Deformation of erythrocytes and aggregates during sedimentation under microgravity.

The basic unit of an aggregate is an erythrocyte which possesses viscoelastic properties. To determine the changes in the shape of erythrocytes during sedimentation in microgravity field the present work is carried out. Fresh well mixed erythrocytes suspensions in plasma at 8% hematocrit are placed in a glass chamber. The entire experimental setup is mounted in a module and placed in a capsule. The online data on the sedimentation of the cells under normal and microgravity are recorded by a video microscopic system. The data are analysed by a PC/AT based image processing system. The results show that the erythrocyte undergoes a process of shape deformation and its sedimentation velocity decreases during microgravity. The erythrocyte from a nearly elliptic shape is transformed to nearly circular shape. A similar change in the projected area of the aggregate is also observed. This is further supported by a varying pattern of sedimentation velocity from normal to microgravity duration. The observed change in the erythrocyte membrane may contribute in the loosening of the large aggregates leading to formation of smaller size aggregates.