Cryopreservation

Cryopreservation 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, the biochemical reactions that would lead to cell death are slowed or stopped. The cells being preserved, however, 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. The mechanism of cell damage due to intracellular ice formation is not well understood.

It is a commonly held misconception that the sharp edges of growing ice crystals cause physical damage to cells when they are freezing, and that this is a mechanism of freezing-related damage. This is incorrect, since crystals do not "move" during crystallisation, but rather add new molecules individually to the surface of the growing crystal. Thus, crystals grow around any solid object in their path.

One of the most important early workers on the theory of cryopreservation was James Lovelock of Gaia theory fame. Dr. Locelock'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

External links

• http://www.ivf.com/freezing