Cell culture began in the 19th-century when a physiologist, Sydney Ringer, developed a solution capable of maintaining a beating frog heart outside of the body. He was able to maintain the tissue under living conditions by submerging in an isotonic salt solution composed of sodium chloride, potassium chloride, calcium chloride and sodium bicarbonate. (1) A buffering system, usually phenol red, was also added to the culture media in order to monitor a pH at physiological ranges. In the years 1907 to 1910, specific methodology for cell culture was established by Ross Granville Harrison. He was the first to be able to observe neural growth. In his experimentation, he placed fragments of embryonic tissues from frog medullary cords on cover slips of glass slides and sealed them with clotted lymph. He indeed generated the first moist chamber. (2) Apart from the nutrition, animal cells also need specific culture conditions; they are kept in incubators in a controlled humidified gas mixture of 5% CO2 and 95% O2 under a physiological temperature of 37° C. The CO2 is essential to maintain the pH of media because without CO2 the medium becomes alkaline and compromises cellular survival and proliferation.
Cell culture techniques made significant advances in the 1940s and 1950s to support research in virology. As viruses require the components of infected cells to reproduce themselves, large scale manufacturing of viral material in safe conditions necessitates co-culture with animal cells. For instance, the vaccine for Polio was produced with the aide of co-cultured fetal cells. Harry Eagle, an American pathologist, defined the minimal requirement in 1955 for the Hela cell line (isolated from a human uterus Carcinoma at Johns Hopkins Hospital) and mouse fibroblasts, laying down the fundamental principles of mammalian culture. Eagle proved that 27 elements were essential for the growth of mammalian culture, and his medium Eagle's minimal essential medium (Eagle's MEM) contains various amino acids, glucose, vitamins, isotonic salt solutions and an whole animal or human serum. (3) All of the elements were defined as the base medium without the serum component. Dulbecco formulated a modified version of the Eagle's MEM, Dulbecco's MEM (DMEM) around the same time period, with 4 times more vitamins as reported in Table 1. Historically cell culture has been done with the addition of serum to the culture medium to mimic the physiological condition of the body. The source of the serums can differ; it can be human serum, horse serum or cattle serum among the most common.
Serum provides the cells with nutrients, attachment factors, growth factors and hormones, binding and transport proteins, spreading factors, fatty acids, lipids and protease-inhibitors. All of these factors are essential for proliferation and differentiation of cells in culture systems.