Red blood cells under microgravity

Dynamics of red blood cell aggregates under flow in microgravity.

The formation of red blood cell (RBC) aggregates has several origins: (i) a structural alteration (example: glycoproteins) on the surface of RBCs, (ii) the presence in excess of certain enzymes, such as amylase, ( iii) an excess of aggregating proteins (fibrinogen) in the blood plasma. Amylase is overproduced as a result of several diseases (such as pancreatitis). It has also been documented, based on blood tests of Russian cosmonauts, that amylase activity is amplified after a space mission. In order to study the effect of amylase on RBCs under flow we designed an in vitro experiment, in a microfluidic circuit, to analyze the flow of a RBC solution in the presence of amylase and aggregating agents (dextran, a molecule that plays the same role as fibrinogen) with a concentration of dextran in the physiological range. On the ground, when the amylase concentration is in a physiological range, we observe small aggregates, which form and dissociate during the flow. When the amylase concentration increases, mimicking the effect of space missions, or pathologies, the size of the aggregates and their stability increase considerably. However, and this is an essential point, the RBCs and aggregates sediment during the flow in the experiments in the lab, and this introduces serious artefacts in the analysis of the intrinsic effects responsible for the formation of aggregates. It is for this reason that we have recently carried out experiments in microgravity in order to overcome these artefact in order to deduce adequate behavior laws of blood aggregates. Our preliminary results validate the conclusions reached on the experiments performed in the lab. The microgravity experiments were carried out as part of the CNES "National Center for Space Studies" 63/VP167 campaign, the parabolic flights were carried out by the Novespace team.