Effect of shear stress on platelet adhesion to expanded polytetrafluoroethylene, a silicone sheet, and an endothelial cell monolayer

We visualized in real-time platelets adhering to the surface of three repre sentative biomaterials, by using an apparatus consisting of a modified cone and plate rheometer combined with an upright epifluorescence microscope un der two shear flows (0.1 and 5.0 dyne/cm(2)). The materials were expanded p olytetrafluoroethylene (ePTFE), silicone sheet, and a monolayer of bovine e ndothelial cells (ECs) formed on glass, all of which are opaque materials u sed for artificial blood vessels and medical devices. According to quantita tive analysis, the monolayer of ECs formed on glass had better blood compat ibility than did either the ePTFE or the silicone sheet under shear flow co nditions. Under a shear flow condition of 0.1 dyne/cm(2), platelet adhesion was silicone sheet > ePTFE. In contrast,under a shear flow condition of 5. 0 dyne/cm(2), ePTFE > silicone sheet. These results indicate that the inten sity of shear stress could modify the order of hemocompatibility Of the mat erials. Therefore, direct observation of platelet adhesion under shear flow conditions is indispensable for testing and screening biomaterials and for providing a precise quantitative evaluation of platelet adhesion.