A novel microscopic assay of transient platelet-von Willebrand factor adhesion, kinetics, margination, and blood rheology.

摘要

Platelets play a central role in hemostasis and arterial thrombosis. At high shear rates, von Willebrand factor (vWF) may recruit passive platelets to a growing thrombus via transient glycoprotein (GP) Ib binding, increasing platelet residence time to allow activation by stress or chemical agonists. Platelet accumulation also depends on dispersive transport driven by shear flow of red blood cells (BBC's), platelet margination (a near-wall enrichment of platelet concentration due to persistent lateral drift), and flow-induced stresses.;A new assay was developed that enables simultaneous measurement of platelet adhesion, platelet margination, wall shear stress, and non-Newtonian flow velocity profile, in blood flow through protein-coated capillaries. Transient platelet adhesion, translation, and embolization are measured by video microscopy. Translating-stage image sequences measure platelet concentration at 3 +/- 1 micron from the capillary surface and centerline flow velocity. The blood velocity profiles are fit to a Casson model based on flow rate, centerline velocity, and pressure gradient.;In capillaries coated with plasma vWF, platelet adhesion was an increasing function of wall shear rate between 126 and 840/s. Margination increased with shear rate, and decreased on vWF-coated capillaries compared to albumin controls. The characteristic time constant for transient binding on plasma vWF was 1.0 to 1.4 sec. A platelet flux balance was performed on a control volume within 2 mum of the vessel wall using near-wall concentration data, estimated convective flux, and surface net accumulation rate. Dispersive flux was an order of magnitude faster than the convective flux, meaning stronger contribution of shear-induced dispersion to the contact of platelet with thrombogenic surface, tethering or adhesion, accumulation, and aggregation of platelets than the convective motion. The new assay provides a wealth of data for cell-level computational modeling of platelet adhesion mechanics and kinetics under controlled flow.