Numerical study of blood microcirculation and its interactions with the endothelium

Abstract : This thesis is devoted to the study of the interactions between red blood cells (RBCs) and the endothelium, the monolayer of cells lining blood vessels. The endothelium and RBCs have been shown to be active participants in various processes in the vascular system, and their interactions trigger biochemical signalling by mechanical (wall shear stress) and chemical (signalling molecules) means. We first investigate the role of RBCs, including pathological conditions, in creating time- and space-varying shear stress on the endothelium. Shear stress has been shown to be a critical element in biochemical signalling from the endothelium. In addition, as it has been shown that the endothelium is undulating due to the individual endothelial cells comprising it, we take this into account in our model of the geometry of the vessel wall. We find that this undulation affects the dynamics of the RBCs in the flow and the wall shear stress. We briefly explore how the deformability of a single RBC affects its trajectory in undulating channels, inspired by the idea behind deterministic lateral displacement devices (DLDs) which exploit the differing trajectories of particles based upon their sizes to separate them in flow. We also investigate the effect of suspensions of RBCs in undulating channels on rheological properties and wall shear stress. Finally, we address the chemical interactions by building a numerical model with the lattice Boltzmann-immersed boundary method (LB-IBM) to solve advection-diffusion of solute released from moving, deformable particles. Oxygen and adenosine triphosphate (ATP) are both released by RBCs and are advected and diffused in the flow and uptaken by the endothelium and serve as critical signalling factors in inflammation and vasodilation. We find that the morphology of RBCs will affect the residence time and dilution of the chemical species upon contact with the wall. Together, these elements lead us towards the development of a model capable of simulating vital processes in the vascular system which result from local interactions of individual components.
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Brenna Hogan. Numerical study of blood microcirculation and its interactions with the endothelium. Biological Physics [physics.bio-ph]. Université Paris-Saclay, 2019. English. ⟨NNT : 2019SACLX004⟩. ⟨tel-02167871⟩

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