Abstract
Microvascular networks feature a complex topology with multiple bifurcating vessels. Nonuniform partitioning (phase separation) of red blood cells (RBCs) occurs at diverging bifurcations, leading to a heterogeneous RBC distribution that ultimately affects the oxygen delivery to living tissues. Our understanding of the mechanisms governing RBC heterogeneity is still limited, especially in large networks where the RBC dynamics can be nonintuitive. In this study, our quantitative data for phase separation were obtained in a complex in vitro network with symmetric bifurcations and 176 microchannels. Our experiments showed that the hematocrit is heterogeneously distributed and confirmed the classical result that the branch with a higher blood fraction received an even higher RBC fraction (classical partitioning). An inversion of this classical phase separation (reverse partitioning) was observed in the case of a skewed hematocrit profile in the parent vessels of bifurcations. In agreement with a recent computational study [P. Balogh and P. Bagchi, Phys. Fluids 30,051902 (2018)], a correlation between the RBC reverse partitioning and the skewness of the hematocrit profile due to sequential converging and diverging bifurcations was reported. A flow threshold below which no RBCs enter a branch was identified. These results highlight the importance of considering the RBC flow history and the local RBC distribution to correctly describe the RBC phase separation in complex networks.
Highlights
Living tissues rely on the supply of oxygen and nutrients as well as on the removal of carbon dioxide and other metabolites[21] to maintain a physiological state
Velocity measurements are validated against the Line Scan Method[27] (LSM) and the mass balance is verified at the bifurcations
We found that the red blood cells (RBCs) splitting at diverging bifurcations is not proportional to the blood flow fraction in the daughter branches, which agrees with the consensus in the literature that phase separation at diverging bifurcations is dominated by the Zweifach-Fung effect.[5,41,47,52,53]
Summary
Living tissues rely on the supply of oxygen and nutrients as well as on the removal of carbon dioxide and other metabolites[21] to maintain a physiological state. The microcirculation is the system where these mass exchange phenomena are happening. Microvascular networks feature a complex topology with highly interconnected capillaries bifurcating in an irregular fashion.[10,22] Blood flowing in the microcirculation cannot be treated as a homogeneous Newtonian fluid because it contains deformable red blood cells (RBCs), whose dimensions are comparable to the vessel diameter.[50]. The particulate nature of blood and phase separation effects must be considered for a correct interpretation of fluid dynamics at the microscale. In such microvascular networks, the dynamics of RBCs flowing through sequentially diverging and converging bifurcations plays an important role in the local perfusion
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