Biomedical Engineering Reference
In-Depth Information
fermentation, air (sterilized by fi ltration) is sparged into the tank to supply oxygen, and the fermenter
is also operated at a temperature appropriate to optimal cell growth (usually between 25 and 37
C,
depending upon the producer cell type). In order to maintain this temperature, cooling rather than
heating is required in some cases. Large-scale fermentations, in which cells grow rapidly and to a
high cell density, can generate considerable heat due to (a) microbial metabolism and (b) mechani-
cal activity, e.g. stirring. Cooling is achieved by passing the coolant (cold water or glycol) through a
circulating system associated with the vessel jacket or sometimes via internal vessel coils.
5.3.3 Mammalian cell culture systems
Mammalian cell culture is more technically complex and more expensive than microbial cell
fermentation. Therefore, it is usually only used in the manufacture of therapeutic proteins that
show extensive and essential post-translational modifi cations. In practice, this usually refers to
glycosylation, and the use of animal cell culture would be appropriate where the carbohydrate
content and pattern are essential to the protein's biological activity, its stability or serum half-life.
Therapeutic proteins falling into this category include EPO (Chapter 10), the gonadotrophins
(Chapter 11), some cytokines (Chapters 8-10) and intact monoclonal antibodies (Chapter 13).
The culture of animal cells differs from that of microbial cells in several generalized respects,
which include:
•
they require more complex media;
•
extended duration of fermentation due to slow growth of animal cells;
•
they are more fragile than microbial cells due to the absence of an outer cell wall.
Basic animal cell culture media, such as Dulbecco's modifi ed Eagle's medium, generally contain:
•
most
L
-amino acids;
•
many/most vitamins;
•
salts (e.g. NaCl, KCl, CaCl
2
);
•
carbon source (often glucose);
•
antibiotics (e.g. penicillin or streptomycin);
•
supplemental serum;
•
buffering agent (often CO
2
based).
Antibiotics are required to prevent microbial growth consequent to accidental microbial
contamination. Supplemental serum (often bovine or foetal calf serum, or synthetic serum
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