Background: Occlusive thrombi can rapidly form under high shear rates to cause a heart attack or stroke. The growth (Casa and Ku (2017)) and contraction (Muthard and Diamond (2012)) of thrombi have been investigated in previous studies and can occur when an atherosclerotic plaque ruptures within a few minutes making it an acute life-threatening process.

Aims: We study the influence of shear rate and the presence of red blood cells on the platelet adhesion, aggregation and clot retraction.

Methods: Two microfluidic flow systems with a stenosis were perfused with porcine whole blood (WB) or platelet-rich plasma (PRP) at high shear rates (3,000 – 13,000 s^-1). The systems were driven by a constant pressure and coated with type I collagen. Outflow mass data and microscopic images were used to determine the lag times, occlusion times, rapid platelet accumulation (RPA) rates, and retraction rates.

Results: WB occlusion times were similar to previously reported values. PRP showed a significantly longer lag time and lower RPA rate compared to WB in both devices that resulted in a long occlusion time (p< 0.01). In PRP, retraction of the clot was clearly visible upon flow arrest, being more pronounced downstream with a retraction rate of 7.2·10^-4 s^-1 (see Fig. 1).

Conclusions: The longer lag time and lower RPA rate in PRP may indicate that margination plays an important role in the lag and RPA phase of thrombus formation. The retraction rate was equal for all PRP experiments which suggests retraction is independent of the flow environment in which the clot has been formed.

[A thrombus at the time of occlusion (red) and at the end of the experiment (green). It retracted mostly downstream, where the red color is present. ]

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/in-vitro-occlusive-clot-growth-and-retraction/