Staying on Track: Collagen Fibers Orientation Strongly Affects Thrombi Formation at High Shear

Subendothelial matrix exhibits a distinctive organization, with collagen fibers beneath the endothelium oriented parallel to the flow and comprising mainly types III and I collagen in arteries and arterioles. However, the significance of such organization in initiating thrombus formation remains unclear.To investigate the role of collagen fibers orientation in triggering platelet plug formation, we utilized an in vitro microfluidic model of thrombosis. Human whole blood was perfused over collagen fibers oriented either perpendicular (transverse) or parallel (lengthwise) to the flow. Primary stages of platelet adhesion and aggregate growth were analyzed using high-speed fluorescence microscopy.At shear rates of 200 and 1,000 s^-1, collagen fibers orientation had no significant effect. However, at a high shear rate of 2,000 s^-1, aggregates on lengthwise fibers were higher and covered a larger area than those on transverse ones. High-speed microscopy revealed that platelets adhered stably only after interacting with the surface for several seconds under all studied conditions. Analysis of single platelet dynamics revealed longer interaction times and greater translocation distances on lengthwise fibers, suggesting that these fibers facilitate stable adhesion by enabling extended contact with collagen during translocation. Notably, only a small fraction of collagen fibers belonging to the type III collagen admixture in a standard type I collagen preparation accumulated plasma vWF and supported platelet translocation at a high shear rate.Type III lengthwise collagen fibers promote platelet translocation and stable adhesion at high shear rates, which may be relevant for triggering thrombus formation in vivo.