Reactor Engineering in Large Scale Animal Cell Culture

Abstract

This article mainly addresses the issues associated with the engineering of large-scale free suspension culture in agitated bioreactors >10,000 L because they have become the system of choice industrially. It is particularly concerned with problems that become increasingly important as the scale increases. However, very few papers have been written that are actually based on such large-scale studies and the few that do rarely address any of the issues quantitatively. Hence, it is necessary very often to extrapolate from small-scale work and this review tries to pull the two types of study together. It is shown that 'shear sensitivity' due to agitation and bursting bubbles is no longer considered a major problem. Homogeneity becomes increasingly important with respect to pH and nutrients at the largest scale and sub-surface feeding is recommended despite 'cleaning in place' concerns. There are still major questions with cell retention/recycle systems at these scales, either because of fouling, of capacity or of potential and different 'shear sensitivity' questions. Fed-batch operation gives rise to cell densities that have led to the use of oxygen and enriched air to meet oxygen demands. This strategy, in turn, gives rise to a CO 2 evolution rate that impacts on pH control, pCO 2 and osmolality. These interactions are difficult to resolve but if higher sparge and agitation intensities could be used to achieve the necessary oxygen transfer, the problem would largely disappear. Thus, the perception of 'shear sensitivity' is still impacting on the development of animal cell culture at the commercial scale. Microcarrier culture is also briefly addressed. Finally, some recommendations for bioreactor configuration and operating strategy are given.

Studies supporting the use of mechanical mixing in large scale beer fermentations

“…Similar insensitivities to mechanical agitation under aerobic conditions using these experimental and analytical tools have recently been shown for E. coli (Hewitt et al 1998) and Corynebacterium glutamicum (Chamsartra et al 2005). Even animal cells, which do not have a cell wall, are now recognized as being more robust than it was first thought and many such cell lines have been shown to be able to be agitated at T  values up to 0.25 W/kg without a reduction in cell viability or productivity (Nienow 2006). positioned throughout the fermenter.…”

“…However, even animal cells, which were initially thought to be very sensitive to such forces because of the lack of a cell wall (Cherry & Papoutsakis, 1986) have been shown to tolerate relatively high mechanical stresses due to turbulent flow in a stirred bioreactor with mean specific energy dissipation rates, T  up to 0.25 W/kg (Nienow, 2006). On the other hand, because the fluid mechanical stresses associated with bubbles bursting at the surface of the media have local specific energy dissipation rates, T  (W/kg) two to three orders of magnitude higher than those found under typical agitation conditions (Boulton-Stone & Blake 1993), the stresses arising can damage such cells.…”

“…On the other hand, because the fluid mechanical stresses associated with bubbles bursting at the surface of the media have local specific energy dissipation rates, T  (W/kg) two to three orders of magnitude higher than those found under typical agitation conditions (Boulton-Stone & Blake 1993), the stresses arising can damage such cells. However, the damage can be essentially eliminated by the use of the surfactant, Pluronic F68, which prevents such cells attaching to bubbles so that when they burst, the cells are not in the vicinity of the very localised and intense stresses produced (Nienow, 2006).…”

Axial impeller selection for anchorage dependent animal cell culture in stirred bioreactors: Methodology based on the impeller comparison at just-suspended speed of rotation

“…Studies have shown that the only significant effect on the growth or viability of the cells comes from bubble bursting. But, these damages may be strongly reduced by adding a surfactant such as Pluronic F-68, for instance ( Nienow, 2006). The shear rate due to the liquid phase velocity field also takes several forms.…”

CFD Prediction of Heterogeneities in the Scale up of Liquid-Liquid Dispersions

“…Noteworthy, similar results were found by Gelves [10] who analyzed CFD simulations of a Rushton turbine. The different liquid velocity contours are also checked by the analysis of Kolmogorov length scale [15]:…”