Computational fluid dynamics and stent design.
ABSTRACT Stents are small, usually metallic tubes that are intended to prop open arteries blocked with atherosclerotic plaques. While stents have been used successfully in recent years, they still suffer from failure due to development of new tissue in stented segment (restenosis). Variations in the failure rates associated with different stent designs have led researchers to investigate the role of near-wall flow patterns. While there is no direct evidence yet, the patterns of flow stagnation as the blood flows past the stent struts may affect the restenosis process. Computational fluid dynamics (CFD) approaches are well suited for obtaining detailed information on stent flow patterns. Many CFD simulations make use of a two-dimensional model. The strong dependence of flow stagnation on stent strut spacing has been clearly demonstrated. These results have been employed to interpret the results of in vitro experiments designed to elucidate the mechanisms of restenosis.
[show abstract] [hide abstract]
ABSTRACT: Stents are artificial implants that provide scaffolding to a cavity inside the body. This paper presents a new luminal device for reducing the mechanical failure of stents due to recoil, which is one of the most important issues in stenting. This device, which we call a recoil-resilient ring (RRR), is utilized standalone or potentially integrated with existing stents to address the problem of recoil. The proposed structure aims to minimize the need for high-pressure overexpansion that can induce intra-luminal trauma and excess growth of vascular tissue causing later restenosis. The RRR is an overlapped open ring with asymmetrical sawtooth structures that are intermeshed. These teeth can slide on top of each other, while the ring is radially expanded, but interlock step-by-step so as to keep the final expanded state against compressional forces that normally cause recoil. The RRRs thus deliver balloon expandability and, when integrated with a stent, bring both radial rigidity and longitudinal flexibility to the stent. The design of the RRR is investigated through finite element analysis (FEA), and then the devices are fabricated using micro-electro-discharge machining of 200-μm-thick Nitinol sheet. The standalone RRR is balloon expandable in vitro by 5–7 Atm in pressure, which is well within the recommended in vivo pressure ranges for stenting procedures. FEA compression tests indicate 13 × less reduction of the cross-sectional area of the RRR compared with a typical stainless steel stent. These results also show perfect elastic recovery of the RRR after removal of the pressure compared to the remaining plastic deformations of the stainless steel stent. On the other hand, experimental loading tests show that the fabricated RRRs have 2.8 × radial stiffness compared to a two-column section of a commercial stent while exhibiting comparable elastic recovery. Furthermore, testing of in vitro expansion in a mock artery tube shows around 2.9% recoil, approximately 5–11 × smaller than the recoil reported for commercial stents. These experimental results demonstrate the effectiveness of the device design for the targeted luminal support and stenting applications. (Some figures may appear in colour only in the online journal)Journal of Micromechanics and Microengineering 01/2013; 23:65001. · 2.11 Impact Factor
Article: Predicting neointimal hyperplasia in stented arteries using time-dependant computational fluid dynamics: a review.[show abstract] [hide abstract]
ABSTRACT: This paper reviews the recent literature regarding the time-dependent computational fluid dynamics (CFD) analyses of blood flow through implanted coronary stents. The in vivo processes which result in arterial restenosis are identified. The definition and range of the computationally predicted variables which are believed to stimulate the restenosis processes are evaluated. The reviewed literature is subdivided into effect-based in which the effects of altering the flow model are investigated and design-based in which different geometric stent configurations are compared. Finally, conclusions are made regarding the body of work reviewed and recommendations are provided for future work in this field.Computers in biology and medicine 03/2010; 40(4):408-18. · 1.27 Impact Factor
[show abstract] [hide abstract]
ABSTRACT: The treatment of atherosclerotic plaques near and involving coronary bifurcations is especially challenging for interventional procedures. Optimization of these treatment strategies should begin with an understanding of how disease came to be localized to these regions, followed by careful design of the interventional tools and implanted devices. This manuscript reviews the basic biomechanics of coronary bifurcations, stented arteries, and the complex biomechanical challenges associated with bifurcation stenting. Flow patterns in bifurcations are inherently complex, including vortex formation and creation of zones of low and oscillating wall shear stress that coincide with early intimal thickening. Bifurcation geometry (in particular, the angle between the side branches), is of paramount importance in creating these proatherogenic conditions. This predilection for disease formation leads to a large number of bifurcation lesions presenting for clinical intervention. Therefore, several strategies have developed for treating these challenging lesions, including both dedicated devices and creative adaptation of single vessel lesion technologies. The biomechanical implications of these strategies are likely important in short and long term clinical outcomes. While the biomechanical environment in a stented coronary bifurcation is extremely challenging to model, computational methods have been deployed recently to better understand these implications. Enhancement of clinical success will be best achieved through the collaborative efforts of clinicians, biomechanicians, and device manufacturers.Catheterization and Cardiovascular Interventions 11/2010; 76(6):836-43. · 2.29 Impact Factor