Red Blood Cell Positional History, Sphericity, and Network Architecture Influence Lingering and Partitioning.

The transport and distribution of red blood cells (RBCs) through microvascular networks is central to diverse applications in drug delivery, tissue engineering, and the study of pathological mechanisms. Recent findings highlight two critical phenomena: (i) a history-dependent partitioning effect, wherein the RBC partitioning at each bifurcation is influenced by the positional and configurational state inherited from previous bifurcations and (ii) RBC lingering at the bifurcation apex, which strongly affects downstream flow distribution. However, the interplay between network geometry, RBC sphericity (in spherocytosis disease), and these emergent behaviors remains insufficiently explored. Here, we perform two-dimensional Lattice Boltzmann simulations coupled with an immersed boundary model to systematically investigate RBC dynamics in both asymmetric and fully symmetric network designs. Our results show that RBC positional history grows progressively with each bifurcation, leading to increasing deviations from classical partitioning laws regardless of the network's geometric complexity. We further demonstrate that even spherical RBCs can experience substantial lingering due to cumulative apex interactions, challenging the notion that only elongated or pathologically deformed cells are prone to these effects. These findings clarify how RBC deformability and prior apex encounters affect microcirculatory flow.