Shapes and dimensions of blood clots affect the rate and extent of platelet-driven clot contraction and determine the outcomes of thrombosis.

BACKGROUND

Contraction of blood clots has multiple pathophysiological implications.

OBJECTIVES

To determine whether the initial shape and dimensions of blood clots affect clot contraction.

METHODS

Thrombin-induced clots of various sizes were formed in human blood or platelet-rich plasma in a cylinder, cuboid, or flat chamber. Clot shrinkage was tracked photographically. After complete contraction, the physiologically most relevant cylindrical clots of various initial volumes were analyzed with scanning electron microscopy for composition and spatial nonuniformity with the emphasis on compressed polyhedral erythrocytes (polyhedrocytes).

RESULTS

With the same volumes studied, the final extents of contraction of 0.3-mL whole blood clots were shape-dependent, such that flat was more contracted than cylindrical, which was equal to cuboid. Irrespective of the shape, the smaller clots mainly contracted to a larger extent. Unlike whole blood clots, platelet-rich plasma clots contracted independently of the clot volumes and shapes studied, indicating a key role of erythrocytes. The smaller blood clots contained more erythrocytes, especially polyhedrocytes, due to tight packing and a decrease in the intercellular space. The spatial segregation within the larger clots was less marked than in the smaller clots, reflecting incomplete spatial redistribution of blood clot components typical for robust contraction.

CONCLUSION

Contraction of blood clots depends on their shape and size. The smaller and larger clots have distinct size-dependent rates and extents of contraction as well as degrees of structural nonuniformity, reflecting different spatial gradients of compressive stresses. These findings are relevant to the variable geometry and size of intravascular blood clots and thrombi.