The dynamic rigidity of fibrin gels1

The dynamic rigidity and loss modulus of the solutions of fibrinogen with added thrombin have been determined by a viscoelastorecorder throughout the period of gelation. The rigidity of the fibrin gel is approximately proportional to the square of the concentration of fibrinogen. The dynamic rigidi ty of the fibrin gel depends upon the amplitude and frequency of oscillation applied during gelation. The logarithms of the rigidity and loss moduli decrease linearly with the square root of the dynamic shear rate, i.e. the angular frequency times amplitude. The mechanical agitation during gelation prevents the sufficient formation of the fibrin network. When the gelation of fibrin is completed under a certain large amplitude of oscillation and the measuring amplitude is decreased from that given during gelation, the decrease of the rigidity modulus is observed, which suggests that the fibrin molecules between crosslinks of the network are fairly stretched by the applied strain during gelation. The kinetic analysis of the clotting curves also indicates that the gelation is caused by the crosslinks between fibrin polymers and by the stretching of the fibrin molecules between crosslinks.