Even though blood pumps have come into clinical usage, thrombo-embolic complications still pose a major problem, and they have not yet been clarified and quantified. However, it is known that the basis of thrombus formation is platelet adhesion, which is thought to be closely associated with the shear rate. Therefore, our current interest focuses on the effect of shear conditions on platelet adhesion. We have designed and carried out an experimental setup allowing fluorescent microscopy of whole blood within a rotational viscometer under controllable shear conditions. A small area of the bottom plate was coated with type I collagen, which provided a model of the injured vessel as a target for platelet adhesion. Using this setup, the time course of platelet adhesion under several different shear rates, ranging from 127 to 723 s -1, was studied. Platelet adhesion increased along with shear rates up to 283 s -1, followed by a gradual decrease when the shear rate exceeded 346 s -1. The adhesion amounts were statistically significant between 283 and 173 s -1 (p = 0. 02), 173 and 127 s -1 (p = 0. 035), and 283 and 503 s -1 (p = 0. 03), respectively. This result suggests that there is an optimal shear condition around 300 s -1 for platelet adhesion to type I collagen.
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