Cryobiology is the study of the effects of very low temperatures on living things. Cryobiology can be used to preserve, store, or destroy living cells. At very low temperatures, cellular metabolism (all the chemical reactions that drive the activities of cells) essentially stops. Freezing technology is used for food preservation, blood storage at hospitals and blood banks, sperm and egg storage, preservation of some transplant tissues, and certain delicate surgeries. Cryopreservation, the freezing and eventual thawing of living material, is the most advanced use of this technology.
Ice has been used to slow the decay of food for centuries, but the widespread industrial use of freezing has occurred only in about the last 100 years with advances in refrigeration and cryotechnology. By the 1940s, red blood cells were being frozen to provide blood supplies as needed to the wounded during World War II (1939–45). Not long afterward, farmers began freezing the sperm of bulls in order to impregnate cows at distant locations.
The cryopreservation of single cells or small clumps of cells has been carried out successfully. However, preservation of whole live organs by freezing is more difficult and—as of the beginning of the twenty-first century—have largely failed.
Cryopreservation involves keeping cells at extremely low temperatures until they are needed. Careful steps must be taken to insure that the frozen cells will survive and be in good condition when they are thawed. It is important that cells be healthy prior to freezing. Cryopreservation places stress on cells that can cause even some healthy ones to perish during the freezing and thawing process.
The most successful medical applications of cryopreservation are in blood storage and the field of fertility. Blood banks can freeze rare and individual blood types for up to 10 years. Patients who have leukemia (a type of cancer) and must undergo radiation treatments can have their sperm and bone marrow cells, which are radiation sensitive, frozen and stored for later use. Some men undergoing a vasectomy (a sterilization procedure) store sperm so that they have the option of fathering a child at a later date. In addition, fertilized eggs have been successfully frozen and thawed for placement into the female's uterus, or womb.
Medical scientists can also use freezing technology during surgical procedures to improve a patient's prognosis (the outcome of the surgery). In transplant surgery, eye or skin tissue to be transplanted is sometimes frozen before use. Cryosurgery is the freezing of unwanted tissue, such as precancerous lesions or warts, in order to destroy it. A major advantage of cryosurgery is that it produces less scarring than surgery in which the tissue is removed by cutting. Cold temperatures are also sometimes used to cool patients before an operation. When a patient's brain and heart are cooled, they need less oxygen, thereby permitting longer surgery.
Cryopreservation: The preservation of cells by keeping them at extremely low temperatures.
Cryosurgery: Surgery that involves the freezing of tissue to be treated or operated on.
[ See also Cryogenics ]