Nonlinear relationships of fibrin network structure as a function of fibrinogen and thrombin concentrations for purified fibrinogen and plasma clots

Background: Fibrinogen levels are associated with bleeding disorders and thrombotic disease. Thrombin converts fibrinogen to fibrin, producing the load-bearing fibrin scaffold that governs clot mechanics and transport. Objective: Quantitatively map how initial fibrinogen and thrombin concentrations, [ F g n ] 0 and [ T h r ] 0 , determine fibrin architecture in human plasma and a purified fibrinogen system. Methods: Scanning electron microscopy was used to quantify single-fiber morphology—fiber diameter and branch-to-branch segment length from a standardized sample-preparation protocol. Confocal microscopy was used to quantify network architecture—projected fiber density and pore/bubble size. Results and Conclusions: Across plasma and purified systems, fibrin structural parameters were quantitatively captured by compact multiplicative scaling laws of the form Y = k [ F g n ] 0 α [ T h r ] 0 β . Unlike prior studies, which examined narrower condition ranges without establishing predictive equations across a systematic fibrinogen–thrombin concentration matrix, this framework defines distinct, quantitative roles for fibrinogen and thrombin in fibrin assembly. The magnitudes and signs of the exponents α and β indicate that thrombin primarily controls individual fiber growth kinetics, strongly shortening branch-to-branch segment length and modestly thinning fibers, whereas fibrinogen primarily controls space filling, strongly increasing fiber density, reducing pore/bubble size, and thickening fibers. For matched [ F g n ] 0 and [ T h r ] 0 , compared to plasma clots, purified fibrinogen formed denser networks with thinner and shorter fibers, suggesting that the plasma biochemical environment partially inhibits thrombin activity. Fiber length analysis further suggests that each thrombin molecule nucleates one fiber segment. Together, these parameterized scaling relations provide a predictive quantitative framework linking clot composition to fibrin microstructure in plasma and purified fibrinogen clots. Statement of Significance The research describes a comprehensive and internally consistent characterization of how fibrinogen and thrombin jointly shape fibrin network structure, the scaffold of blood clots. A broad set of structural features are well described by compact, multiplicative power laws Y = k [ F g n ] 0 α [ T h r ] 0 β . These parameterized scaling relations allow predictions that link composition to fibrin microstructure. Fiber length analysis suggests a new mechanism for fibrin network growth, in which each thrombin molecule nucleates one fiber. These relationships provide the baseline for extensive, quantitative modeling work of blood clotting. This work indicates that thrombin primarily controls single-fiber growth kinetics, strongly shortening branch-to-branch segment length and modestly thinning fibers, whereas fibrinogen primarily controls space filling, strongly increasing fiber density and reducing pore/bubble size while thickening fibers.