The results indicate that stent design is crucial in determining the fluid mechanical environment in an artery. The sensitivity of flow characteristics to strut configuration could be partially responsible for the dependence of restenosis on stent design. From a fluid dynamics point of view, interstrut spacing should be larger in order to restore the disturbed flow; struts should be oriented to the flow direction in order to reduce the area of flow recirculation. Longitudinal connectors should be used only as necessary, and should be parallel to the axis. These results could guide future stent designs toward reducing restenosis.

Stent design and geometry influence the fluid mechanical environment in an artery and hence affect clinical outcomes of restenosis. There is clearly a role for biomechanics in improving current stent designs. This review summarizes some of the work that has been done to address the fluid mechanical aspects of stenting. A variety of computational, experimental, and in vivo approaches have been employed, and the results demonstrate a strong dependence on stent design, as well as effects on hemodynamics in locations of the circulatory system quite removed from the stented segment. There are also important solid mechanical aspects that affect clinical failures of stents that are not summarized here.

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Computer modeling and simulation is a powerful tool for assessing the performance of medical devices such as bioprosthetic heart valves (BHVs) that promises to accelerate device design and regulation. This study describes work to develop dynamic computer models of BHVs in the aortic test section of an experimental pulse-duplicator platform that is used in academia, industry, and regulatory agencies to assess BHV performance. These computational models are based on a hyperelastic finite element extension of the immersed boundary method for fluid–structure interaction (FSI). We focus on porcine tissue and bovine pericardial BHVs, which are commonly used in surgical valve replacement. We compare our numerical simulations to experimental data from two similar pulse duplicators, including a commercial ViVitro system and a custom platform related to the ViVitro pulse duplicator. Excellent agreement is demonstrated between the computational and experimental results for bulk flow rates, pressures, valve open areas, and the timing of valve opening and closure in conditions commonly used to assess BHV performance. In addition, reasonable agreement is demonstrated for quantitative measures of leaflet kinematics under these same conditions. This work represents a step towards the experimental validation of this FSI modeling platform for evaluating BHVs.

Computer modeling and simulation (CM&S) is a powerful tool for assessing the performance of medical devices such as bioprosthetic heart valves (BHVs) that promises to accelerate device design and regulation. This study describes work to develop dynamic computer models of BHVs in the aortic test section of an experimental pulse duplicator platform that is used in academia, industry, and regulatory agencies to assess BHV performance. These computational models are based on a hyperelastic finite element extension of the immersed boundary method for fluid--structure interaction (FSI). We focus on porcine tissue and bovine pericardial BHVs, which are commonly used in surgical valve replacement. We compare our numerical simulations to experimental data from two similar pulse duplicators, including a commercial ViVitro system and a custom platform related to the ViVitro pulse duplicator. Excellent agreement is demonstrated between the computational and experimental results for bulk flow rates, pressures, valve open areas, and the timing of valve opening and closure in conditions commonly used to assess BHV performance. In addition, reasonable agreement is demonstrated for quantitative measures of leaflet kinematics under these same conditions. This work represents a step towards the experimental validation of this FSI modeling platform for evaluating BHVs.

This paper presents dynamic flow experiments with fluorescently labeled platelets to allow for spatial observation of wall attachment in inter-strut spacings, to investigate their relationship to flow patterns. Human blood with fluorescently labeled platelets was circulated through an in vitro system that produced physiologic pulsatile flow in a parallel plate flow chamber that contained three different stent designs that feature completely recirculating flow, partially recirculating flow (intermediate strut spacing), and completely reattached flow. Highly resolved spatial distribution of platelets was obtained by imaging fluorescently labeled platelets between the struts. Platelet deposition was higher in areas where flow is directed towards the wall, and lower in areas where flow is directed away from the wall. Flow detachment and reattachment points exhibited very low platelet deposition. Platelet deposition within intermediate strut spacing continued to increase throughout the experimental period, indicating that the deposition rate had not plateaued unlike other strut spacings. The spatial uniformity and temporal increase in platelet deposition for the intermediate strut spacing confirms and helps explain our previous finding that platelet deposition was highest with this strut spacing. Further experimental investigations will include more complex three-dimensional geometries.

Background-Four commercially available stent designs (two balloon expandable -Bx Velocity and NIR and two self-expanding -Wallstent and Aurora) were modeled to compare the near wall flow characteristics of stented arteries using computational fluid dynamics (CFD) simulations under pulsatile flow conditions.

We performed a time course study in order to define the in vivo relationship between the induction of active suppression of contact sensitization and the presence of various cells in ultraviolet-exposed dermis and epidermis implicated in locally inducible immune tolerance: class II major histocompatibility complex (MHC)+CD11b(lo)Gr-1- Langerhans cells (LC), class II MHC-CD45+CD3+ dendritic epidermal T cells, class II MHC+CD11b+Gr-1- monocytes or class II MHC+CD11b+Gr-1+ monocytic/macrophagic cells. Partial tolerance (50%) was first detectable 6 h after a single 72 mJ/cm2 ultraviolet B exposure and maximum tolerance at 48 h post-ultraviolet exposure. By flow cytometry, a low granularity LC subset had disappeared from the epidermis within 6 h after ultraviolet exposure, followed by a slower decrease in the high granularity Langerhans cells subset. Within the dermis at the 6-h time point, small numbers of infiltrating monocytic/macrophagic cells are already apparent. By 24 h post-ultraviolet exposure, at which time tolerance has increased to 70%, the infiltrating monocytic/macrophagic population had risen to 1.2% of the total dermal cell population and was observed for the first time in the epidermis along with other infiltrating leukocytes (i.e., polymorphonuclear leukocytes). By 48 h post-ultraviolet exposure, when a state of maximum tolerance is obtained, both constitutive epidermal and dermal antigen-presenting cell populations were at or near their nadir of depletion. The infiltrating monocyte/macrophage population, however, exhibited a dramatic increase in the epidermis at 48 and 72 h. Thus, the ability to locally induce a state of in vivo tolerance is closely associated with the expansion of class II MHC+CD11b+Gr-1+ and -monocytic/macrophagic cells in the dermis and epidermis.