Cryobiology is a branch of biology that studies the effects of low temperature (including profound hypothermia) on the biological effects and their applications. Generally the so-called low temperature refers to about 0 degree Celsius; profound hypothermia generally refers to the following -80 degree Celsius. Cryobiology mainly researches plant frost in the past and the main bacteria and insects on the low temperature tolerance. Since the 20th century, begins the low temperature processing research of the biological and biological materials as food and work gradually enters the cell and molecular level, the research results are widely used in biological products, livestock, and some organs, especially cryopreservation of blood cells.
2. Frozen and Organisms
The organism's metabolism slows down as the temperature decreases. If the low temperature above 0 degrees Celsius, the slow process is generally reversible, that is, after the temperature rise, the rate of metabolism will be restored. But when the temperature falls below the freezing point, the living organisms are often damaged by freezing. Because all of the humoral contain large amounts of water (general in about 80%), organelles also suspended in aqueous solution, metabolic processes are carried out in aqueous solution or film and aqueous solution interface, so in the process of freezing the, on the one hand water crystal - Crystal hardness larger, for the fine structure of the organism will cause mechanical damage due to; on the other hand, as the water freezes, the cells lost a large number of available water, resulting in dehydration, so that the fine structure is destroyed.
3. Low Temperature Protection
Low temperature slows down the metabolism, so people have long tried to use this feature in order to preserve the living organisms for long time. Since the sixties, great achievements have been made in this area. The main method is: using the additive and quick frozen, to prevent the formation of ice crystals, even the formation of small ice crystals, does not cause mechanical damage. Commonly used additives are glycerol and some compounds such as mannitol; the role of the water is not easy to freeze. Frozen is the living body in a very short time, immediately dropped to the temperature of liquid nitrogen (about -195 degrees Celsius), so that the rapid solidification of water, in order to avoid the formation of ice crystals. The use of additives can not completely prevent the freezing; single frozen although it can avoid the formation of large ice crystals in the cooling, but cannot avoid the formation of large ice crystals in the temperature rise. The proper combination of the two only, in order to avoid damage of low temperature on the organism; II freeze drying, namely in the solid state, relying on vacuum drying sublimate water and to prevent rapid cooling and solidification of the liquid in the temperature rise and the formation of ice crystals. The biological samples can be stored at room temperature after freeze drying, and it is a kind of ideal preservation method. However, when the temperature is too low, the sublimation is too slow, the temperature is too high and it is difficult to avoid the formation of ice crystals, and complete dehydration will bring some non recoverable damage to the complex organisms. So it is currently only used to preserve biological products (such as certain drugs, serum preparations), dairy, food, as well as bacteria and viruses (see strain preservation), and so on. Compared with the ordinary method of drying, freeze drying method has the advantages of is can be better to save the activity of biological products, freeze-drying pharmaceuticals, serum preparation easily dissolved, food shape and color, smell, taste and other can also well preserved. If in about -80 degree Celsius of cryopreservation, although there is no freeze dried convenient, but little damage to the organism, for preservation of microbial strains, the higher animals, sperm, eggs, whole blood and organ storage, even in its early stages of development of mammalian embryos.
Cryobiochemistry is a new discipline which studies the biological chemistry of life activity under low temperature, and it is the important foundation of low temperature biology. For example, in some of the state of hibernation insect body fluid, the glycerol content can be as high as 25%, so that in the case of -35 degrees Celsius will not freeze. On the other hand, the changes of some biochemical reactions at room temperature are studied by using the change of low temperature, such as the change of the space conformation of the enzyme, the protein and the nucleic acid in the solution. Some changes at room temperature within a thousandth of a second time can be completed, with the general method to investigate, and in the presence of additives the temperature dropped to -40 degree Celsius solution, reaction speed much slower is available with the conventional method used in this study.