Blood: Mini-forces determine flow resistance

For the first time, physicists calculate the influence of the attraction between red blood cells on the flow behavior of blood

Hardly imaginable is the attraction that red blood cells exert on one another: a team of just about three to seven Pico-Newton (trillionth of Newton) was calculated by the physicist Gerhard Gompper. © Forschungszentrum Jülich
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Red blood cells attract each other. But the forces involved are ten million times smaller than those caused by the weight of a sitting mosquito. Nevertheless, these forces determine the flow resistance of blood, as a German-American physics team could now show for the first time in the journal "Proceedings of the National Academy of Sciences" (PNAS).

Hardly imaginable is the attraction that red blood cells exert on each other. A team of physicist Professor Gerhard Gompper from the Institute of Complex Systems at Forschungszentrum Jülich calculated a value of just three to seven Pico-Newton - trillionth Newton.

Virtual experiments

"So far, there are no ways to experimentally measure these attractions, " explains the expert in theoretical physics and simulation. "That's why we've recreated the properties of blood in the computer. So we could do virtual experiments that would not be possible in practice. This helps to better understand the physical relationships in blood. "Computer simulations could thus contribute to a better understanding of the symptoms of diseases or in the development of microfluidic systems, for example for diagnostic purposes.

Using their simulations, the researchers were able to investigate the relationship between the microscopic arrangement of the red blood cells and the properties of blood, such as the flow resistance, - the viscosity -. "In particular, attractive forces cause two or more blood cells to temporarily stick to each other instead of gliding past each other - which is equivalent to increased flow resistance, " explains Gompper.

Researchers use molecular dynamics

The researchers use so-called molecular dynamics, a recognized method of theoretical physics, in which interactions between molecules over a time course are simulated. Since the necessary computing power was enormous and would have taken many months on an average PC, the researchers expected high-performance computers, such as the Jülich supercomputer JUROPA. display

The basis of the calculations were two model systems. In a simpler model, the individual red blood cells were represented by a few spherical particles, which are connected by springs to a discus-shaped structure. Comparisons with data from experiments showed that even this comparatively simple model predicts the viscosity of blood very reliably.

For the simulation of blood flow through very narrow vessels, however, a detailed model was needed that also takes into account the cell membrane of the blood vessels, which is bendable and allows deformations. The detailed model also allowed investigations of properties of red blood cells, such as their deformability and just the forces of attraction among themselves.

Soon predictions for circulatory disorders?

We've calibrated our data with data from experiments, as far as they exist, and therefore know that our models work well, says Gompper. We therefore plan to investigate the changed properties that can be found in the blood of patients in the future. Diabetes, for example, reduces the deformability of red blood cells. As a result, the flow resistance of the blood increases and the blood circulation worsens. Here we can imagine that the routine investigation of the properties of individual red blood cells leads to diagnostic predictions for circulatory disturbances. (PNAS Early Edition; 2011; doi: 10.1073 / pnas.1101210108)

(Forschungszentrum J lich, 13.07.2011 - DLO)