CHAPTER FIFTEEN
LETHAL EFFECTS OF BUBBLES IN
ANIMAL-CELL CULTURE
DIRK E.MARTENS, MICHEL F.MULLER, CORNELIS D.DE
GOOIJER AND JOHANNES TRAMPER
Food and Bioprocess Engineering Group, Wageningen University, P.O.
Box 8129, 6700 EV Wageningen, The NetherlandsABSTRACT
One of the main problems in the scale-up of animal-cell cultures is supply
of oxygen and removal of carbon dioxide. It has long been known that
sparging causes excessive cell death due to the fragility of animal cells.
There is convincing evidence that this cell death occurs at bubble rupture
in the rapid retracting rim of the breaking bubble film and during the
subsequent collapse of the bubble cavity. Although unlikely, cell death
may also occur at the sparger during bubble formation either due to
contact of the cell with a rapid expanding bubble surface or due to the
local liquid flows. Also the subsequent rise of the bubble to the surface is
very likely not to cause cell death. However, during bubble formation and
rise cells may attach to the bubble and be transported to the surface where
they are killed. The number of cells killed per bubble increases with
bubble diameter for bubble diameters in the range from 0.5 mm to 6 mm.
Cell death may be prevented through the addition of certain protective
additives like Pluronics and Methocels. These additives protect the cells
most probably through reducing the severity of the bubble burst and
through strengthening the cell as a consequence of adsorption to the cell
membrane. In addition, some of these compounds prevent adsorption of
cells to the bubble surface and thus prevent the cells from being in the
danger zone. Apart from adding these additives, cell death may be
minimised by optimising the amount of oxygen transferred per bubble,
through increasing the height of the reactor.
Keywords: Animal cell, bubble, cell death, shear, PluronicINTRODUCTION
At present animal-cell culture is used for the production of a large number of
pharmaceutical proteins. With over 1200 proteins in clinical trials in 1998 this number is
expected to increase in the coming years. As a consequence there will be an increasing
demand for medium-and large-scale production facilities. For medium-(10 to 1000 litre)