Assistant Professor Rutgers-State University of New Jersey, United States
Introduction:: Fibrin is a naturally occurring biomaterial that provides mechanical and structural stability to blood clots (thrombi). Previous studies have shown that altering the coagulation activators (thrombin or tissue factor) concentration has a significant impact on the structure of the fibrin clot. Further, the local fibrin network structure is altered in hypercoagulable state and impacts the mechanical response of blood clots under dynamic conditions. Patients with hypercoagulable states are associated with risk for thrombotic conditions such as heart attacks and strokes. Embolization, or rupture of a thrombus, is a complication of thrombosis that increases mortality risk by up to 30%. In addition, fibrin has many biomaterial applications.
Materials and Methods:: We performed single edge notch fracture tests to examine fibrin rupture under a constant strain rate (Figure 1A) with varying tissue factor (TF) concentrations using a Biomomentum mechanical tester. Using this data we assessed fracture toughness, maximum strain and maximum force prior to rupture. We utilized confocal and scanning electron microscopy to quantify the fibrin network structure under varying TF concentration both before and during rupture process. Parameters assessed included density, diameter, and pore size.
Results, Conclusions, and Discussions:: Our results revealed that increasing TF concentration (30-600pM) yields a bell-shaped distribution of fracture toughness with a maximum of 7 N/m peaking at 75pM TF concentration (Figure 1B). Low (30pM) and high (600pM) TF concentration showed a significantly lower toughness when compared to 75pM samples (p< 0.0001 and p< 0.01 respectively). Correlation analysis revealed no dependence of toughness on initial crack lengths across all TF concentrations studied, demonstrating that toughness is a well-defined material parameter. Increased TF concentration resulted in increased fibrin density (16-23 fiber pixels/total voxel (%), p< 0.0001) (Figure 1B), and thinner (150-75 nm, p< 0.0001) (Figure 1C), shorter (16-7 µm, p< 0.0001) fibrin fibers with a reduction in pore size (6.5-3 µm, p< 0.0001). Our results suggest that fibrin diameter and density play a bimodal role in influencing the rupture resistance of blood clots (Figure 1C), pointing to a critical local TF concentration and thus that fibrin structure drives the mechanical response of the fibrin fibers. These findings add to our understanding of the structure-function relationship in 3-D fibrin network by elucidating the influence of structural characteristics on the fibrin mechanical response. These results provide a basis for understanding and predicting the tendency for thrombotic embolization and can be applied to developing improved scaffolds for tissue engineering.
