In vitro characterization and numerical simulations of red blood cell transmigration through splenic inter-endothelial slits

During their circulation through the spleen, red blood cells (RBCs) are forced to squeeze through gaps between endothelial cells that are ~8 times narrower than its diameter. The ensuing squeezing motion causes large RBC deformations that remove old and diseased cells from the circulation. There is limited data about the deformation and stress experienced by RBCs. To study the mechanics of RBC splenic filtration, we designed
and characterized a family of microfluidic devices where a suspension of human RBCs flows through an array of channels of controlled length (L), width (W) and height (H). We varied these geometrical parameters (0.75<W<3, 4.5<H<10 and 1<L<5 um) and imaged the time-evolving RBC shape while crossing each channel, as well as the flow field through the channel by μ-PIV. We also investigated this process computationally by coupling a multiscale model of the RBC membrane with a boundary integral formulation of the fluids. The computationally flow field and cell deformation are consistent with experiments. In wider channels RBCs reorient into the direction of less constrain, whereas in narrower channels, cells fold (U shape) experimenting large deformations. We examined computationally the mechanics of folded cell shapes under different flow rates and slit geometries.