Inherent fibrin fiber tension propels mechanisms of network clearance during fibrinolysis

Abstract

Proper wound healing necessitates both coagulation (the formation of a blood clot) and fibrinolysis (the dissolution of a blood clot). A thrombus resistant to clot dissolution can obstruct blood flow, leading to vascular pathologies. This study seeks to understand the mechanisms by which individual fibrin fibers, the main structural component of blood clots, are cleared from a local volume during fibrinolysis. We observed 2-D fibrin networks during lysis by plasmin, recording the clearance of each individual fiber. We found that, in addition to transverse cleavage of fibers, there were multiple other pathways by which clot dissolution occurred, including fiber bundling, buckling, and collapsing. These processes are all influenced by concentration of plasmin utilized in lysis. The network fiber density influenced the kinetics and distribution of these pathways. Individual cleavage events often resulted in large morphological changes in network structure, suggesting that the inherent tension in fibers played a role in fiber clearance. Using images before and after a cleavage event to measure fiber lengths, we estimated that fibers are strained ~23% beyond their equilibrium length during polymerization. To understand the role of fiber tension in fibrinolysis we modeled network clearance under differing amounts of fiber polymerized strain (prestrain). The comparison of experimental and model data indicated that fibrin tension enables 35% more network clearance due to network rearrangements after individual cleavage events than would occur if fibers polymerized in a non-tensed state. Our results highlight many characteristics and mechanisms of fibrin breakdown, which have implications on future fibrin studies, our understanding of the fibrinolytic process, and the development of thrombolytic therapies.

Labeling fibrin fibers with microparticle sized beads alter single fibrin fiber lysis, external clot lysis, and produce large fibrin aggregates upon lysis

“…20 nm diameter FluoSpheres have frequently been used to label individual fibrin fibers during research [7,9,11,13,[26][27][28]. These studies do not consider the effect of fluorescent labeling on their results.…”

Citrullinated fibrinogen forms densely packed clots with decreased permeability

“…Because the fibers are not individually equilibrated onto the mica surface, fibers might be pre‐strained over their equilibrium length. 34 This inherent tension of the fibers could affect their apparent persistence length and the calculated Young's modulus. The calculated Young's modulus values reported here serve the purpose to compare the mechanical properties of the citrullinated fibrin sample to that of the control.…”

“…The Young's modulus of the fibers was calculated from the persistence length, using the second moment of inertia assuming circular fiber cross‐section. Because the fibers are not individually equilibrated onto the mica surface, fibers might be pre‐strained over their equilibrium length 34 . This inherent tension of the fibers could affect their apparent persistence length and the calculated Young's modulus.…”

Blood clot contraction: Mechanisms, pathophysiology, and disease

“…Reciprocally, endogenous fibrinolysis facilitates clot contraction both in vivo and in vitro , likely due to the partial cleavage of fibrin followed by reduction of clot stiffness [ 85 ]. In addition to the porosity and stiffness of the entire fibrin network, fibrinolysis depends strongly on the structure and properties of individual fibrin fibers, such as their mechanical tension, which impedes [ [86] , [87] , [88] ] or accelerates [ 89 ] fibrinolysis, depending on the conditions. Local concentrations and ratios of pro- and anti-fibrinolytic agents, their crosslinking to fibrin, and several other local and systemic factors that modulate clot contraction altogether determine whether contraction will slow down or quicken the cleavage [ [90] , [91] , [92] ].…”