It came as something of a sensation when Sydney Ringer managed to keep frog hearts beating after they had been removed from the amphibians’ bodies in 1882. Using the saline solution bearing his name, the British doctor and pharmacologist ushered in the age of culture media. A success that immediately attracted imitators: Some solutions were mixed with glucose as a nutrient, for example, but the basic components always remained the same: inorganic salts. Since the salt concentration, pH value and osmotic pressure were modeled on physiological conditions, cells and tissue were able to survive in these balanced saline solutions even outside the body– though only for a few days at most.
Lymph helps nerves grow
The next breakthrough came a full 15 years later. Ross Granville Harrison (1870-1959) placed the nerve fibers of a tadpole in fresh lymphatic fluid that he had taken from a fully-grown frog. In this way, the American biologist was able to not only keep the neurons alive, he even managed to get them to grow for several weeks. This experiment is considered to mark the birth of animal cell cultures. Ross Harrison, who had also worked for several years in Bonn before this pioneering feat, was nominated for the Nobel Prize in Medicine or Physiology a total of 15 times, but always came away empty-handed.
This prize was awarded to Alexis Carrel in 1912 for his groundbreaking achievements in vascular surgery. The French doctor and biologist, born in 1873, dominated the field of cell cultures for many years with his “plasmatic medium,” as he called it. It was based on a saline solution that Carrel mixed with blood plasma from chickens and an extract from chicken embryos. By regularly replacing the growth medium, he was initially able to cultivate connective tissue cells from the hearts of chicken embryos, and then later cells from mammals, over a long period of time.
A great intellect – but a doubtful mentality
Carrel’s accomplishments as a scientist are beyond dispute. But as his principal work, “Man, The Unknown,” that was published in 1935 revealed, he was also a convinced racist who explicitly extolled the euthanasia ideology of the German Nazis and specifically argued that “the propagation of the defective, the mentally diseased, and the criminal” should be prevented through the use of “suitable gases.” Alexis Carrel died in Paris in 1944; a culture of embryonic chicken heart cells he started in 1912 allegedly outlived him by two years.
Harry Eagle and the staple diet of cells
His “plasmatic medium” remained the standard right up to the 1950’s and the mystery that Carrel left behind was only solved little by little: Which substances in blood plasma and embryo extract are needed by cells to grow in a laboratory? One of the first people to describe their nutritional needs more precisely was Harry Eagle (1905-1992). The New York-born doctor and pathologist discovered that a series of amino acids and vitamins are indispensable for a large number of cell lines – both animal and human. Based on these findings he developed “Eagle’s Minimal Essential Medium” at the National Institutes of Health at the end of the 1950’s. This medium contains glucose, six inorganic salts, 13 amino acids, eight water-soluble vitamins and dialyzed blood serum.
Harry Eagle laid the foundations for the in-vitro cultivation of living cells with his defined growth media. They are still in use today in modern cell culture technology. Some of them in a modified, improved form that are particularly suitable for certain types of cells – such as “Dulbecco‘s Modified Eagle Medium,” which was co-developed by the Italian-American cancer researcher and winner of the Nobel Prize in Medicine Renato Dulbecco.
The move towards tailor-made culture media
The first completely synthetic nutrient solution was made by Richard G. Ham in 1965 at the University of Colorado. However, “Ham’s F12” medium only worked with CHO cells, a cell line from the ovaries of Chinese hamsters. It proved very difficult to cultivate other types of cell with this solution. In the 1970’s, the development of serum-free, synthetic culture media then moved forward in leaps and bounds. Researchers gained an increasingly better understanding of which growth factors, hormones, vitamins, trace elements, and other substrates cells need to thrive outside their natural environment. And that needs may differ depending on the kind of cell.
Today, there is a wide variety of ready-to-use growth media for sale, each of them tailor-made for the type of cell that is currently of interest. Whether for the study of diseases, for medical diagnoses, to manufacture vaccines and serums, or in reproductive medicine – cell culture technology has long become indispensable in a number of fields. This would never have been possible without the evolution of growth media that all began with Sydney Ringer.