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 90 microm. 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.

The deployment of a vascular stent aims to increase lumen diameter for the restoration of blood flow, but the accompanied alterations in the mechanical environment possibly affect the long-term patency of these devices. The primary aim of this investigation was to develop an algorithm to optimize stent design, allowing for consideration of competing solid mechanical concerns (wall stress, lumen gain, and cyclic deflection). Finite element modeling (FEM) was used to estimate artery wall stress and systolic/diastolic geometries, from which single parameter outputs were derived expressing stress, lumen gain, and cyclic artery wall deflection. An optimization scheme was developed using Lagrangian interpolation elements that sought to minimize the sum of these outputs, with weighting coefficients. Varying the weighting coefficients results in stent designs that prioritize one output over another. The accuracy of the algorithm was confirmed by evaluating the resulting outputs of the optimized geometries using FEM. The capacity of the optimization algorithm to identify optimal geometries and their resulting mechanical measures was retained over a wide range of weighting coefficients. The variety of stent designs identified provides general guidelines that have potential clinical use (i.e., lesion-specific stenting).

The biomechanical interaction of stents and the arteries into which they are deployed is a potentially important consideration for long-term success. Adverse arterial reactions to excessive stress and the resulting damage have been linked to the development of restenosis. Complex geometric features often encountered in these procedures can confound treatment. In some cases, it is desirable to deploy a stent across a region in which the diameter decreases significantly over the length of the stent. This study aimed to assess the final arterial diameter and circumferential stress in tapered arteries into which two different stents were deployed (one stiff and one less stiff). The artery wall was assumed to be made of a strain stiffening material subjected to large deformations, with a 10% decrease in diameter over the length of the stent. A commercially available finite element code was employed to solve the contact problem between the two elastic bodies. The stiffer stent dominated over arterial taper, resulting in a nearly constant final diameter along the length of the stent, and very high stresses, particularly at the distal end. The less stiff stent followed more closely the tapered contour of the artery, resulting in lower artery wall stresses. More compliant stents should be considered for tapered artery applications, perhaps even to the exclusion of tapered stents.

A coupled agent-based model (ABM) and finite element analysis (FEA) computational framework is developed to study the interplay of bio-chemo-mechanical factors in blood vessels and their role in maintaining homeostasis. The agent-based model implements the power of REPAST Simphony libraries and adapts its environment for biological simulations. Coupling a continuum-level model (FEA) to a cellular-level model (ABM) has enabled this computational framework to capture the response of blood vessels to increased or decreased levels of growth factors, proteases and other signaling molecules (on the micro scale) as well as altered blood pressure. Performance of the model is assessed by simulating porcine left anterior descending artery under normotensive conditions and transient increases in blood pressure and by analyzing sensitivity of the model to variations in the rule parameters of the ABM. These simulations proved that the model is stable under normotensive conditions and can recover from transient increases in blood pressure. Sensitivity studies revealed that the model is most sensitive to variations in the concentration of growth factors that affect cellular proliferation and regulate extracellular matrix composition (mainly collagen).

¤ ¤Purpose: To examine the solid mechanical effects of varying stent design and atherosclerotic plaque stiffness on the biomechanical environment induced in a diseased artery wall model. Methods: Computational modeling techniques were employed to investigate the final radius of the lumen and artery wall stresses after stent implantation. Two stent designs were studied (one stiff and one less stiff). The stenotic artery was modeled as an axisymmetrical diseased vessel with a 20% stenosis by diameter. The material properties of the diseased tissue in the artery models varied. Atherosclerotic plaques half as stiff (0.53), of equal stiffness (1.03), or twice as stiff (2.03) as the artery wall were investigated. Results: Final lumen radius was dependent on stent design, and the stiffer stent deformed the artery to an approximately 10% greater radius than the more compliant design. Alternatively, circumferential stress levels were dependent on both stent design and plaque material properties. Overall, the stiffer stent subjected the artery wall to much higher stress values than the more compliant design, with differences in peak values of 0.50, 0.31, and 0.09 MPa for the 2.03, 1.03, and 0.53 stiff plaques, respectively. Conclusion: Evidence suggests that a judicious choice of stent design can minimize stress while maintaining a patent lumen in stenotic arteries. If confronted with a rigid, calcified plaque, stent design is more important, as design differences can impose dramatically different stress fields, while still providing arterial patency. Alternatively, stent design is not as much of an issue when treating a soft, lipid-laden plaque, as stress fields do not vary significantly among stent designs. J Endovasc Ther 2008;15:643-654