Cryopreservation

Under cryopreservation (from Greek κρύος, kryos = cold and Latin conservare = receive, retain ) refers to the storage of cells or tissues by freezing in liquid nitrogen. Using this method, it is possible to maintain the vitality of the cells almost unlimited, although the biological system enters the state of aggregation of a solid. Cryopreservation can be applied to both plant cells and in animal cells, in humans as well as in sperm, ova and embryos. The storage takes place in so-called cryo-banks.

The preserved cells can be obtained over a very long period of time in a sort of hibernation, in which all metabolic processes come almost to a standstill. After thawing, the cells can resume their normal physiological processes again. Embryos can then be transferred, for example, into the uterine cavity.

Individual cells can be frozen so fast that the water forms only small ice crystals. For larger, multicellular organisms, however, formed during freezing due to the low temperature reduction in core ice crystals, which are so large that they break the cell walls and thus destroy irreparably. The freezing of strawberries in the freezer illustrates the cell damage during freezing vividly: After thawing, the act mushy strawberries - they have lost water which has leaked from the damaged cells.

Cryopreservation works nowadays for cell samples to small organs, if the sample freezes with the help of the right mix of anti-freeze very quickly, so for example with liquid nitrogen to 77 K (-196 ° C ) cooling ( glaze ). Various mosses can be cryopreserved at -135 ° C for several years without losing their capacity to regenerate.

There are frogs like the wood frog or insect as the gall midge that survive freezing in winter to a certain critical temperature due to the body's own anti-freeze agent ( urea). However, larger organs and organisms suffer during cryopreservation damage that can not be solved with today's means. A success or failure of cryonics will be therefore be assessed in retrospect.