Dynamics of Blood Flow and Thrombus Formation in a Multi-Bypass Microfluidic Ladder Network

Abstract

The reaction dynamics of a complex mixture of cells and proteins, such as blood, in branched circulatory networks within the human microvasculature or extravascular therapeutic devices such as extracorporeal oxygenation machine (ECMO) remains ill-defined. In this report we utilize a multi-bypass microfluidics ladder network design with dimensions mimicking venules to study patterns of blood platelet aggregation and fibrin formation under complex shear. Complex blood fluid dynamics within multi-bypass networks under flow were modeled using COMSOL. Red blood cells and platelets were assumed to be non-interacting spherical particles transported by the bulk fluid flow, and convection of the activated coagulation factor II, thrombin, was assumed to be governed by mass transfer. This model served as the basis for predicting formation of local shear rate gradients, stagnation points and recirculation zones as dictated by the bypass geometry. Based on the insights from these models, we were able to predict the patterns of blood clot formation at specific locations in the device. Our experimental data was then used to adjust the model to account for the dynamical presence of thrombus formation in the biorheology of blood flow. The model predictions were then compared to results from experiments using recalcified whole human blood. Microfluidic devices were coated with the extracellular matrix protein, fibrillar collagen, and the initiator of the extrinsic pathway of coagulation, tissue factor. Blood was perfused through the devices at a flow rate of 2 µL/min, translating to physiologically relevant initial shear rates of 300 and 700 s−1 for main channels and bypasses, respectively. Using fluorescent and light microscopy, we observed distinct flow and thrombus formation patterns near channel intersections at bypass points, within recirculation zones and at stagnation points. Findings from this proof-of-principle ladder network model suggest a specific correlation between microvascular geometry and thrombus formation dynamics under shear. This model holds potential for use as an integrative approach to identify regions susceptible to intravascular thrombus formation within the microvasculature as well as extravascular devices such as ECMO.

Platelet “first responders” in wound response, cancer, and metastasis

“…The exposure PS-Ag-Cyto complexes on the outer leaflet of PMP creates surface for assembly of a Factor V and Factor Xa catalytic complexes that generate thrombin. Thrombin-mediated cleavage of fibrinogen leads to fibrin clot formation and entrapment of additional platelets at wound sites [165–168]. Fibrinolysis then ensues to control clot growth [165,166].…”

“…Thrombin-mediated cleavage of fibrinogen leads to fibrin clot formation and entrapment of additional platelets at wound sites [165–168]. Fibrinolysis then ensues to control clot growth [165,166]. PMPs also interact with immune cells via adhesion molecules such as selectins that selectively bind carbohydrate molecules associated with immune function [121,169,142,144].…”

Thrombi Produced in Stagnation Point Flows Have a Core–Shell Structure

“…This device may be suited for studying clotting in pulsatile inlet flow conditions where the stagnation point doesn’t move. Additionally, a more detailed calculation of the cell-free layer and hematocrit could be achieved using a particle suspension model 24 to further improve the computational fluid dynamics model.…”

Utility of microfluidic devices to study the platelet–endothelium interface

“…[84–86] In vivo , ECs at vascular branch points and bifurcations have been shown to endure disturbed blood flow profiles,[87] which have been implicated in vessel susceptibility to thrombosis and atherosclerotic plaque formation or rupture. [52,88,89] PDMS microfludic devices have been used to show that perturbations of flow due to engineered stenosis and vessel branch points directly affect EC expression parameters of vascular cell adhesion molecules, such as VCAM-1, NO and the integrity of gap junctions between ECs.…”