Numerical analysis of shear rate in a rocking bioreactor and its impact on HL-60 lymphocytes

Abstract The aim of the study was to investigate the influence of hydrodynamic parameters on HL-60 lymphocyte cultures in a rocking disposable bioreactor. A 2D CFD-based model employing the Volume of Fluid (VOF) method was used to characterize the culture microenvironment, while a rotational rheometer was used to determine critical shear thresholds. The developed numerical model was validated against experimental mixing times, yielding an absolute mean percentage difference of 29.2%, demonstrating high predictive accuracy at very low and very high Reynolds numbers, though limitations were observed at medium Reynolds numbers. Results indicated that while averaged shear rates remained below 22.5 s⁻1, local maximum shear rates significantly exceeded the lethal threshold of 1500 s⁻1 for all studied rocking conditions, reaching over 30 000 s⁻1 at the highest parameters. Analysis of shear rate effects on HL-60 lymphocytes demonstrated that cell viability decreases at shear rates higher than 1000 s⁻1 due to cell membrane disruption, up to total disintegration of cells above 1500 s⁻1. The consistent exceeding of these lethal thresholds, particularly during intensified rocking, was shown to negatively impact cell growth and increase the release of intracellular enzymes. Consequently, the successful application of rocking disposable bioreactors for shear-sensitive cultures requires a strategic trade-off between mixing intensification and the mitigation of lethal local shear effects. The developed computational model provides a valuable framework for such optimization and subsequent bioprocess scale-up. Keypoints • 2D CFD VOF model well predicts hydrodynamics in rocking bioreactors. • Local maximum shear rates exceed 1500 s−1 as lethal threshold for HL-60 cells. • Intensification of cell culture requires balanced mixing and hydrodynamic stress.