Keeping Your Baby's Precious Cells in "Suspended Animation"
Being able to keep the important stem cells in cord blood and birth tissues alive and stored for a long period of time is the key to the utility of "banking" them for later use. This is achieved by freezing, or cryopreservation, of the cells; but how to effectively accomplish this is a bit more complicated than as if storing leftovers in the kitchen freezer.
If these precious cells were simply placed into freezing temperatures, they would almost all be destroyed due to massive and uncontrolled ice formation that can rupture the cells. It should be no surprise that quite a bit of the cell is made up of water. When subjected to freezing temperatures, water transitions to ice crystallization. This needs to be done in a controlled manner because if the rate is too fast there may be too much damaging ice formed inside the cells, but if the rate is too slow then the cells will be exposed too much to the salty environment left after ice forms from water around the cells. This balance is like a "Goldilocks Effect" (not too fast, not too slow).
Therefore, a foundation for preserving the cells is to control the formation of ice, and then to reduce the stresses that cells would encounter during the process of freezing and thawing. In order to effectively accomplish these goals following isolation of the stem cells, the cells are placed in a cryopreservation solution containing cryoprotectants, introduced to a controlled freezing process at a specific rate of cooling ("slow freeze"), stored at very low freezing temperatures (much colder than the leftovers in the kitchen freezer!), thawed quickly ("fast thaw"), and then appropriately applied to the patient.
The cryopreservation solutions used in stem cell therapies utilize cryoprotectant compounds within a liquid formulation. The cryoprotectants act to reduce cellular damage from ice crystal formation. The most common mechanism for this with therapeutic cells is to utilize a single cryoprotectant that permeates the cells, and promotes dehydration of the cells so there is less likelihood for formation of ice crystals inside the cells. In addition, newer cryopreservation solutions also use a mixture of salts and sugars to "buffer" the cells during this cold exposure (similar to putting a "coat" on the cells to protect them from the cold), as well as to incorporate multiple cryoprotectants, to enhance the protection of the cells.
Another important detail is the temperature that the cells are kept for long term storage. For reference, a standard kitchen refrigerator freezer is often in the range of -5°C to -10°C. Even though this is "frozen" to the naked eye, cellular activity is not effectively suppressed until stored below a point called the glass transition temperature, and cellular degradation will continue to occur if the storage temperature is not cold enough. Therefore, for long term biopreservation, cord blood banks store cells at temperatures of -130°C or colder.
Imagine, for a moment, all the stresses and variations the cells are subjected to when going from inside the mother's warm body, to being transported to the processing lab, chilled and then frozen at cold temperatures, thawed back to a warm temperature, and finally introduced into a patient. There is only a limited number of precious stem cells in cord blood and birth tissue, and they may not be needed for many years after childbirth. So the cryopreservation of these cells is a controlled and scientific process in order to keep those valuable cells alive in sufficient numbers, and with functional viability to allow for therapeutic benefit. Should those cells be needed one day down the road, the last thing you would want to deal with would be not having enough precious cells survive the cryopreservation process.