(309c) Thrombus Growth and Embolism On Tissue Factor-Bearing Collagen Surfaces Under Flow Role of Thrombin with and without Fibrin

 At sites of vascular injury thrombin
is an important mediator in thrombus growth and stability. Using microfluidic
flow devices as well as patterned surfaces of collagen and tissue factor we
sought to determine the role that fibrin plays in clot stability without
interfering with the production of thrombin. We deployed an 8-channel
microfluidic device to study coagulation during corn trypsin inhibitor-treated
(XIIa-inhibited) whole blood perfusion over lipidated
tissue factor (TF) linked to a fibrillar collagen type 1 surface.  Clot growth and embolization were measured at
initial inlet venous (200 s^-1) or arterial (1000 s^-1)
wall shear rates under constant flow rate or pressure relief mode in the
presence or absence of Gly-Pro-Arg-Pro
(GPRP) to block fibrin polymerization.  
Numerical calculations for each mode defined hemodynamic forces on the
growing thrombi. In either mode at inlet venous flow, increasing amounts of TF
on the surface led to a modest dose-dependent increase (up to 2-fold) in
platelet deposition, but resulted in massive fibrin accumulation (> 50-fold)
only when exceeding a critical TF threshold. At a venous inlet flow, GPRP led
to a slight 20% increase in platelet accumulation (p < 0.01) in pressure
relief mode with thrombi resisting ~1500 s^-1 prior to full channel
occlusion. GPRP-treated thrombi were unstable under constant flow rate, where
shear forces caused embolization at a maximum shear rate of ~2300 s^-1
(69 dynes/cm²).   In constant
flow rate mode, the nonocclusive platelet-fibrin
deposits (no GPRP) withstood maximum shear rates of ~29,000 s^-1 (870
dyne/cm²) or ~95% of full channel occlusion.   For arterial inlet shear rate, embolization
was marked for either mode with GPRP present when shear forces reached 87 dynes/cm² (~2900 s^-1).  Under constant flow rate, platelet-fibrin
deposits (no GPRP) withstood maximums of 2400 dynes/cm² (80,000 s^-1)
or ~90% of full channel occlusion before embolization. Fibrin increased clot strength by 12 to 28-fold. Under pressure
relief mode, ~2-fold more fibrin was produced under venous flow (p < 0.001).
These studies define embolization criteria for clots formed with surface
TF-triggered thrombin production (± fibrin) under venous and arterial flows.

Figure 1 Whole blood (CTI 40 μg/mL)
in the presence or absence of 5 mM GPRP was perfused
over a fibrillar collagen surface at an initial arterial wall shear rate of
1000 s^-1, with (left, n=4) or without (right, n=8) pressure relief. Platelet
accumulation data was used to calculate the hemodynamic conditions at the
thrombus boundary based on simulation data.