Modification of shear modulus and creep compliance of fibrin clots by fibronectin

Shear moduli and creep compliances have been measured for four types of clots of human fibrin (about 7 $\text{mg}\text{ml}$) clotted with and without human plasma fibronectin (usually 1.2 $\text{mg}\text{ml}$). Fine clots (with little lateral aggregation of the fibrin protofibrils) were formed at pH 8.5, ionic strength 0.45 ; coarse clots (with substantial lateral aggregation) were formed at pH 7.5, ionic strength 0.15; in both cases with and without ligation by fibrinougase. In fine clots, the addition of fibronectin without ligation scarcely affected the shear modulus; with ligation, the modulus was decreased by a factor of 0.48. In coarse clots, the shear modulus was increased by addition of fibronectin. The increase was by a factor of 2.0 without ligation and by a factor of 2.4 with ligation. Creep and creep recovery in clots formed with and without fibronectin were similar except for the scale factor represented by the change in modulus.