Morphological study of platelet adhesion dynamics under whole blood flow conditions

A flow system consisting of a parallel-plate flow chamber mounted on the epifluorescence video microscope has been constructed to allow direct visualization of the entire platelet adhesion process under whole blood flow conditions. Adhered platelets with recorded adhesion history were individually identified and observed in detail using a scanning electron microscope. In this study we used cover glasses coated with fibrinogen, fibrin, or collagen as the testing surface. From experiments carried out at the surface shear rate of 445 s(-1), we found that (1) platelet adhesion was a dynamic process that involved attaching, detaching, relocation and transient contact; (2) platelets adhered to all three types of protein-coated surfaces with platelet adhesion on collagen being most unstable; (3) most of these adhered platelets immediately formed short pseudopods after surface contact; (4) platelets adhered to fibrinogen or fibrin were basically non-overlapping and they underwent further shape change with increasing number /length of pseudopods and increasing extent of cytoplasmic spreading; (5) on collagen-coated surface most incoming platelets attached to previously adhered platelets rather than to the collagen threads for blood-surface contact times longer than 30 s; (6) these platelets formed multicellular thrombi with largest thrombi located at about 0.2-0.4 mm from the upstream edge and (7) platelets in the thrombi formed numerous short pseudopods and started fusing with one another within 2 min. These observations show that platelet adhesion under blood flow is a complex and dynamic process and that adhered platelets undergo heterogeneous post-contact morphological changes. Moreover, our results indicate that fibrinogen and fibrin coatings are adhesive while collagen coating is most stimulatory to platelets.