Parameters for the microscopic ESL model.

The geometry of the blood vessel wall plays a regulatory role on the motion of red blood cells (RBCs). The overall topography of the vessel wall depends on many features, among which the endothelial lining of the endothelial surface layer (ESL) is an important one. The endothelial lining of vessel walls presents a large surface area for exchanging materials between blood and tissues. The ESL plays a critical role in regulating vascular permeability, hindering leukocyte adhesion as well as inhibiting coagulation during inflammation. Changes in the ESL structure are believed to cause vascular hyperpermeability and entrap immune cells during sepsis, which could significantly alter the vessel wall geometry and disturb interactions between RBCs and the vessel wall, including the wall-induced migration of RBCs and the thickening of a cell-free layer. To investigate the influence of the vessel wall geometry particularly changed by the ESL under various pathological conditions, such as sepsis, on the motion of RBCs, we developed two models to represent the ESL using the immersed boundary method in two dimensions. In particular, we used simulations to study how the lift force and drag force on a RBC near the vessel wall vary with different wall thickness, spatial variation, and permeability associated with changes in the vessel wall geometry. We find that the spatial variation of the wall has a significant effect on the wall-induced migration of the RBC for a high permeability, and that the wall-induced migration is significantly inhibited as the vessel diameter is increased.血管壁的几何形态对红细胞（red blood cells, RBCs）的运动具有调控作用。血管壁的整体形貌受多种因素影响，其中内皮表面层（endothelial surface layer, ESL）的内皮衬层是关键因素之一。血管壁的内皮衬层拥有巨大的表面积，可实现血液与组织间的物质交换。内皮表面层在调控血管通透性、阻碍白细胞黏附以及抑制炎症过程中的凝血反应方面发挥着关键作用。目前认为，内皮表面层的结构改变会在脓毒症期间引发血管高通透性并困住免疫细胞，这可显著改变血管壁的几何形态，并干扰红细胞与血管壁之间的相互作用，包括壁诱导的红细胞迁移以及无细胞层的增厚。为探究在脓毒症等多种病理条件下，因内皮表面层改变而发生变化的血管壁几何形态对红细胞运动的影响，我们采用二维浸没边界法（immersed boundary method）构建了两种表征内皮表面层的模型。具体而言，我们通过模拟研究了血管壁附近红细胞所受的升力与阻力，如何随与血管壁几何形态改变相关的壁厚度、空间变异度以及通透性发生变化。研究发现，当通透性较高时，血管壁的空间变异度对红细胞的壁诱导迁移具有显著影响；且随着血管直径增大，壁诱导迁移会受到显著抑制。