[9] Platelet interaction with artificial surfaces: in vitro evaluation

This chapter describes the in vitro evaluation of platelet interaction with artificial surfaces. The glass-bead-column method allows surface-induced platelet adhesion, aggregation, and secretion to be examined for any material that can be prepared in a bead form or coated onto glass beads by deposition from solution. Bead columns are exposed to flowing whole blood, anticoagulated with sodium citrate, and maintained at 37° temperature. Platelet retention is determined by comparing the number of platelets entering and leaving the columns. Platelet secretion is assayed by measuring extracellular serotonin and β-thromboglobulin levels in the effluent blood. Platelet lysis is monitored by measuring extracellular lactate dehydrogenase levels, and the relative effects of adhesion and aggregation are assessed by scanning electron microscopy. The passage of blood through columns packed with small polymer-coated glass beads is a severe test of platelet–surface compatibility because of the large surface area to blood volume ratio. A 2-mL column packed with 0.3-mm-diameter beads provides ∼300 cm2 of surface area, which, at a point in time, is exposed to ∼0.5 mL of blood. This is equivalent to spreading a film of blood 17 pm thick on a flat surface and represents approximately one-tenth of the surface-to-volume ratio of a capillary bed.