Computational Modeling and Microfluidics Reveal Characteristic Patterns of Regulation of Clot Structure and Mechanics By Tissue Factor Localization

The growth of a blood clot is initiated by tissue factor (TF) exposure and is expected to depend on TF localization (i.e., its level and spatial distribution). We sought to understand how the structural and mechanical properties of clots under flow are shaped by simultaneously varying the surface density of TF and its area of exposure. We used a microfluidic device harboring thrombogenic surfaces that differed in length and TF surface density. We perfused human whole blood through this device and continually measured platelet deposition, thrombin formation, and fibrin accumulation by means of fluorescence microscopy. Using our recently developed, detailed mathematical model of spatial clot growth under flow, we performed computational simulations to gain insights into the connection between the structure of a clot and its mechanical properties, such as resistance to blood flow and flow axial velocity.

We detected a non-additive, synergistic influence of the thrombogenic surface length and TF surface density on bulk thrombin and fibrin generation. We found that thrombogenic surface length and TF density controlled not only bulk accumulation, but also the occlusivity of the deposited platelet mass, as well as clot resistance to flow. The extent of this control depended on the blood flow velocity. An increase in the TF surface density resulted in condition-dependent differential acceleration of platelet deposition, thrombin formation, and fibrin accumulation. The viscous resistance of the clot was characterized by spatial variations and was higher in the inner clot region. Notably, despite variations in the intraclot structure, variations in the intraclot flow velocity were minor compared to the abrupt decrease in flow velocity at the boundary of the platelet deposition domain.

Our analysis revealed characteristic patterns that describe how the shape, size, internal structure, and viscous resistance of a clot depend on the surface density of TF and its area of exposure. Taken together, our results suggest that the structure and mechanics of a growing clot are correlated, but can differ in their regulation by the distinct aspects of TF localization. These findings provide new insights into how initiating signals can temporally and spatially affect thrombus growth under flow.

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