High-quality basal media and supplements are crucial to successful and predictable experiments. Today there are many good and reliable sources of basal media and supplements.
However, there is a certain amount of variability in culture media, which comes primarily from the addition of serum or serum substitutes, which are either wholly or partially, animal derived.
Serum is a biological product; therefore variation exists from lot to lot. Finished FBS is typically produced in large batches of up to 3,000 liters originating from several thousand individual animals. This pooling method minimizes the variability of cell culture performance.
However, raw serum samples can vary in the age of animal at collection, animal diet, country of origin, and various other factors. With large lots, the likelihood of consistent cell culture performance increases. Additionally, many vendors now test lots for compatibility with ESC culture.
Serum substitutes and replacements, which are more defined than serum, may improve ESC experimentation by providing a more predictable culture medium and eliminating some of the variability found in serum products. But it is important to remember that currently available serum substitutes are biological materials derived from serum.
With this potential for variability in mind, thorough testing should be performed to determine long-term stability and pluripotency of an ESC line both when changing media or culture conditions.