Rheology of fibrin clots. IV. Darcy constants and fiber thickness.

Measurements of small oscillatory deformations of a fibrin clot by axial motion of a rod in a closed tube reveal an anomalous mechanical loss due to permeation of fluid through the clot structure. The Darcy constant for permeation can be calculated from data at the frequency where the apparent storage and loss shear moduli are equal, without the necessity of measurements at much lower frequencies as previously employed. From the Darcy constant, the average number of fibrin monomer units (v) per cross-section of a fibrous element of the clot can be calculated; it ranges from 4 to several hundred. In the range of fibrin concentration(c) from 3 to 14 milligrams, v is approximately proportional to c-2 for clots of coarse structure and to c-0.5 for clots of fine structure.