Scale-up of embryonic stem cell aggregate stirred suspension bioreactor culture enabled by computational fluid dynamics modeling

The use of stirred suspension bioreactors as tools in large-scale stem cell expansion is becoming increasingly popular. A change in bioreactor scale results in altered hydrodynamic properties which greatly affect the cell product, particularly if the cells grow as aggregates. Computational fluid dynamic (CFD) modeling is a powerful tool that can be used in understanding the hydrodynamic properties within bioreactors, and the effect of these properties on aggregate formation and size. Currently, there is no standard protocol for predicting agitation rate to maintain aggregate size when moving from one reactor to the next. This study evaluates the use of seven different scale-up parameters commonly used to predict agitation rate in scale-up. For experimental testing, murine embryonic stem cells (ESCs) were grown as aggregates in 10-mL and 100-mL stirred suspension bioreactors. We showed that depending on which criteria was used for scale-up, the corresponding agitation rates differ greatly, causing significant differences in the cell growth. We determined that if the volume average energy dissipation rate (calculated through CFD modeling) or maximum shear stress were kept constant, aggregate sizes could be maintained through scale-up. Using these methods, we can scale-up stem cell growth efficiently without extensive testing of bioreactor agitation rates.