Interaction of Platelets with Surfaces: A Factorial Study of Adhesion and Associated Release of Serotonin

Adhesion of platelets to several polymer surfaces and the release of serotonin from adherent platelets have been investigated. The platelets were washed, labelled with 51Cr and 14C-serotonin and suspended in media containing different concentrations of red cells, albumin and fibrinogen. The apparatus was a couette flow device operated under well-characterised flow and transport conditions. Adhesion and release were measured by counting radioactivity of both isotopes on the surface and comparing to aliquots of suspension of known platelet concentration. A factorial experimental design was used to obtain estimates of the effects of haematocrit, platelet count, fibrinogen concentration and albumin concentration on adhesion and release. This approach also allowed estimates of the effects of the different surfaces, independent of any of these ‘environmental’ factors. The surfaces studied formed a series of segmented poly-ether urethanes and glass. Adhesion was found to be strongly dependent on the surface properties and decreased with increasing hydrophilicity of the polyurethanes. Release was somewhat less dependent on surface properties but increased with increasing hydrophilicity. The most important environmental factors for adhesion were haematocrit and fibrinogen concentration, both of which caused an increase. For release, haematocrit and fibrinogen were also important. However, release was found to decrease as the levels of these factors increased. Thus, the effects of surface properties and environmental factors were found to be opposite for the adhesion and release response.