Based on the source and composition of culture media, its development has undergone three stages: the natural culture media stage, the synthetic culture media stage, and the serum-free culture media stage.
In the 1950s, in vitro cultures commonly relied directly on tissue clots, biological fluids, and tissue extracts such as plasma clots, serum, lymph fluid, and embryo extract, marking the natural culture media stage. Due to the inevitable issues of viral contamination and significant batch-to-batch variations associated with natural culture media, synthetic culture media was developed, primarily consisting of growth factors, nutrients, buffers, and antibiotics. The initial formula for synthetic culture media, MEM, was proposed by Eagle in 1959. Subsequently, various high-quality synthetic culture media formulations such as M199, DMEM, IMDM, and PRMI1640 emerged, and these classic culture media remain widely used in laboratories today.
Since some nutrients in natural culture media cannot be completely replaced by synthetic media, serum components are generally added to complete culture media. The addition of serum can be challenging at times, such as when controlling exogenous protein levels in the culture system or when needing to completely eliminate batch-to-batch variability in serum. Moreover, the high cost of serum has driven researchers to seek alternative solutions that achieve the same culture effects. Hence, serum-free culture media came into existence, and it has progressed to the stage of chemically defined media.
Of course, the most commonly used are still some classic synthetic media. According to their physical properties, they can be categorized into: liquid medium for bacterial growth, solid media, semi-solid medium, and dehydrated medium. Liquid medium for bacterial growth is the most common, offering the advantage of enabling aerated or shaking cultures due to their fluidity, which facilitates precise control over the solution temperature, nutrient concentration, and gas content. It requires minimal adherence capability from the cells during growth, allowing for rapid cell proliferation and being more economical and efficient for large-scale cell culture. As the most frequently used reagent in cell culture, liquid medium for bacterial growth plays a crucial role.
To meet the growth needs of cells, liquid medium for bacterial growth generally contains water, energy sources, amino acids, vitamins, inorganic salts, and pH indicators.
Water
Over 90% of liquid cell culture media is water. The quality of water directly affects the outcome of cell culture. Water for cell culture must be purified, meeting the standards for injection water outlined in the Chinese Pharmacopoeia or the standards for ultrapure water.
Energy Sources
Glucose is the primary energy source in liquid medium for bacterial growth, with some containing galactose, fructose, mannose, etc. Depending on glucose content, cells with high metabolic consumption, such as those in pathological states, often use high-glucose (4.5g/L) media, while low-glucose (1.0g/L) media are used during monoclonal cell fusion. Sodium pyruvate can be used as an alternative carbon source when glucose is insufficient, and some cell lines are dependent on sodium pyruvate.
Amino Acids
Amino acids are the building blocks for protein synthesis, and different cell types require different amino acids. Glutamine is a critical amino acid and an important energy source but is unstable in solution, with its metabolites potentially damaging sensitive cell lines.
Vitamins
Vitamins are involved in enzyme formation and are bioactive substances vital for maintaining cell growth, playing regulatory and controlling roles in cell metabolism.
Inorganic Salts
The primary role of inorganic salts is to maintain osmotic balance and regulate pH.
Buffer Systems
The main substance causing pH fluctuations in culture media during cell culture is CO2 produced by cell metabolism. Liquid medium for bacterial growth typically employs NaHCO3 or HEPES buffering systems to provide a stable pH environment for cell growth.
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