Buckling of red blood cell membrane in narrow capillaries induces excessive wall shear stress.

The deformation of red blood cells (RBCs) in Poiseuille flows of capillary vessels is fundamental for hemodynamics in cellular scale for various physiological or pathological scenarios. However, the mechanical criterion for membrane buckling and the impact of the asymmetric deformations of cells on the hemodynamics are currently unclear. In this study, a microfluidic system with narrow tubular channels was set up for experimental observations, and numerical simulations using the immersed boundary method were performed to illustrate the deformation of RBCs and their surrounding flow fields in detail. The dependence of the buckling on the capillary number (a dimensionless parameter measuring the ratio of viscous fluid force with elastic force of membrane) was discovered. Then we derived the criterion of buckling of cell membrane under local circumferential pressure by considering the buckling of an elastic ring with neglecting thickness. Results also show that the extra pressure drop and the wall shear stress associated with the appearance of membrane buckling increase nonlinearly. This work provides biomechanical fundamentals for mechanobiological studies of microvascular disease associated with the change of mechanical properties of RBCs.