Elongation deformation of a red blood cell under shear flow as stretch testing

The elongation of a tank-treading red blood cell (RBC) under shear flow was numerically simulated to understand its mechanical characteristics. The boundary element method was used to couple the viscoelastic deformation of the cell membrane and viscous flow of the surrounding fluids. Accordingly, it was found that elongation deformation and inclination angle, which depend on the cell membrane's viscoelasticity, inner viscosity, and swelling ratio, were related to the fluid traction difference between the suspending and RBC inner fluids. When the viscosity of an RBC is compatible with the suspending fluid, the elongation index responding fluid shear stress is similar to the responding external loads in the optical tweezers stretch, with different elongation mechanics. By identifying the viscoelasticity of the cell membrane to reproduce published experimental data, the strain hardening elasticity of the cell membrane was identified by modifying the model developed by Skalak et al. (1973); the exponential form of Fung (1973) successfully expressed the stronger strain hardening behavior for the latter deformation regime. These results indicate the applicability of the shear flow experiments as a stretch testing method to measure the viscoelasticity of the cell membrane.