Minimum Essential Medium Eagle (EMEM): A Widely Used Synthetic Cell Culture Medium
When it comes to cell culture, finding a suitable medium is crucial to ensure optimal growth and health of cells. One of the most widely used synthetic cell culture media is Minimum Essential Medium Eagle (MEM). Developed by Harry Eagle, this medium was first introduced in 1959 and has since become a popular choice for a variety of cell types grown in monolayers and attached cell lines.
What's in EMEM?
EMEM is a modified version of Eagle's minimum essential medium, containing Earle's Balanced Salt Solution, non-essential amino acids, two mM L-glutamine, one mM sodium pyruvate, and 1500 mg/L sodium bicarbonate. It's important to note that this reduced level of sodium bicarbonate (NaHCO3, 1.5 g/L) is intended for use in 5% CO2 in the air. To maintain its effectiveness, it's recommended to store the medium at two °C to 8°C in the dark when not in use.
What is EMEM used for?
Eagle's minimal essential medium (EMEM) is a cell culture medium that can maintain cells in tissue culture. The medium contains higher concentrations of amino acids, allowing for a more accurate approximation of the protein composition of cultured mammalian cells. EMEM may be used to cultivate various cells, including fibroblasts, human liver cancer cell line (HepG2) cells, and human fetal brain progenitor-derived astrocyte cells (PDA). It is typically used in the presence of fetal bovine serum (FBS), calf, or horse sera.
How is EMEM different from other cell culture media?
While EMEM and Dulbecco's modified Eagle's medium (DMEM) share some similarities, they also differ. Both media lack protein and contain the amino acids, salts, glucose, and vitamins required to provide a cell with energy and maintain it in tissue culture. However, the DMEM formulation is modified to contain up to four times more vitamins and amino acids and two to four times more glucose than EMEM. It's worth noting that EMEM is also different from the original MEM formulation. 
EMEM 2X contains:

Twice the amount of MEM.
Four times the vitamins and amino acids of the original MEM.
Earle's salts which allows for the culturing of an even wider variety of more nutritionally fastidious cells.

In conclusion, Minimum Essential Medium Eagle (EMEM) is a widely used synthetic cell culture medium that has been instrumental in the cultivation of various cell types. With its higher concentration of amino acids and accurate approximation of the protein composition of cultured mammalian cells, EMEM is a popular choice for maintaining cells in tissue culture. While it shares some similarities with other cell culture media, EMEM's unique formulation and properties make it a valuable addition to any cell culture laboratory.