Visualization of erythrocyte deformation induced by supraphysiological shear stress.

To elucidate development of shear-induced damage in erythrocytes, it is necessary to visualize erythrocytes under high-shear flow. Therefore, we prototyped a special shear flow chamber with a counter-rotating mechanism consisting of a transparent acrylic cone and a glass plate. The flow chamber was mounted on an inverted microscope and illuminated by a 350-W metal halide lamp. This experimental system made it possible for a digital video camera to record through the microscopes' objective lens the rheological behavior in shear flow of erythrocytes diluted in highly viscous polyvinyl pyrrolidone. We successfully visualized the blood cells' ellipsoidal deformation response to an unphysiological, high shear stress of 288 Pa, their shift into abnormal rheological behavior, and final collapse. When abnormality first appeared, the membrane surface of some ellipsoidal erythrocytes started undulating and their shape became more asymmetric. Finally, the erythrocytes appeared to fragment, although the fragments continued tumbling together suggesting that they were all still connected. One such abnormal erythrocyte became segmented through collision with other cell. The undulation of the membrane surface when erythrocytes experienced trauma suggests possible detachment of the lipid bilayer from the membrane cytoskeleton. As the damage increased, the morphological abnormality of cells became greater with less tank-treading, and then, the erythrocytes started tumbling. This unstable behavior increases the volume of flow region occupied by the erythrocytes and increases the chance that neighboring cells will hit them and break them into segmented pieces. This study clearly showed that the beginning of erythrocytes' morphological abnormality was induced by shear stress.