Investigation of platelet margination phenomena at elevated shear stress.
ABSTRACT Thrombosis is a common complication following the surgical implantation of blood contacting artificial organs. Platelet transport, which is an important process of thrombosis and strongly modulated by flow dynamics, has not been investigated under the shear stress level associated with these devices, which may range from tens to several hundred Pascal.The current research investigated platelet transport within blood under supra-physiological shear stress conditions through a micro flow visualization approach. Images of platelet-sized fluorescent particles in the blood flow were recorded within microchannels (2 cm x 100 microm x 100 microm). The results successfully demonstrated the occurrence of platelet-sized particle margination under shear stresses up to 193 Pa, revealing a platelet near-wall excess up to 8.7 near the wall (within 15 microm) at the highest shear stress. The concentration of red blood cells was found to influence the stream-wise development of platelet margination which was clearly observed in the 20% Ht sample but not the 40% Ht sample. Shear stress had a less dramatic effect on the margination phenomenon than did hematocrit. The results imply that cell-cell collision is an important factor for platelet transport under supra-physiologic shear stress conditions. It is anticipated that these results will contribute to the future design and optimization of artificial organs.
SourceAvailable from: Gábor Závodszky[Show abstract] [Hide abstract]
ABSTRACT: Thrombus formation is a thoroughly researched area, posing several unanswered questions. Quite many of the underlying processes are still not well understood. This uncertainty arises from the fact that the blood clotting mechanism in our bodies involves a rather complex reaction cascade with plenty of components. These underlying dynamic processes stretch over the domains of several disciplines (as there are biomechanical and biochemical reactions as well as fluid dynamical components). In this study the factors thought to be the most influential were selected and coupled with the transient flow field that reacts not only to the cardiac pressure waves but also to the changing geometry of the vessel due to the clot formation. Although the number of degrees of freedom is reduced heavily, this model is already capable of qualitatively reproducing the results of in-vivo measured hemostasis.
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ABSTRACT: Despite the importance of platelets in the formation of a thrombus, their transport in complex flows has not yet been studied in detail. In this paper we simulated red blood cells and platelets to explore their transport behaviour in aneurysmal geometries. We considered two aneurysms with different aspect ratios (AR = 1.0, 2.0) in the presence of fast and slow blood flows (Re = 10, 100), and examined the distributions of the cells. Low velocities in the parent vessel resulted in a large stagnation zone inside the cavity, leaving the initial distribution almost unchanged. In fast flows, an influx of platelets into the aneurysm was observed, leading to an elevated concentration. The connection of the platelet-rich cell-free layer (CFL) with the outer regions of the recirculation zones leads to their increased platelet concentration. These platelet-enhanced recirculation zones produced a diverse distribution of cells inside the aneurysm, for the different aspect ratios. A thin red blood CFL that was occupied by platelets was observed on the top of the wide-necked aneurysm, whereas a high-haematocrit region very close to the vessel wall was present in the narrow-necked case. The simulations revealed that non-trivial distributions of red blood cells and platelets are possible inside aneurysmal geometries, giving rise to several hypotheses on the formation of a thrombus, as well as to the wall weakening and the possible rupture of an aneurysm.Interface focus: a theme supplement of Journal of the Royal Society interface 04/2013; 3(2):20120089. DOI:10.1098/rsfs.2012.0089 · 3.12 Impact Factor
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ABSTRACT: Although the thrombogenic nature of the surfaces of cardiovascular devices is an important aspect of blood biocompatibility, few studies have examined platelet deposition onto opaque materials used for these devices in real time. This is particularly true for the metallic surfaces used in current ventricular assist devices (VADs). Using hemoglobin depleted red blood cells (RBC ghosts) and long working distance optics to visualize platelet deposition, we sought to perform such an evaluation. Fluorescently labeled platelets mixed with human RBC ghosts were perfused across 6 opaque materials (a titanium alloy (Ti6Al4V), silicon carbide (SiC), alumina (Al2O3), 2-methacryloyloxyethyl phosphorylcholine polymer coated Ti6Al4V (MPC-Ti6Al4V), yttria partially stabilized zirconia (YZTP), and zirconia toughened alumina (ZTA)) for 5 min at wall shear rates of 400 and 1000 sec-1. Ti6Al4V had significantly increased platelet deposition relative to MPC-Ti6Al4V, Al2O3, YZTP, and ZTA at both wall shear rates (P <0.01). For all test surfaces, increasing the wall shear rate produced a trend of decreased platelet adhesion. The described system can be a utilized as a tool for comparative analysis of candidate blood-contacting materials with acute blood contact.Journal of Biomedical Materials Research Part A 04/2015; 103(4). DOI:10.1002/jbm.a.35202 · 2.83 Impact Factor