Cryobiology

Cryobiology is the scientific study of the effects of freezing and sub-freezing temperatures on biological fluids, cells, and tissues. It is an extension of cryogenics, which is the study of the properties of matter at very low temperatures.

Cryobiological techniques have application in genetic research, livestock breeding, infertility treatment, and organ transplantation.

A related field, cryogenics, is devoted to the study of the effects of low temperature. Cryogenic preservation of humans has been proposed; it is envisioned that maintaining someone in what could be considered a state of suspended animation could allow those with a currently non-curable disease to be revived at some point in the future when a cure has been found. Currently, however, despite claims to the contrary, this process is impossible because of the irreparable cell damage that occurs during the freezing process.

The terms cryobiology and cryogenics are derived from the Greek kryos, meaning icy cold. Temperatures used in cryogenics range from–148°F (–100°C) to near absolute zero–459.67°F (–273.15°C). Such ultra-low temperatures can be achieved by the use of supercooled gases. The study of these gases dates back to 1877, when Swiss physicist Raoul Pictet (1846–1929) and French physicist/chemist Louis Cailletet (1832– 1913) first learned how to liquefy oxygen. Although they worked independently and used different methods, both men discovered that oxygen could be liquefied at 297.67°F (–183.15°C). Soon after, other researchers liquefied nitrogen at–321.07°F(–196.15°C).

Other breakthroughs in cryogenics included James Dewar’s invention of the vacuum flask in 1898. Dewar’s double-walled vacuum storage vessel allowed liquefied gases to be more readily studied. In the last 100 years, a variety of other methods for insulating super-cooled fluids have been developed.

In the twentieth century, scientists began applying cryogenic techniques to biological systems. They explored methods for treating blood, semen, tissue, and organs with ultra-low temperatures. This research has resulted in advances in genetic research, livestock breeding, infertility treatment, and organ transplantation.

Cryobiology has provided an inexpensive way to freeze and store the embryos of different strains of research laboratory animals, such as mice. Maintaining a breeding colony of research animals can be expensive, and cryogenic storage of embryos can reduce cost considerably. When the animals are needed, they can be thawed and implanted. It is this ability that has inspired some to consider cryobiology as a means of preserving humans.

In agriculture, cryopreservation allows livestock breeders to mass produce the embryos of genetically desirable cattle. For example, hundreds of eggs can be harvested from a single prize dairy cow and frozen for later implantation in other mothers. Using similar techniques, pigs that are too fat to reproduce on their own can be artificially implanted with embryos developed from frozen eggs and sperm. In addition, cryobiologists are examining the possibility of increasing buffalo herds by freezing bison embryos and later implanting them into cows to give birth.

Cryobiology has met with great success in the treatment of human infertility. The use of frozen sperm, eggs, and embryos increases the success rate of fertility treatments because it allows doctors to obtain a large number of samples that can be stored for future fertilization. Techniques for freezing sperm were relatively easy to develop, and in 1953, the first baby fertilized with previously frozen sperm was born. The process for freezing embryos is much more complicated, however. It involves removing water from the cells and replacing it with an organic antifreeze that prevents the formation of ice crystals that can cause cells to burst. Advances over the last few decades have made this technique highly successful, and in 1984, the first baby was born from a previously frozen embryo. Freezing eggs is an even more difficult challenge because the fragile membrane structure that surrounds the eggs makes them difficult to freeze without causing severe damage. However, eggs have been successfully frozen using a chemical solution similar to the ovaries’ natural fluids. The technique has been used to freeze eggs, which were later thawed and used to impregnate a woman. In 1997, the first birth resulting from frozen eggs was recorded.

Organ storage is another important area of cryo-biological research. Using conventional methods, organs can only be stored for very short periods of time. For example, a kidney can be kept for only three days, a liver for no more than 36 hours, and hearts and lungs for no more than six hours. If these organs could be frozen without subcellular damage, storage times would be lengthened almost indefinitely. Although researchers have made great advances, they have not yet perfected the process of freezing and reviving organs. The problem they face is that the formation of ice crystals can damage fragile tissue. However, researchers have devised a cryopreservant liquid that protects the organs during the freezing process. In another development, a so-called antifreeze protein has been successfully used to freeze and revive rat livers. The protein is derived from fish living in the Arctic that has evolved to survive in very cold water. An antifreeze protein alters the structure of ice crystal in order to be less damaging to cells. A technique called vitrification cools organs so quickly that their molecules do not have time to form damaging ice crystals. Continued success in these areas may one day lead to reliable methods of freezing and storing organs for future transplant.