Cryopreservation
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Cryopreservation, also cryogenically freeze, is a process where cells or whole tissues are preserved by cooling to low sub-zero temperatures, such as (typically) -80°C or -196°C (the boiling point of liquid nitrogen). At these low temperatures, any biological activity, including the biochemical reactions that would lead to cell death is effectively stopped. However, the cells being preserved are often damaged during the approach to low temperatures or warming to room temperature.
Two phenomena which cause damage to cells during cryopreservation are solution effects and intracellular ice formation. Solution effects are caused by concentration of solutes in non-frozen solution during freezing as solutes are excluded from the crystal structure of the ice. The mechanism of cell damage due to intracellular ice formation is not well understood.
A process that provides the benefits of cryopreservation without the damage due to ice formation or the need of toxic ice formation inhibitors such as DMSO is vitrification. This can be facillitated only by an extremely rapid drop in temperature preventing ice crystal formation and instead inducing water to form into a gel-like substance.
One of the most important early workers on the theory of cryopreservation was James Lovelock of Gaia theory fame. Dr. Lovelock's work suggested that damage to red blood cells during freezing was due to osmotic stresses.
Water bears (or tardigrada), microscopic multicellular organisms, can survive freezing at low temperatures by replacing most of their internal water with the sugar trehalose.
Usually, this technique is used for biological materials. Common examples include:
- Semen (which can be used successfully almost indefinitely after freezing)
- Tissue samples like tumors and histological cross sections