Platelet plug microstructure and flow modulate fibrin gelation dynamics: Insights from computational simulations

During the formation of a thrombus, the architecture of the growing platelet aggregate is heterogeneous, with areas of dense and loosely packed platelets. The surface of activated platelets facilitate biochemical coagulation reactions that ultimately result in the formation of a fibrin network which stabilizes the thrombus. How platelet-plug microstructure and flow jointly govern the onset and development of fibrin is incompletely understood. We developed a novel 2D computational framework that integrates (1) a pre-adhered, discrete platelet aggregate, (2) a reduced coagulation model that generates thrombin, and (3) a fibrin polymerization model. Three platelet-plug configurations were constructed with prescribed interplatelet gaps and simulations were performed for each with various wall shear rates. We quantified spatiotemporal clotting metrics, including coagulation factor concentrations, fibrin evolution, and gelation onset. Across geometries, gelation initiation accelerated with increasing plug density. For more dense geometries, gelation emerged first near the plug periphery. As the platelet density increased, intraplug transport was increasingly restricted, particularly for fibrinogen and prothrombin, and the thrombin concentrations in the spaces between platelets increased. In contrast, the loose plug supported fibrinogen replenishment deeper into the plug core. Thus, despite slower coagulation initiation due to reduced platelet surface area, monomer generation persisted further into the interior, causing gelation to begin at the vessel wall instead of the periphery. For all plug densities, fibrin ultimately filled the plug within the simulated time frame, while increasing shear reduced the gel-covered area outside the plug. These results suggest a mechanistic tradeoff: rapid sealing of the injured vessel wall by early platelet contraction, i.e. plug densification, may impede the intraplug fibrin formation needed for durable stabilization. The proposed model provides a basis for systematic studies of platelet-coagulation interactions under flow, including extensions toward therapeutic developments relevant to prevention of cardiovascular disease.