Cryopreservation is a scientific advancement that has allowed cells and tissues to last exponentially longer than without. Because of this longevity that cryopreservation provides we are able to preserve beneficial biological materials for future use. One of these materials that have become a staple for cryogenic-based companies is cord blood stem cells. But how exactly does this cord blood freezing process occur? This article will discuss the procedure of isolating, freezing, and thawing a cord blood sample for use in the future.The first step in the freezing process of stem cells is the isolation of the cells themselves from umbilical cord blood. Cord blood freezing starts when the umbilical cord blood is first treated with a buffer that allows the sample to be separated into distinct regions (Miltenyi) (Kanof). Once the buffer has been added the sample is then rapidly spun through a centrifuge. This causes the layers of cells to be separated based on gravity. Once the cells are distinctly layered, the top layer is removed, and the mononuclear layer (lymphocytes, monocytes, and thrombocytes) is then isolated into a new container (Miltenyi) (Kanof). This new mixture is then treated with buffer and centrifuged again, giving a mass of cells that will actually be frozen.
The freezing process is dependent on two aspects, the time it takes to freeze a sample and a cryoprotectant. A cryoprotectant is a chemical compound that, as the name suggests, protects the sample during the freezing process (Answer). The cryoprotectant does this by increasing the solute concentration inside the cells, and thusly removing water from inside the cell which would be damaging during the cooling process (Simione). The common cryoprotectant used for stem cells is DMSO (Dimethyl sulfoxide); this in combination of fetal bovine serum (for cell nourishment) is what will surround the cell during freezing. Once the cells have been treated the next step is the cooling process. The rate of cooling is very important because it affects the formation and size of ice crystals formed, which are harmful to the cells (Simione). For stem cells the recommended rate for cooling is generally around -1 degree per minute until the sample is -150 degrees. To achieve this constant rate of cooling, a special freezer is used that actually controls the drop in temperature to allow for consistent freezing. The sample is then transferred to a cryogenic tank until needed.If the stem cells ever need to be used they must be thawed for transplantation. The process is actually very simple compared to the rest of the procedure. Most cells require an almost rapid thawing to prevent damage to the cells (Simione). To do this, the sample is simply placed in a 37-degreewater bath and allowed to thaw. Once the sample is fully thawed, the sample is then transferred to a growth medium to allow for expansion and observation.Cryopreservation is on the forefront of biological sciences and is constantly being improved. It has given the scientific community the chance to hit the pause button and allowed for careful scrutiny. We have been given the opportunity for a family to have a child in the future, even though their lives may have taken turns for the worse. Although the process seems daunting, it is a necessary tool for modern medicine and can allow for further scientific achievements.
"Isolation of Mononuclear Cells from Human Cord Blood by Density Gradient Centrifugation." Print. (Miltenyi)
Kanof, Marjory, Philip Smith, and Heddy Zola. "Preperation of Human Mononuclear Cell Populations and Subpopulations." Web. 21 Jan. 2015. . (Kanof)
Simione, Frank. "Thermo Scientific Nalgene and Nunc Cryopreservation Guide." Web. 21 Jan. 2015. . (Simione)
"Answer." The Process of Cryopreservation. Web. 19 Jan. 2015. . (Answer)
THE CONTENT OF THIS ARTICLE DOES NOT PROVIDE MEDICAL ADVICE.It is intended for general informational purposes only and is not a substitute for professional medical advice or treatment. If you have a medical emergency or question, immediately call your doctor or dial 911 for assistance.
