specific stent, to explore the influence of thickness of strut on the deployment characteristics like stress/strain, foreshortening, recoil, and dog boning. The optimum stent design is one which gives maximum expansion with minimum stress distribution, dogboning, and elastic recoil. Five similar stent models with thickness ranges from 65μ to 105µ were modeled and computational method was adopted to simulate the transitory expansion nature of stent/balloon system. The FE results were substantiated with an in-vitro experiment. It was found that strut thickness has a major impact on stent recoil and low impact on foreshortening and dogboning. Foreshortening per unit expansion was almost same for entire models. Strut thickness 70μ to 80μ gives better expansion characteristics for the model under study.

Download Full-text

Effect of Stent Design Parameters on Coronary Artery Flow

ASME 2009 Summer Bioengineering Conference, Parts A and B ◽

10.1115/sbc2009-206569 ◽

2009 ◽

Author(s):

Satyaprakash Karri ◽

Stephen Peter ◽

Pavlos P. Vlachos

Keyword(s):

Thrombus Formation ◽

Design Parameters ◽

Radius Of Curvature ◽

Stent Design ◽

Endovascular Stents ◽

Long Term Performance ◽

Artery Flow ◽

Term Performance ◽

Realistic Geometries

The most widely accepted modality for treating diseased arteries is the implantation of endovascular stents. Stents are metallic wireframe devices used to reopen clogged arteries. Despite their widespread use, problems persist post-implantation of these devices beginning with sub-acute thrombus formation followed by inflammation, proliferation and remodeling [1]. The specific stent design and its design parameters profoundly impact the hemodynamic environment of the stent [2], in turn affecting thrombus accumulation between struts and thus restenosis [3]. Prior research examining the hemodynamic effects of stents has been performed in simplified geometries [4] however the effects of stent design parameters such as strut thickness and crown radius of curvature or analysis in realistic geometries is generally lacking. A more thorough understanding of the effect of a stent’s geometric parameters on the arterial flow will provide insight into their long-term performance and will lead to better design.

Download Full-text

Effects of Stent Design Parameters on Normal Artery Wall Mechanics

Journal of Biomechanical Engineering ◽

10.1115/1.2246236 ◽

2006 ◽

Vol 128 (5) ◽

pp. 757-765 ◽

Cited By ~ 91

Author(s):

Julian Bedoya ◽

Clark A. Meyer ◽

Lucas H. Timmins ◽

Michael R. Moreno ◽

James E. Moore

Keyword(s):

Radial Displacement ◽

Design Parameters ◽

Radius Of Curvature ◽

Stent Design ◽

Artery Wall ◽

Element Analysis ◽

Radial Strength ◽

Stent Strut ◽

Invasive Techniques ◽

Normal Artery

A stent is a device designed to restore flow through constricted arteries. These tubular scaffold devices are delivered to the afflicted region and deployed using minimally invasive techniques. Stents must have sufficient radial strength to prop the diseased artery open. The presence of a stent can subject the artery to abnormally high stresses that can trigger adverse biologic responses culminating in restenosis. The primary aim of this investigation was to investigate the effects of varying stent “design parameters” on the stress field induced in the normal artery wall and the radial displacement achieved by the stent. The generic stent models were designed to represent a sample of the attributes incorporated in present commercially available stents. Each stent was deployed in a homogeneous, nonlinear hyperelastic artery model and evaluated using commercially available finite element analysis software. Of the designs investigated herein, those employing large axial strut spacing, blunted corners, and higher amplitudes in the ring segments induced high circumferential stresses over smaller areas of the artery’s inner surface than all other configurations. Axial strut spacing was the dominant parameter in this study, i.e., all designs employing a small stent strut spacing induced higher stresses over larger areas than designs employing the large strut spacing. Increasing either radius of curvature or strut amplitude generally resulted in smaller areas exposed to high stresses. At larger strut spacing, sensitivity to radius of curvature was increased in comparison to the small strut spacing. With the larger strut spacing designs, the effects of varying amplitude could be offset by varying the radius of curvature and vice versa. The range of minimum radial displacements from the unstented diastolic radius observed among all designs was less than 90μm. Evidence presented herein suggests that stent designs incorporating large axial strut spacing, blunted corners at bends, and higher amplitudes exposed smaller regions of the artery to high stresses, while maintaining a radial displacement that should be sufficient to restore adequate flow.

Download Full-text

Effects of Metal Material Stent Design Parameters on Longitudinal Stent Strength

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.723.299 ◽

2016 ◽

Vol 723 ◽

pp. 299-304 ◽

Cited By ~ 1

Author(s):

Xiang Shen ◽

Zhong Min Xie ◽

Yong Quan Deng ◽

Song Ji

Keyword(s):

Finite Element Method ◽

Finite Element ◽

Blood Vessel ◽

Design Parameters ◽

Curvature Radius ◽

Stent Design ◽

Rigid Surface ◽

Stent Deployment ◽

Metal Material ◽

Stent Deformation

The longitudinal stent deformation (LSD) was usually caused by the external force in the blood vessel. The effects of metal material stent design parameters on the longitudinal stent strength (LSS) were studied using finite element method (FEA). A longitudinal stent compression model was developed and a rigid surface was used to compress the stent after stent deployment in coronary arteries. Results showed that the connector length, the strut amplitude and the curvature radius at the crown junctions influenced the LSS hardly. However, the number of connector played the most significant role in the LSS, and increasing the number of connectors can substantially improve the LSS, and the LSS of stent with four connectors was nearly three times than that of the stent with two connectors. For the shape of connector, the LSS of the S-stent, M-stent and L-stent were successively increased. With regard to the L-stent, increasing the width of connector can improve the LSS. Reasonably changing stent design parameters can effectively strengthen the LSS. Conclusions obtained from this paper can help surgeons to select appropriate stents and designers to optimize the stent design to reduce the LSD.

Download Full-text

Expansion Performance of Novel Balloon-Expandable Stent for Tapered Vessel

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.645-646.1333 ◽

2015 ◽

Vol 645-646 ◽

pp. 1333-1338

Author(s):

Xiang Shen ◽

Yang Yang Sun ◽

Bo Bo Wu

Keyword(s):

Finite Element Method ◽

Radial Displacement ◽

Design Parameters ◽

The Novel ◽

Stent Design ◽

Positioning Accuracy ◽

Stent Restenosis ◽

Expansion Pressure ◽

Stent Expansion ◽

In Stent Restenosis

In-stent restenosis still remains an obsession to cardiologist, especially in tapered vessels. In this paper, we designed a novel balloon-expandable stent for tapered vessel and proposed a finite element method (FEM) to study the expansion of the novel stent. The effect of stent design parameters on stent tapering and foreshortening were also researched. Results show that the radial displacement of stent proximal end was always larger than that of stent distal end during stent expansion, and the stent had a tapered shape as a whole after expansion. The degree of stent tapering observed increased with the expansion pressure increase. Besides, increasing the gradient of ring amplitude not only could increase the tapering degree of stent after expansion, but also could decrease stent foreshortening, improving the positioning accuracy after stent implantation. In conclusion, FEM can quantify expansion performance of novel balloon-expandable stents and help designers to devise and assess new stent designs for tapered vessel.

Download Full-text

Optimization of stent designs regarding the thrombosis risk using computational fluid dynamics

Current Directions in Biomedical Engineering ◽

10.1515/cdbme-2018-0024 ◽

2018 ◽

Vol 4 (1) ◽

pp. 93-96

Author(s):

Carolin Wüstenhagen ◽

Sylvia Pfensig ◽

Stefan Siewert ◽

Sebastian Kaule ◽

Niels Grabow ◽

...

Keyword(s):

Fluid Dynamics ◽

Computational Fluid Dynamics ◽

Shear Stress ◽

Wall Shear Stress ◽

Stent Thrombosis ◽

Fluid Simulation ◽

Design Parameters ◽

Stent Design ◽

Thrombosis Risk ◽

Wall Shear

AbstractIn-stent thrombosis is a major complication of stent implantations. Unlike pathological occurrences as in-stent restenosis for instance, thrombosis represents an acute event associated with high mortality rates. Experiments show that low wall shear stress promotes undirected endothelial cell coverage of the vessel wall and therefore increases the risk of thrombus formation. Stent design represents a crucial factor influencing the surface areas of low wall shear stress and thus the incidence of acute in-stent thrombosis. In this study, we present an optimization method for stent designs with minimized thrombosis risk. A generic stent design was developed, based on five different stent design parameters. Optimization was conducted based on computational fluid dynamics analysis and the gradient-free Nelder-Mead approach. For each optimization step, a numerical fluid simulation was performed in a vessel with a reference vessel diameter of 2.70 mm with stent-overexpansion ratio of 1.0:1.1. For each numerical fluid simulation a physiological Reynolds number of 250, resulting in a mean velocity of 0.331 m/s at the inlet and a laminar flow as well as stiff vessel walls were assumed. The impact of different stent designs was analyzed based on the wall shear stress distribution. As a basis for the comparison of different stent designs, a dimensionless thrombosis risk number was calculated from the area of low wall shear stress and the overall stented area. The first two optimization steps already provide a decrease of thrombosis risk of approximately 83%. In conclusion, computational fluid dynamic analyses and optimization methods usind the Nelder-Mead approach represent a useful tool for the development of hemodynamically optimized stent designs with minimized thrombosis risk.

Download Full-text

Design and Optimization of Functionally Graded Superelastic NiTi Stents

Volume 11A: 46th Design Automation Conference (DAC) ◽

10.1115/detc2020-22706 ◽

2020 ◽

Author(s):

Jivtesh B. Khurana ◽

Mary Frecker ◽

Eric M. Pauli

Keyword(s):

Mechanical Model ◽

Bending Moment ◽

Material Design ◽

Functionally Graded ◽

Design Parameters ◽

Stent Design ◽

Niti Wire ◽

Element Analysis ◽

Off Label ◽

Initial Location

Abstract Endoscopic stents are being used by surgeons in off-label uses to manage leaks and perforations in the gastrointestinal tract. Commercially available stents are primarily designed to open strictures in the esophagus through tissue compression. The stents incorporate a woven NiTi wire to produce a stiff and linear tubular shape that conforms to the esophagus. In off-label uses, where the stents are placed in non-esophageal locations the stents must bend, the stents show a high propensity to migrate from their initial location causing unwanted complications. In this paper, a new stent design incorporating functionally graded NiTi is presented and explored. First, a functionally graded NiTi stent design is proposed. Next, a mechanical model using finite element analysis is developed to predict the bending moment and stiffness of the functionally graded stent designs. Finally, the mechanical model is coupled with a genetic algorithm in MATLAB to identify optimal designs. For a 90° bending angle, the best design parameters of the newly proposed flexible stents are found for three different stent design families. The results of the functionally graded stents show how tailoring the material properties locally in a structure can lead to highly compliant behavior. The tailoring of the geometric and material design developed may be applied to design of highly flexible and optimized medical devices.

Download Full-text

Effect of Stent Design Parameters on Hemodynamics and Blood Damage in a Percutaneous Cavopulmonary Assist Device

Volume 2: Development and Applications in Computational Fluid Dynamics; Industrial and Environmental Applications of Fluid Mechanics; Fluid Measurement and Instrumentation; Cavitation and Phase Change ◽

10.1115/fedsm2018-83210 ◽

2018 ◽

Author(s):

Jakin Jagani ◽

Elizabeth Mack ◽

Jihyeon Gong ◽

Alexandrina Untaroiu

Keyword(s):

Vena Cava ◽

Pressure Rise ◽

Design Parameters ◽

Stent Design ◽

Damage Potential ◽

Assist Device ◽

Strut Thickness ◽

Blood Damage ◽

Stent Length ◽

Hemodynamic Performance

Hypoplastic Right Heart Syndrome is a type of congenital heart defect where the right ventricle is underdeveloped in an infant to pump blood from the body to the lungs. The three-staged surgical Fontan procedure provides a temporary treatment; however, in most of the cases, a heart transplantation is required due to postoperative complications. Currently, there are no devices commercially available in the market to provide a therapeutic assistance to these patients until a donor heart is available. Thus, a novel dual propeller pump concept is developed to provide cavopulmonary assistance to these patients. The designed blood pump would be percutaneously inserted via the Femoral vein and deployed at the center of the Total Cavopulmonary Connection (TCPC). The two propellers, each placed in the Superior Vena Cava (SVC) and the Inferior Vena Cava (IVC) are connected by a single shaft and rotating at same speed. The device is supported with the help of a self-expanding stent whose outer walls are anchored to the inner walls of the IVC and the SVC. Each of the IVC and the SVC propeller without the stent provides a modest pressure augmentation of 5–6 mm Hg. To expand on this, the current study focusses on studying the effect of the introduction of stent around the propeller on the hemodynamic performance of the pump. Five different stent design parameters, viz. the strut thickness, width, number, the stent length and number of strut columns were selected for a range of values. Each of the design parameters was varied by keeping all others constant and equal to the base stent design. All the stent models were analysed to see their effect on pressure rise, flow pattern and blood damage using 3D CFD analysis. The blood damage potential for different studied designs was predicted using a non-linear mathematical power law model along with Lagrangian particle tracking to predict the blood flow path. The introduction of stent resulted in pressure reduction of around 0.4 and 0.2 mm Hg around the IVC and SVC propeller with an increase in blood damage index (BDI) by almost 2 times for the final dual propeller pump assembly. It was observed that the blood damage potential was directly related to the amount of pressure rise where the stent length, stent column number, strut width, and strut thickness had a converse effect showing a reduction in pressure rise and blood damage with their increment. While the number of struts gave a desirable effect of increasing pressure rise and reducing blood damage with its increment. The study also demonstrated that the introduction of stent around a circulatory pump increases the Wall Shear Stress (WSS) value at the stent-artery wall interface thereby preventing the occurrence of restenosis and thrombosis initiating due to very low WSS (< 0.5 Pa). Thus, this study acts as an initial step to design a protective stent support around a percutaneous assist device by analysing the sensitivity of stent design parameters on the hemodynamic performance of the pump.

Download Full-text