Unbaffled, Stirred Bioreactors for Animal Cell Cultivation

One of the main features of animal cell bioreactors is that the cultured cells lack a strong membrane and are therefore more prone to shear damage. It is widely accepted that animal cell damage in aerated bioreactors is mainly related to burst bubbles at the air–liquid interface. A viable alternative to sparged bioreactors, aimed at minimizing cell damage, may be represented by uncovered, unbaffled, stirred tanks, which are able to provide sufficient mass transfer through the deep free surface vortex that takes place under agitation. As a consequence the need for bubble formation and subsequent bursting accompanied by cell damage is conveniently avoided. In this chapter, mass transfer performance and hydrodynamic features (e.g., free surface shape, mixing time, power consumption) of this kind of bioreactor are described. The effects of changing liquid viscosity, impeller geometry, and reactor aspect ratio are also discussed.