Red blood cell transport in bounded shear flow: On the effects of cell viscoelastic properties

Red blood cells (RBCs) are able to undergo significant shape changes when they flow in the microcirculation thanks to their ability to withstand large deformations. In this context, particular attention should be dedicated to the role of RBC deformability and membrane viscosity on the RBC fluid dynamics at the microscale. Experimentally investigating the impact of the RBC viscoelastic properties is challenging due to the overlapping effects of multiple viscous dissipation sources, making high-fidelity cell -resolved simulations crucial. This work focuses on (i) developing a fluid-structure interaction framework to predict the RBC dynamics at the microscale and (ii) evaluating the impact of the cell viscoelastic properties such as deformability, viscosity contrast and membrane viscosity on the RBC transport in bounded shear flow. An incompressible Lattice Boltzmann method (LBM) is adopted to resolve the fluid dynamics inside and outside the RBCs, alongside with a tagging procedure to assign a viscosity contrast between the cytoplasm and the plasma. A finite -element model coupled with the Standard -Linear -Solid model describes the viscoelastic behavior of the RBC membrane. The interaction between the fluid and the RBCs is enforced by means of an immersed -boundary (IB) technique. Benchmark tests are performed to simulate the deformation of a purely elastic capsule, a viscoelastic capsule, and a viscoelastic RBC subjected to a bounded shear flow. A good agreement is found between the present results and literature data obtained with similar IB-LBM methods. The analysis of the impact of the cell viscoelasticity on the RBC dynamics highlights the importance of including the membrane viscosity and a physiological viscosity contrast in the RBC model, especially when investigating the RBC time -dependent behavior. Overall, our findings revealed that adding a viscous term in the RBC model significantly impacts the migration timescale but has a minor effect on the RBC final equilibrium position.