A strain-based flow-induced hemolysis prediction model calibrated by in vitro erythrocyte deformation measurements.

Hemolysis is caused by fluid stresses in flows within hypodermic needles, blood pumps, artificial hearts, and other cardiovascular devices. Developers of cardiovascular devices may expend considerable time and effort in testing of prototypes, because there is currently insufficient understanding of how flow-induced cell damage occurs to accurately predict hemolysis. The objective of this project was to measure cell deformation in response to a range of flow conditions, and to develop a constitutive model correlating cell damage to fluid stresses. An experimental system was constructed to create Poiseuille flow under a microscope with velocities up to 4 m/s, Reynolds number to 200, and fluid stresses to 5000 dyn/cm(2). Pulsed laser illumination and a digital camera captured images of cells deformed by the flow. Equilibrium equations were developed to relate fluid stresses to cell membrane tension, and a viscoelastic membrane model was used to predict cell strain. Measurements of aspect ratio as a function of shear stress and duration of shear were used to calibrate the cell deformation model. Hemolysis prediction was incorporated with a threshold strain value for cell rupture. The new model provides an improved match to experimentally observed hemolytic stress thresholds, particularly at long exposure times, and may reduce the empiricism of hemolysis prediction.