Scaling Up and Scaling Down for Cell Culture Bioreactors

This chapter discusses the scaling up of a bioreactor based on geometrical similarity. The stirred tank bioreactor is the standard vessel for growing mammalian cells in industrial processes. Impellers can generally be classified into two types according to the flow pattern they generate: axial flow and radial flow. The purpose of agitation is to provide a homogenous chemical environment. Spatial heterogeneity of nutrients may subject cells to an oscillating environment as they traverse the reactor, leading to inferior growth or production performance. Cells in a stirred bioreactor may encounter shear stress caused by fluid flow, or be subjected to direct impact by moving mechanical parts such as the impeller. The design objective in scaling up a process is to produce product in quantities proportional to the scale. To meet that goal, all nutrients are supplied proportionally to the scale. In scale translation, the relationship of geometry-related physical parameters cannot all be kept constant.