Cryopreservation

Cryopreservation, which derives from the Greek word cryo for “icy cold,” is a process whereby cells and sometimes whole tissues are preserved by cooling to very low subzero temperatures, often 77 K or minus 196 degrees C, the boiling point of liquid nitrogen. This is because at these very low temperatures any biological activity is effectively stopped, including those biochemical reactions that might lead to cell death. The problem is often that the act of freezing the cells at such low temperatures may seriously damage the cells. [Page 461]In addition, there can be problems with the high concentration of solutes, such as salt, in nonfrozen solution during freezing. Another problem encountered is too much extracellular ice, which can be fatal to some cells. It can cause mechanical damage through crushing and stresses associated with cellular dehydration. The discovery of the destructive forces of low temperatures has been put to use in cryosurgery.

The concept of cryopreservation was developed by Dr. James Lovelock, whose work showed that red blood cells were damaged during this freezing, although he felt that this was largely because of osmotic stress. Gradually, work by others has resulted in large numbers of cells and tissues being preserved. The cost of cryopreservation in terms of the energy used to freeze the products and then store them is significant, with the result that it tends to be a process for only a limited number of types of biological materials.

Cryopreservation is used for large numbers of blood products, especially special cells needed for transfusion, or stem cells. Similarly, tissue samples such as tumors and histological cross sections have been preserved. There has also been increased cryopreservation of semen, which can be used almost indefinitely after cryopreservation; human eggs (ococytes); and human embryos that contain two, four, or eight cells when they are frozen. Studies have shown that children born from such circumstances have no increased risk of birth defects.

In recent years there has even been an effort, known as cryonics, to preserve humans cryogenically. A number of people have arranged to have their head or brain or sometimes their whole body preserved at their death in the hope that future medical science and technology might advance sufficiently for people to be reborn.

A number of societies promote research in the area of cryopreservation. The main one is the Society of Cryobiology, which was founded in 1964 as the International Scientific Society for Low-temperature Biology and Medicine and which publishes the journal Cryobiology. In 1964 a Society of Low Temperature Biology was also founded in Britain.