Background: Fibrin is a unique biomaterial and a major component and mechanical determinant of hemostatic blood clots and obstructive thrombi.

Aims: Here, we explored the rupture of blood clots, emulating thrombus breakage by stretching fibrin gels with single-edge cracks.

Methods: We employed tensile testing to collect the force-displacement response of fibrin gels with controlled defects, and scanning electron microscopy and transmission electron microscopy to visualize fibers rupture

Results: The stress-strain profiles display the weakly non-linear regime I of the gel due to alignment of fibrin fibers; linear elastic regime II owing to reversible stretching of fibers; and the rupture regime III for large deformations, during which irreversible breakage of fibers occurs. These dynamic mechanical regimes correlate with structural changes in the fibrin network. To model the stress-strain curves, we developed the Fluctuating Spring model, which maps the fibrin alignment, elastic network stretching, and cooperative rupture of coupled fibrin fibers into a theoretical framework to calculate stress as a function of strain.

Conclusions: Cracks render network rupture stochastic. The free energy change for fiber deformation and rupture decreases with the crack size, thereby making the network rupture more spontaneously, but mechanical cooperativity due to the inter-fiber coupling strengthens the fibrin network. These results provide a basis for understanding of blood clot breakage that underlies thrombotic embolization. The Fluctuating Spring model can be used to characterize the dynamics of mechanical deformation of other protein networks.

Panel A: Snapshots of fibrin gel sample (30 mm × 30 mm × 6.5 mm) with a 12-mm single-edge crack at the times that correspond to the dynamic mechanical regimes I-III. Panel B: Stress-strain and slope-strain profiles showing non-linear regime I of deformation due to fibrin fibers alignment at the characteristic strain, linear regime II of elastic deformation due to fibers stretching, and rupture regime III due to fibers rupture at the strain threshold. The critical stress of 1.53 kPa and critical strain of 31% are attained when all fibers have ruptured.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/biomechanics-thermodynamics-and-mechanisms-of-rupture-of-fibrin-clots/