Mass transfer limitations of blood clot formation on tissue factor and its role in the pathophysiology of hemophilia A and C

Abstract

One of the grand challenges in medicine is controlling the balance between bleeding, normal blood clot formation and excessive clotting, or thrombosis. The focus of this thesis is on the development of microfluidic devices to measure the biochemical network known as coagulation under physiological flow conditions and the mass transfer limitations that regulate bleeding in hemophilia. Under reaction-limited conditions, blood flow provides a continual source of reactants for these reactions. Under transport-limited conditions, blood flow dilutes coagulation products so that they do not accumulate near the injury site. Reaction-limited and transport-limited regimes were identified in experiments with factors VIII, IX and XI deficient plasmas and whole blood as a function of shear rate and tissue factor (TF) concentration. In plasma, coagulation was reaction-limited at wall shear rates of less 250 s[superscript -1] on high concentrations of surface bound TF. Coagulation was transport-limited at shear rate of greater than or equal 250 s[superscript -1], at low TF, or in the absence of FVIII or FIX. FXI played a role in fibrin deposition, morphology and lysis at both low and high TF concentration, whereas it only plays a role in low TF under static conditions. In whole blood, we found FVIII deficiencies profoundly influence thrombin and fibrin formation on TF-rich substrates. In the case of mild FVIII deficiencies (5-30% normal levels) the local thrombin concentration is sufficient to promote fibrin formation in and adjacent to platelet aggregates. Fibrin formation was not supported by severe (<1%) or moderate (1-5%) deficiencies. Treatment with recombinant FVIII normalized fibrin deposition. Whereas, treatment with recombinant FVIIa creates a reaction-limited condition where clots form faster and are larger than healthy controls, suggesting that this drug could convert a bleeding disorder to a thrombotic event at therapeutic doses.