Effect of blood flow patterns on localized platelet adhesion under physiologic flow conditions using two-dimensional and three-dimensional stent models - an experimental and computational approach

Abstract

This dissertation presents dynamic flow experiments with fluorescently labeled platelets to allow for spatial observation of wall attachrent 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 (1) a parallel plate flow chamber that contained two-dimensional (2D) stents that feature completely recirculating flow, partially recirculating flow, and completely reattached flow, and (2) a three-dimensional (3D) cylindrical tube that contained stents of various geometric designs. Flow detachment and reattachment points exhibited very low platelet deposition. Platelet deposition was very low in the recirculation regions in the 3D stents unlike the 2D stents. Deposition distal to a strut was always high in 2D and 3D stents. Spirally recirculating regions were found in 3D unlike in 2D stents, where the deposition was higher than at well-separated regions of recirculation. Platelet deposition occurred through convective transport of platelets as defined by the instantaneous streamlines. The instantaneous streamlines were obtained from computational fluid dynamics models of the different stents used with the same experimental flow conditions. Platelet deposition was higher in areas where the blood flow was directed towards the wall and lower in areas where the blood flow was directed away from the wall. Though the platelet deposition patterns shown in this paper were a result of a short time-scale phenomena, convective transport plays an essential role in the interaction of blood cells with the endothelial or exposed underlying collagen layer, which In turn affects the development of Intimal hyperplasia (IH). These results could help in improved stent designs In future that prevent excessive platelet aggregation.