Contact activation of blood coagulation on a defined kaolin/collagen surface in a microfluidic assay

Abstract

Generation of active Factor XII (FXIIa) triggers blood clotting on artificial surfaces and may also enhance intravascular thrombosis. We developed a patterned kaolin (0 to 0.3pg/μm2)/type 1 collagen fibril surface for controlled microfluidic clotting assays. Perfusion of whole blood (treated only with a low level of 4μg/mL of the XIIa inhibitor, corn trypsin inhibitor) drove platelet deposition followed by fibrin formation. At venous wall shear rate (100s−1), kaolin accelerated onset of fibrin formation by ~100sec when compared to collagen alone (250sec vs. 350sec), with little effect on platelet deposition. Even with kaolin present, arterial wall shear rate (1000s−1) delayed and suppressed fibrin formation compared to venous wall shear rate. A comparison of surfaces for extrinsic activation (tissue factor TF/collagen) versus contact activation (kaolin/collagen) that each generated equal platelet deposition at 100s−1 revealed: (1) TF surfaces promoted much faster fibrin onset (at 100sec) and more endpoint fibrin at 600sec at either 100s−1 or 1000s−1, and (2) kaolin and TF surfaces had a similar sensitivity for reduced fibrin deposition at 1000s−1 (compared to fibrin formed at 100s−1) despite differing coagulation triggers. Anti-platelet drugs inhibiting P2Y1, P2Y12, cyclooxygenase-1 or activating IP-receptor or guanylate cyclase reduced platelet and fibrin deposition on kaolin/collagen. Since FXIIa or FXIa inhibition may offer safe antithrombotic therapy, especially for biomaterial thrombosis, these defined collagen/kaolin surfaces may prove useful in drug screening tests or in clinical diagnostic assays of blood under flow conditions.