264203 Interstitial Permeation of Human Blood Clots Formed Under Flow Using Controlled Pressure Gradients in a Microfluidic Model of Bleeding

Wednesday, October 31, 2012
Hall B (Convention Center )
Ryan W. Muthard and Scott L. Diamond, Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA

Traumatic injuries and genetic bleeding disorders provide a sustained clinical need to understand the complex transport properties of intraluminal thrombi. We developed a microfluidic device to measure intraluminal thrombi permeabilities under controlled pressure gradients. Unlike many previous in vitro permeability methods, this device incorporates the critical mechanical and biological thrombi properties that can only be obtained under hemodynamic conditions. The PDMS microfluidic device maintains blood pressure and flow rate by utilizing two constant volume syringe pumps and a LabVIEW interface. The main channel is perfused with anti-coagulated human whole blood at an initial shear rate of 1100 s-1. After flowing blood contacts the localized collagen or collagen/lipidated tissue factor scaffold; the controlled pressure gradient forces blood to permeate through the structure. The pressure gradient is maintained by a downstream infusion of Ca2+ buffer controlled by LabVIEW and measured using three pressure transducers. Permeate velocity was measured using a pulse of texas red dye and a numerical model was employed to determine the permeabilities of the collagen scaffold, platelet layer, and platelet/fibrin layer. The device was validated by calculating a permeability of collagen (1.98x10-11 6.01x10-12 cm2) over varying pressures (12-23.4 mm Hg) and comparing to previous literature values. The resulting permeabilities for a platelet (5.45x10-14 9.66x10-15 cm2) and platelet/fibrin layer (2.71x10-14 3.56x10-15 cm2) formed over 10 minutes of flow provide insight into the relative resistance that each supply to the cessation of bleeding. Noticeably, the formation of fibrin and presence of thrombin provided a 50% reduction in permeability under hemodynamic conditions. In addition to permeability measurements, we observed decreased platelet accumulation with increased pressure drop (13.8-23.4 mm Hg) across the intraluminal thrombi in PPACK whole blood. This response can be explained by the increased permeation of ADP and TXA2 through the forming thrombi. The design and validation of our microfluidic device allowed for permeability measurements of intraluminal thrombi with and without thrombin. In the absence of thrombin, PPACK whole blood formed a platelet mass which was >350 fold less permeable than collagen alone. An additional 50% reduction of permeability was observed when thrombin was present and platelet/fibrin clots were formed.


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