Platelet reactions to modified surfaces under dynamic conditions

The influence of surfaces on the reactions of platelets in whole blood unde r laminar flow was investigated in a cone and plate viscometer. Citrated wh ole blood was exposed to steel, PMMA and PMMA modified with PEO at low (500 s(-1)) and high (4000 s(-1)) wall shear rates at room temperature for a pe riod of 100 s. Treated blood samples were fixed with paraformaldehyde, stai ned with a monoclonal antibody for CD41 (platelet GPIIb/IIIa) conjugated wi th phycoerythrin and analyzed by flow cytometry. The reactions of platelets (microparticle generation and formation of platelet-platelet, platelet-red blood cell and red blood cell-microparticle aggregates) to these environme nts were quantified. Additionally, the size of platelet-platelet aggregates was assessed. The percentage platelet aggregation and numbers of micropart icles generated were independent of surface type at any shear rate. The com position of the aggregates formed was influenced by the surface: at low and high shear rates PMMA caused the generation of platelet-platelet aggregate s of the greatest size. The numbers of red blood cell-platelet and red bloo d cell-microparticle aggregates also varied depending on the surface. Fewer red blood cell-platelet aggregates were formed at higher shear rates, wher eas the reverse was true for red blood cell-microparticle aggregates. It is concluded that these variations may help to explain the differential effec ts of surfaces to the induction of distant thrombotic events: microparticle s may be protected from loss from the blood stream by their association wit h red blood cells at high shear rates. (C) 1998 Kluwer Academic Publishers.