Oriented Fibrin Gels Formed by Polymerization in Strong Magnetic Fields

Fibrinogen is a soluble plasma protein which, after cleavage by the specific proteolytic enzyme thrombin, polymerizes to form the filamentous fibrin network during blood clotting (see refs 1 and 2 for reviews). Fibrinogen has a molecular weight of 340,000 and is composed of two identical halves, each containing three peptide chains designated A alpha, B beta and gamma. Fibrin monomers are produced by thrombin which releases the small negatively charged fibrinopeptides A and B. The overall shape of the fibrinogen molecule has not been unequivocally established. The trinodular, elongated (approximately 450 A long) structure proposed by Hall and Slayter is the most widely accepted model and it has obtained additional support from recent work. Fibrin monomers are also about 450 A long and in fibres they probably have a half-staggered arrangement along the axis. The fibres are an assembly of protofibrils whose structure and packing are not reliably known. We report here that highly oriented fibrin gels are formed when polymerization takes place slowly in a strong magnetic field. It is shown that the protofibrils pack into a three-dimensional crystalline lattice. We introduce magnetically induced birefringence as a potential tool for studying polymerization and briefly speculate on the applications of strong magnetic fields.