Speaker
Description
Flow-induced red blood cell damage (hemolysis) occurs when flow forces induce excessive deformation or rupture of red blood cells (RBCs). While physiological flow conditions are generally well tolerated by RBCs, blood-handling medical devices can expose them to high stresses. Hemolysis is therefore a key factor in the design process of ventricular assist devices.
The numerical prediction of this phenomenon is based on computational fluid dynamics (CFD) simulations. Simple stress-based hemolysis models post-process the CFD results by reducing three-dimensional fluid stresses to representative scalar stresses. Flow vorticity, i.e., the antisymmetric part of the velocity gradient, is generally neglected in these models. More complex strain-based models resolve RBC deformation and orientation. This way, they can account for the viscoelastic behavior of the RBC membrane and take into account all flow components, including vorticity.
Due to the widespread popularity of stress-based models, vorticity is not commonly takien into account when modeling hemolysis. We systematically compare stress-based and strain-based models to investigate the influence of vorticity on RBCs. We find that vorticity affects cell orientation and deformation. We show a selection of test cases to illustrate the effect of vorticity on red blood cells. Moreover, we show how our findings help explain experimental observations on the significance of extensional stresses over shear stresses.
Overall, the results suggest that vorticity is an important factor in hemolysis modeling. Strain-based models can naturally account for such effects by modeling the cell’s response to the local flow field. Stress-based models, however, need to be extended to include vorticity. This also has implications for the design and interpretation of hemolysis experiments, which have historically focused on shear stresses.
