The size, shape and structure of these aggregates, which determine blood rheology, are governed by a balance between hydrodynamic forces and aggregation forces that may significantly vary in conditions affecting blood composition and properties such as long-term space flight. In order to progress in the understanding of the mechanisms of RBC aggregation in flow and the modeling of blood rheology, and following a successful first set of parabolic flight experiments , we propose an interdisciplinary project to investigate these phenomena in a future sounding rocket experiment. The general objective is a characterization by advanced optical techniques of the morphology and size distribution of blood cell aggregates in flow as well as their dynamic evolution over timescales that require to suppress sedimentation for quantitative measurements. Measurements at moderate shear rates will allow to propose kinetic equations for the aggregation-disaggregation rates of RBCs in shear flow and improve rheological models of blood. At low shear rates, we will characterize the gel-like fractal structure of RBC aggregate networks, possibly coupled to rheological measurements. This will shed light on the structure-rheology relationship in blood, its yield stress and the influence of biological and environmental parameters. To further investigate the consequences of aggregation on the promotion of thrombus formation and ways to mitigate it, we will investigate the effects of nanoparticles and nanomaterials well-known for their modulation on blood coagulation kinetics. This will help develop targeted countermeasures to prevent cardiovascular dysfunction in space as well as on Earth.
