Blood Damage Models and Their Role in Cardiac Assist Device Development

Modeling and computational analysis play an increasingly-important role in bioengineering, particularly in the design of implantable ventricular assist devices (VAD) and other blood-handling devices. Numerical simulation of blood flow and associated physiological phenomena has the potential to shorten the design cycle and give the designers important insights into causes of blood damage and suboptimal performance. The microstructure of the blood as the flowing medium affects the outcome of the analyses to a varying degree, depending on the task at hand. A set of modeling techniques is presented which are based on stabilized space-time finite element formulation of the Navier-Stokes equations, with a shear-slip mesh update used to accommodate the movement of the VAD impeller with respect to a non-axisymmetric housing. Specific issues affecting shape optimization in this setting, such as parametrization of complex 3D surfaces, mesh deformation, and sensitivity to constitutive model selection, will be discussed. In order to obtain quantitative hemolysis prediction, cumulative tensor-based measures of strain experienced by individual blood cells must be developed; red blood cells under shear can be modeled as deforming droplets, and their deformation tracked along pathlines of the computed flow field. Another aspect of blood pump performance is related to platelet aggregation and thrombus formation. A three-species model for platelet aggregation is being developed based on a set of physiological experiments in collaboration with the Aachen University Clinic.