The spleen is the largest organ in the lymphatic system and contains special tissue that filters the blood, getting rid of old or damaged red blood cells (RBCs). While RBCs have a disk diameter close to 10 microns, they must squeeze through the slit less than a micron wide to pass through the spleen’s filtration system.
A new article reports on a computational study that investigates how RBCs manage to squeeze through a submicron slit. The authors show that the formulated boundary integral method can successfully predict the dynamics of this process. This numerical method can be applied to a wide range of biological applications, including lab-on-chip technologies, microfluidic devices, drug delivery and cell extravasation.
For the fluids surrounding the RBC, they derived the boundary integral equations of a cell immersed in a confined fluid domain with prescribed inlet and outlet pressures, which sets their simulations apart from previous studies that used a prescribed velocity or flow rate. For the solid structure of the RBC, the authors employed a multiscale approach to the cell membrane that included three models at different length scales.
Simulations of an RBC squeezing through a submicron slit matched up well when compared with a real-world experiment involving an RBC squeezing through a submicron slit in a microfluidic device.
Lastly, the authors investigated the effects of pressure drop, volume-to-surface-area ratio, internal viscosity, and membrane stiffness of RBC deformation and internal stress. The findings showed that cytoskeletal proteins of RBCs could be stretched by more than 2.5 times under high hydrodynamic pressure. The bilayer tension could be large enough to open the mechanosensitive channels and further decrease the cell volume to allow it to pass through the slit.
Source: “Boundary integral simulations of a red blood cell squeezing through a submicron slit under prescribed inlet and outlet pressures,” by Huijie Lu and Zhangli Peng, Physics of Fluids (2019). The article can be accessed at https://doi.org/10.1063/1.5081057.
