A microscopic evaluation of the influence of fluid dynamics on the clotting of a blood analog fluid

Abstract number: P1853

Martin A., Christy J. R. E.

University of Edinburgh, UK

The object of this work was to determine the effects of different flow regimes on clot formation in renneted milk, for microscopic evaluation of its suitability as a blood analogue fluid for assessing flow-induced thrombosis of artificial heart valves. Since mechanical heart valves generate varying degrees of shear stress and regions of stasis in the blood, it was desirable to determine the effects of these flow parameters on milk clotting. A stagnation point flow chamber was produced to generate similar flow conditions to those used elsewhere for testing whole blood and platelets [1, 2]. Stagnation point flow involves the impingement of a jet of fluid onto the underside of a microscope coverslip, allowing continuous monitoring of adhesion and aggregation under known flow conditions. For the current work, skim milk was used to minimize the effects of fat globules and improve visibility of the clot progression. Prior to entering the flow chamber, the milk was mixed with 1% vol saturated aqueous calcium chloride and 1% vol rennet to initiate the clotting reaction. Clot development was monitored for 30 min with either an optical microscope or a confocal scanning laser microscope and photographed throughout the reaction with a digital camera. Clot morphology was found to depend largely on the flow regime. At the stagnation point, a discreet clot of limiting radius adhered to the coverslip, similar to that seen elsewhere in thrombus formation [1, 2]. At the outer edge of the flow chamber, a clot developed which blocked further flow into this region. This clot grew inward, and was of a striated nature, rather different from the clot formed over the stagnation point. Finally, between the two aforementioned clots, there was a flow channel, above which a sparse, speckled clot ultimately developed. These results confirm that milk clot development and structure are affected by fluid dynamics. Further microscopic work is being carried out to determine the extent of this similarity between flow-induced milk clotting and flow-induced thrombosis.

1  Petschek, H, Adamis, D & Kantrowitz, AR. (1968) Stagnation flow thrombus formation. ASAIO Trans. 14, 256.

2  Reininger, AJ, Reininger, CB & Wurzinger, LJ. (1993) The influence of fluid dynamics upon adhesion of ADP-stimulated human platelets to endothelial cells. Thromb Res. 71, 245.