Animal cell media and serum

A typical medium for animal cells contains vitamins, amino acids, glucose, inorganic salts, serum and hormones, and keeps the right pH and osmolality (concentration of dissolved particles). The choice depends on the cells and the goal: growth, specialisation, or making a product.

Natural media, such as plasma clots, tissue extracts and body fluids, suit many cells, but they vary and are hard to reproduce exactly. So most labs use synthetic media: a basal medium plus supplements. They come in several kinds:

• serum-containing and serum-free media;
• xeno-free media, using only human components;
• protein-free media;
• chemically defined salt solutions, such as PBS and HBSS (balanced salt solutions);
• complex media, such as EMEM, DMEM, RPMI-1640 and Ham's F-12.

Serum, most often fetal bovine serum, is the blood fluid left after clotting. It supplies:

• nutrients: amino acids, proteins, vitamins and lipids;
• hormones and growth factors;
• carrier proteins such as albumin and transferrin;
• adhesion factors, which help cells attach to the surface of the flask.

But serum has drawbacks: it may lack enough of the growth factors a particular cell needs; it may contain toxic or growth-inhibiting compounds, and carry viruses, fungi or mycoplasma; it makes it harder to purify a product; and it varies from batch to batch.

Penicillin and streptomycin are often added to keep down bacteria and fungi, though they are not needed for the cells' growth.