Mammalian cells are fragile and harder to grow than other cell types (such as yeast or bacteria), but their large-scale culturing is an economic boon because it allows for the production of proteins that are otherwise difficult/expensive/unethical to extract from living organisms.

There are two basic ways of culturing animal cells:

• The cells are immobilized on a substrate and then perfused with culture medium;
• The cells are in a free suspension which is very gently mixed and aerated.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.