Summary
Although many in vitro fibrin studies are performed with plasma, in vivo clots and thrombi contain erythrocytes, or red blood cells (RBCs).To determine the
effects of RBCs on fibrin clot structure and mechanical properties, we compared plasma
clots without RBCs to those prepared with low (2 vol%), intermediate (5-10 vol%),
or high (≥20 vol%) numbers of RBCs. By confocal microscopy, we found that low RBC
concentrations had little effect on clot structure. Intermediate RBC concentrations
caused heterogeneity in the fiber network with pockets of densely packed fibers alongside
regions with few fibers. With high levels of RBCs, fibers arranged more uniformly
but loosely around the cells. Scanning electron micrographs demonstrated an uneven
distribution of RBCs throughout the clot and a significant increase in fiber diameter
upon RBC incorporation. While permeability was not affected by RBC addition, at 20%
or higher RBCs, the ratio of viscous modulus (G′′) to elastic modulus (G′) increased
significantly over that of a clot without any RBCs. RBCs triggered variability in
the fibrin network structure, individual fiber characteristics, and overall clot viscoelasticity
compared to the absence of cells. These results are important for understanding in vivo clots and thrombi.
Keywords
Blood coagulation - confocal microscopy - erythrocyte - fibrin - fibrin network