Clots are a three-dimensional network of fibrin fibers, stabilized by another protein called factor XIIIa. A blood clot needs to have the right degree of stiffness and plasticity to stem the flow of blood when tissue is damaged, yet be digestible enough by enzymes in the blood so that it does not block blood-flow and cause heart attacks and strokes.
Weisel and colleagues developed a novel way to measure the elasticity of individual fibrin fibers in clotswith and without the factor XIIIa stabilization. They used "laser tweezers"essentially a laser-beam focused on a microscopic bead 'handle' attached to the fibersto pull in different directions on the fiber.
The investigators found that the fibers, which are long and very thin, bend much more easily than they stretch, suggesting that clots deform in flowing blood or under other stresses primarily by the bending of their fibers.
Weisel likens the structure of a clot composed of fibrin fibers to a microscopic version of a bridge and its many struts. "Knowing the mechanical properties of each strut, an engineer can extrapolate the properties of the entire bridge," he explains. "To measure the stiffness of a fiber, we used light to apply a tiny force to it and observed it bend in a light microscope, just as an engineer would measure the stiffness of a beam on a macroscopic scale. The mechanical properties of blood clots have been measured for many years, so now we can develop models to relate in
Contact: Karen Kreeger
University of Pennsylvania School of Medicine