THE EFFECT OF SHEAR ON OLIGOMER FORMATION; EFFECTIVE REMOVAL OF MONOMERS

Fibrin polymerization has been found to be influenced by shear flow conditions (Puryear,1980). In order to determine which mechanisms are responsible for theeffect reported it is necessary to look at the various stages in fibrin polymerization. It is known that the enzymatic attack of thrombin on fibrinogen is not influenced by shear (Sellers,1981). The next step, which is investigated in this study, is the oligomer-early protofibril stage.

Fibrinogen (human, Kabi) is reacted with thrombin (human, Sigma) under Couette flow conditions (volume-averaged shear 0-250sec-l) in a pH 6.8, 4mM CaC12, HEPES buffered solution (I. S.-.15). The reaction time is chosen so that 6% of fibrinopeptide A (FPA) is released. The reaction is stopped by a 1,6 hexandiol-hirudin solution. The effect of shear on oligomer population is measured using large angle 1ightscattering techniques.

In order to predict theoretical shear effects on oligomer formation, it is important to be able to predict the population size. This is done using Jamney’s (1983) predictions, for early reaction time, assuming q=16. Given a size distribution it is possible to apply low Reynold’s number hydrodynamic and Smoluchowski1 s( coagulation theories to predict possible shear affects.

Hydrodynamic theory predicts no effect of shear on oligomer formation; Peclet numbers are too small. Smoluchowski coagulation theory, on the other hand, predicts that for oligomer sized particles in the shear range studied, orthokinetic (shear induced) coagulation becomes more important than peri kinetic (Brornian) coagulation.

Results obtained from Zimm analysis show a dramatic increase in molecular weight, compared to the stagnant case, in the shear region corresponding to where orthokinetic coagulation dominates. The higher the thrombin concentration, the more extreme and earlier (i.e. lower shear) these effects are felt. After a peak is reached in molecular weight there is a sudden drop. This is caused by monomer exhaustion which shifts the population to a more homogeneous type. The concept of orthokinetic coagulation is important physiologically since it is advantageous to incorporate monomers onto fibers as quickly as possible.