Concentration profiles of platelet-sized latex beads for conditions relevant to hollow-fiber hemodialyzers.

A freeze-capture method was used to obtain the concentration profiles of platelet-sized latex beads (2.5 microns diameter) in saline-based red cell suspensions flowing through tubes with inner diameters of 135 and 200 microns. Without red cells the concentration profile exhibited a slight deficit near the wall. For hematocrits from 15 through 52%, the concentration profile exhibited a near-wall excess of beads, from two to eight times the central concentration. Near-wall excesses were small or nonexistent in the first half centimeter of the tube. For hematocrits of 15 and 30%, the profile and near-wall excess were equal at stations 2 cm or more from the entrance. These results suggest that there is a flow-driven mechanism that moves platelet-sized beads toward, but not to, the wall.