Threshold Response of Initiation of Blood Coagulation by Tissue Factor in Patterned Microfluidic Capillaries Is Controlled by Shear Rate

Abstract

Objective-Blood flow is considered one of the important parameters that contribute to venous thrombosis. We quantitatively test the relationship between initiation of coagulation and shear rate and suggest a biophysical mechanism to understand this relationship. Methods and Results-Flowing human blood and plasma were exposed to cylindrical surfaces patterned with patches of tissue factor (TF) by using microfluidics. Initiation of coagulation of normal pooled plasma depended on shear rate, not volumetric flow rate or flow velocity, and coagulation initiated only at shear rates below a critical value. Initiation of coagulation of platelet-rich plasma and whole blood showed similar behavior. At constant shear rate, coagulation of plasma also showed a threshold response to the size of a patch of TF, consistent with our previous work in the absence of flow. Conclusion-Initiation of coagulation of flowing blood displays a threshold response to shear rate and to the size of a surface patch of TF. Combined with the results of others, these results set the range of shear rates that limit initiation of coagulation by small surface areas of TF and by shear activation of platelets. This range fits the relatively narrow range of physiological shear rates described by Murray's law. T his article analyzes initiation of coagulation of blood flowing over a patch presenting tissue factor (TF) in the regime where platelets are not activated by shear alone. TF is the primary stimulus for initiation of coagulation in vivo. [1][2][3] We demonstrate that initiation of coagulation displays a threshold response to shear rate and to the size of the patch of TF, and we suggest a biophysical mechanism that explains these threshold phenomena. While low blood flow and endothelial damage are known risk factors for coagulation, 4 the precise effects of blood flow on the initiation of coagulation are not fully characterized, possibly because of the difficulty in experimentally decoupling the effects of volumetric flow rate, flow velocity, and shear rate.The effects of flow and shear rate on the activation of coagulation factors have been studied previously, 5-12 but whether high or low shear rates promote initiation of coagulation remains unclear. Intuitively, high blood flow and shear rates may promote coagulation by increasing the rate of delivery of coagulation proenzymes to sites of vascular damage. Indeed, high shear rates have been shown to increase the generation of factor Xa from surfaces coated with the TF and factor VIIa complex (TF-VIIa). 11 Moreover, high shear rates increase the potential for shear activation of platelets. 13,14 On the other hand, numeric simulations have predicted that low blood flow could promote initiation by reducing the removal of activated coagulation factors from surfaces of TF-VIIa, 15 and, clinically, stasis and low blood flow are considered risk factors for deep vein thrombosis (DVT). 16 Low shear rates have also been found to increase fibrin deposition and appearance of fibrin monomers, indicating that l...

Platelet Control of Fibrin Distribution and Microelasticity in Thrombus Formation Under Flow

“…removal of thrombin and fibrin monomers. 37 In accordance with our results, it has been shown that the thrombi formed in mesenteric venules after laser injury are surrounded by a fibrin cap. …”

“…30 Single-pass flow perfusion likely makes the difference here because under flow, the deposited platelets provide a rate-limiting surface for the formation of thrombin and subsequent fibrin, whereas the same flow removes procoagulant factors and hence restricts fibrin formation. 37 Remarkably, in reconstitution experiments, the addition of both platelets and red blood cells was required for complete reversal of dilution effects. By implication, this indicates that under conditions of flow and sufficient margination of platelets by red blood cells, a coagulant activity of >60% is required for unrestricted generation of fibrin.…”

Causal relationship between hyperfibrinogenemia, thrombosis, and resistance to thrombolysis in mice

“…Staining was slightly more intense in thrombi from saphenous vein than carotid artery, consistent with higher fibrin production in lower shear conditions. 27 Both carotid artery and saphenous vein thrombi from mice infused with human fibrinogen demonstrated more intense fibrin staining at the periphery of proteinaceous regions and intense, diffuse staining in regions containing erythrocytes (Figure 2). These findings suggest that hyperfibrinogenemia increased thrombus fibrin content in both high and low shear vessels.…”

“…Thrombi from saphenous veins appeared more fibrin-rich than thrombi from carotid arteries (Figure 2), consistent with observations that lower shear promotes fibrin deposition. 27 Notably, however, hyperfibrinogenemic mice demonstrated shortened TTOs and increased fibrin content in thrombi in both high and lower shear vessels (Figures 1, 2). These findings do not diminish a role for stasis in thrombosis but rather suggest that the contributions of shear are eclipsed in the setting of hyperfibrinogenemia and potentially other pathologies as well.…”

Macro- and microscale variables regulate stent haemodynamics, fibrin deposition and thrombomodulin expression

“…Low shear rate recirculation zones in the peristrut regions can entrap activated platelets where longer residence times retain coagulation factors to increase the probability of coagulation [10,37]. Thus, high shear rates on the surface of the strut and low shear rates in the peristrut recirculation zones are synergistic for thrombus formation.…”