The use of microfluidics in hemostasis: clinical diagnostics and biomimetic models of vascular injury

Abstract

Purpose of review: This article reviews the application of microfluidic technologies in hemostasis. The emphasis is on promising developments in devices for clinical applications and novel approaches to modeling complex hemodynamics.

Recent findings: Microfluidics combined with micropatterning of prothrombotic substrates provides devices for measuring platelet function and coagulation with low blood volumes (∼100 μl) over a wide range of shear stresses. This technology has been applied to the diagnosis of bleeding and thrombotic disorders, as well as to dosing and monitoring of anticoagulation and antiplatelet agents. Microfluidic devices that mimic vascular geometries such as bifurcations, stenosis, and complex interconnected networks yield complex flow fields that have revealed new mechanisms of platelet adhesion and aggregation. Applying techniques from tissue engineering by endothelializing these networks is beginning to close the gap between in-vitro and in-vivo models of vascular injury.

Summary: Microfluidic technology enables researchers to create in-vitro models of vascular disease with unprecedented control of the biochemical and biophysical conditions. Two promising directions are flow-dependent clinical assays and biomimetic vascular networks. These approaches are particularly well suited for modeling the microvasculature. However, caution should be used when extrapolating results from microfluidic channels to the pathophysiology of thrombosis in large arteries and veins.

FIGURE 1.

Microfluidic devices for measuring hemostasis and thrombosis under physiological and pathological flow conditions. (a) High-throughput device for measuring platelet function over a range of shear rates on ~300 micropatterned collagen spots [6^■]. Channels are 250 μm wide and 50 μm high. (b) Side-channel design for measuring intersitial flows through thrombi at controlled pressure gradients [26^■]. The side channel is filled with collagen and TF. Blood flow runs perpendicular to the side channel at a known flow rate (Q1). The thrombus consists of a fibrin-rich zone within and adjacent to the collagen–TF and platelet-rich outer shell. (c) Endothelialized microvascular mimic for measuring thrombotic occlusions [44]. Endothelial cells were treated with the toxin STX to simulate HUS resulting in VWF secretion and subsequent accumulation of platelet and leukocytes. Channels are ~30 μm in diameter. (d) Platelets preferentially aggregate downstream of the stenotic region in this microfluidic model of atherosclerotic geometry [49^■]. Platelet accumulation increases with increasing occlusion as seen in the difference between an 80% occlusion and 60% occlusion of a 300 μm-wide channel. VWF/fibrinogen strips are used to differentiate the spatial dependence of platelet accumulation in different areas of the stenosis. (e) Endothelialized microfluidic vessel networks embedded in a collagen gel [46^■■]. Endothelial cells are stained for CD31 and nuclei. Note that the cross-section of these channels is semicircular, which avoids low-flow regions inherent in rectangular channels. TF, tissue factor; HUS, hemolytic–uremic syndrome; STX, shiga toxin type 2; VWF, von Willebrand factor.