When red blood cells are centrifuged, the cells gather in red “stripes” from the top (low density) to the bottom (high density), with white stripes with fewer red blood cells in between. Until now, it was assumed that this was due to the irregular loss of water that the blood cells suffer over time. Physicists from Saarland University and Bristol University have now been able to refute this assumption. They were able to prove that the blood cell strips are much more caused by their own attraction and adhesion to their neighboring cells.

The finding: It is the sheer number of cells that leads to the formation of stripes. “The stripe pattern is only created by the interaction of a large number of cells. In the experiment, there were around one billion in a tube,” says doctoral student Felix Maurer. After reducing the number of cells, the physicists were able to observe a completely different behavior: “Without aggregation, i.e. gluing cells together, the cells are evenly distributed everywhere, no streaks are formed,” explains Maurer.

It is therefore the interaction of aggregation, the accumulation of many cells in a small space, and opposite gravity that causes the blood cells to form the typical stripe pattern. These fundamental findings could, for example, be an important basis for the development of new diagnostic approaches for diseases of the blood, such as sickle cell anemia, in the course of which blood cells deform and their flow and agglomeration behavior changes accordingly. “In sickle cell anemia, for example, there is an altered stripe pattern, as a 2021 study showed. Until now, however, it has not been possible to explain why this was the case,” says Maurer.

A second fundamental aspect that the study sheds light on is the question of how patterns and structures arise in nature in the first place. To this end, Felix Maurer, Alexis Darras and their colleagues have derived a mathematical model based on the so-called dynamic density functional theory from their observations in the laboratory, which can explain such pattern formation. “An equation similar to the one we have now developed in our study also describes the patterns of zebra crossings, flocks of birds and fingerprints,” says Christian Wagner. Felix Maurer explains what this is all about: “In our case, a short-range interaction between individual cells leads to the development of a preferred macroscopic strip width and a preferred stripe spacing. Flocks of birds also show collective behavior. There, the formations are created from simple neighborhood rules between individuals. There is a similar idea in the creation of fingerprints.”

Original Paper:

Band pattern formation of erythrocytes in density gradients is due to competing aggregation and net buoyancy | PNAS

Editor: X-Press Journalistenbüro GbR

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