.I. Biomechanics zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Vol. 27. No. I, pp. 35 42, 1994. OOZI-9290/94 $6.00+.00 Printed in Great Britain Pergamon Press Ltd zyxwvutsrqp LA TERA L MIGRATION OF BLOOD CELLS AND MICROSPHERES IN TWO-DIMENSIONAL POISEUILLE FLOW: A LASER-DOPPLER STUDY WIM S. J. UIJTTEWAAL, EVERT-JAN NIJHOF* and ROBERT M. HEETHAAR Department of Medical and Physiological Physics, University of Utrecht, The Netherlands zyxwvutsrqponmlkjihgfed Abstract-The inertia-induced lateral migration of rigid microspheres. platelets and erythrocytes is studied experimentally. The concentration and velocity profiles of the particles have been determined with a laser-Doppler anemometer designed for high resolution measurements. Data are compared with empiri- cal and analytical models on inertia-induced lateral migration of rigid spheres. Experiments done in rectangular flow channels of high aspect ratio reveal that at a sufficiently high particle Reynolds number, platelets exhibit tubular pinch effects comparable with those of rigid polystyrene microspheres. Eryth- rocytes also exhibit inertia-induced lateral migration at high particle Reynolds number and low medium viscosity. At a higher medium viscosity, erythrocytes show deformation-induced lateral migration towards the center of the flow channel. NOMENCLATURE particle radius area of the probe volume of the laser-Doppler anemometer width of the flow channel particle concentration average bulk particle concentration numerical constant in lateral velocity numerical constant in axial velocity k$k, values for zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA K obtained from our experiments, Karnis et al. (1966) and Tachibana (1973), re- spectively number of counted particles particle Reynolds number lateral position in flow chamber equilibrium position for tabular pinch lateral position for a particle at the entrance of the flow chamber time interval in concentration measurements sedimentation velocity lateral, and average lateral velocity axial, and average axial velocity axial position in the flow chamber reduced axial position in the flow chamber value of .Z,,/K obtained from the fitting procedure fluid viscosity wave length of light density. INTRODUCTION The inhomogeneous distribution of particles in flow in general, and of blood cells in particular, has re- ceived considerable attention since the availability of microscopic techniques. As soon as scientists were Received in final form 24 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA Marc h 1993. *Author to whom correspondence should be addressed at: Utrecht Biofysica Instituut, P.O. Box 80000, 3508 TA Utrecht, The Netherlands. able to observe the blood flow through capillaries, the inhomogeneous distribution of the red blood cells was discovered, but it was only in 1928 that Fihraeus obtained quantitative data on this phenomenon. He found that red blood cells tend to migrate towards the center of capillary flow tubes leading to a reduction in the average red cell concentration inside the tube compared with the discharge concentration, the so- called FIhraeus effect. Inhomogeneous distributions were also found in dilute suspensions containing model particles. Segrb and Sitberberg (1961, 1962) found lateral migration effects with macroscopic zigid spheres in Poiseuille flow. During the same period, experiments were reported on the lateral migration of deformable particles such as fluid drops and single red blood cells (Goldsmith, 1971; Goldsmith and Mason, 1962). Experimental data on the lateral migration of rods and discs are only known from Karnis et al. (1966). It is known that in blood flow through small tubes, platelets are expelled towards the tube wall as a result of the interaction with red blood cells, the so-called inverse FBhraeus effect (Eckstein et al., 1988; Tangel- der et al., 1985; Uijttewaal et al., 1993). In order to get an insight into the mechanisms driving the red cells to the core region of the flow tube and the platelets towards the tube wall, it is sensible to study the single components in highly diluted suspensions first. As mentioned above, the lateral migration of single red cells was studied in a few papers and appeared to be comparable with migration phenomena observed with fluid droplets in cases of low particle Reynolds numbers. The motion of single platelets is less well known but can be of great importance, especially if we consider that close to a vessel wall, in the red-cell depleted layer, the hydrodynamic interaction of plate- lets with the wall can have a great influence on the attachment of the platelets and the coagulation mech- anisms. Aarts et zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQ al. (1988) performed laser-Doppler 35