Media is the liquid
that bathes the cells
. It contains all the nutrient
s needed for cell growth and is adjusted to appropriate pH
. It often looks like a delicious kool-aid
type drink, but smelling it will deter anyone sane from drinking it.
For optimum cell growth the media must be changed every 2 to 3 days, or extra media must be added at the same intervals. Addition is the prefered procedure since it doesn't cause the cells to slow or stop growth as a complete change can.
Media comes as a fine powder which is reconstituted with deionized water. It is manufactured to have low moisture content, be free flowing and readily soluble, and most importantly consistant from batch to batch.
Each cell line requires a specifc medium with the proper amounts of the following ingredients in order to survive:
Hank's Salts, a mixture of various salts
Earle's Salts, a mixture different than Hank's
Nonessential Amino Acids
Tryptose Phosphate Broth
Note: no media contain all these ingerdients, they are many of the possible ingredients.
In some cases media is ordered without certian ingredients because it is more cost effective to add them seperately. In particular, sodium barcarbonate, which changes the colour of the media I've used from yellow to red. Most cell lines also require the addition of FBS, Fetal Bovine Serum, at about 10 percent. This must be added seperately since it is sold as a frozen liquid.
Culture media must be sterilized for use in tissue culture. This is usually done by means of a vaccum filter. Media is generally stored in glass bottles, which have been sterilized by autoclave. The media cannot be autoclaved as that would change the dissolved gas content (and therefore the pH) as well as degrade some of the chemical components of the media. A check of the sterility should be preformed before using the media to culture cells, either by a manufactured test kit, or by simply placing some media in a flask and allowing it to incubate for 5 days. The flask should then be checked under a microscope for any growth.
Freezing media is manufactured by a few companies, or can be made with the regular medium by increasing the FBS content to 20 or more percent, and adding 10 percent DMSO, Dimethyl Sulphoxide. The DMSO does not need to be sterile because nothing ever grows in it, its toxic. This allows the cells to be frozen and thawed with mininal damage and loss. However, the DMSO is harmful to the cells, so when adding thawed cells in freezing media to a culture flask, it should be heavily diluted and changed soon after.