cryobiology (redirected from cryobiologist)

cryobiology [¦krī·ō·bī′äl·ə·jē]

(biology)

The use of low-temperature environments in the study of living plants and animals.

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Cryobiology

The use of low-temperature environments in the study of living plants and animals. The principal effects of cold on living tissue are destruction of life and preservation of life at a reduced level of activity. Both of these effects are demonstrated in nature. Death by freezing is a relatively common occurrence in severe winter storms. Among cold-blooded animals winter weather usually results in a comalike sleep that may last for a considerable length of time.

In cryobiological applications much lower temperatures are used than are present in natural environments. The extreme cold of liquid nitrogen (boiling at -320^°F or -196^°C) can cause living tissue to be destroyed in a matter of seconds or to be preserved for years and possibly for centuries with essentially no detectable biochemical activity. The result achieved when heat is withdrawn from living tissue depends on processes occurring in the individual cells. Basic knowledge of the causes of cell death, especially during the process of freezing, and the discovery of methods which circumvent these causes have led to practical applications both for long-term storage of living cells or tissue (cryopreservation) and for calculated and selective destruction of tissue (cryosurgery).

The biochemical constituents of a cell are either dissolved or suspended in water. During the physical process of freezing, water tends to crystallize in pure form, while the dissolved or suspended materials concentrate in the remaining liquid. In the living cell, this process is quite destructive. In a relatively slow freezing process ice first begins to form in the fluid surrounding the cells, and the concentration of dissolved materials in the remaining liquid increases. A concentration gradient is established across the cell wall, and water moves out of the cell in response to the osmotic force. As freezing continues, the cell becomes quite dehydrated. Salts may concentrate to extremely high levels. In a similar manner the acid-base ratio of the solution may be altered during the concentration process. Dehydration can affect the gross organization of the cell and also the molecular relationships, some of which depend on the presence of water at particular sites. Cellular collapse resulting from loss of water may bring in contact intracellular components normally separated to prevent destructive interaction. Finally, as the ice crystals grow in size, the cell walls may be ruptured by the ice crystals themselves or by the high concentration gradients which are imposed upon them.

By speeding the freezing process to the point that temperature drop is measured in degrees per second, some of these destructive events can be modified. However, most of the destructive processes will prevail. To prevent dehydration, steps must be taken to stop the separation of water in the form of pure ice so that all of the cell fluids can solidify together. The chief tools used to accomplish this are agents that lower the freezing point of the water. Glycerol, a polyalcohol which is compatible with other biochemical materials in living cells, is frequently used in cell preservation. Besides the antifreeze additive, refrigeration procedures are designed to control the rate of decline in temperature to the freezing point, through the liquid-solid transition, and below, to very low temperatures.

Cryopreservation

The earliest commercial application of cryopreservation was in the storage of animal sperm cells for use in artificial insemination. The microorganisms used in cheese production can be frozen, stored, and transported without loss of lactic acid–producing activity. Pollen from various plants can be frozen for storage and transport, facilitating plant-breeding experiments. Among the most valuable applications of cryopreservation is the storage of whole blood or separated blood cells.

Cryosurgery

Cellular destruction from freezing can be used to destroy tissue as a surgical procedure. One of the significant advantages of cryosurgery is that the apparatus can be employed to cool the tissue to the extent that the normal or the aberrant function is suppressed; yet at this stage the procedure can be reversed without permanent effect. When the surgeon is completely satisfied that he or she has located the exact spot to destroy, the temperature can be lowered enough to produce irreversible destruction. This procedure is of particular assistance in neurosurgery.

A second major advantage of cryosurgery is that the advancing front of reduced temperatures tends to cause the removal of blood and the constriction of blood vessels in the affected area. This means that little or no bleeding results from cryosurgical procedures.

A third major advantage of cryosurgery is that cryosurgery equipment currently employs a freezing apparatus that can be placed in contact with area to be destroyed with a minimum incision to expose the affected area.