Cryoprotectant
Encyclopedia
A cryoprotectant is a substance that is used to protect biological tissue
from freezing
damage (damage due to ice
formation). Arctic
and Antarctic
insect
s, fish
, amphibian
s and reptile
s create cryoprotectants (antifreeze compounds
and antifreeze protein
s) in their bodies to minimize freezing damage during cold winter periods. Insects most often use sugar
s or polyol
s as cryoprotectants. Arctic frog
s use glucose
, but Arctic salamander
s create glycerol
in their liver
s for use as cryoprotectant. Cryoprotectants operate simply by increasing the solute concentration in cells. However, in order to be biologically viable they must (1) easily penetrate cells, and (2) not be toxic to the cell.
Conventional cryoprotectants are glycols (alcohol
s containing at least two hydroxyl
groups), such as ethylene glycol
, propylene glycol
and glycerol
. Ethylene glycol
is commonly used as automobile antifreeze
and propylene glycol
has been used to reduce ice formation in ice cream
. Dimethyl sulfoxide
(DMSO) is also regarded as a conventional cryoprotectant. Glycerol and DMSO have been used for decades by cryobiologist
s to reduce ice formation in sperm
and embryo
s that are cold-preserved in liquid nitrogen
.
Mixtures of cryoprotectants have less toxicity
and are more effective than single-agent cryoprotectants. A mixture of formamide
with DMSO, propylene glycol and a colloid
was for many years the most effective of all artificially created cryoprotectants. Cryoprotectant mixtures have been used for vitrification, i.e. solidification without any crystal ice formation. Vitrification
has important application in preserving embryos, biological
tissues and organ
s for transplant
. Vitrification is also used in cryonics
in an effort to eliminate freezing damage.
Some cryoprotectants function by lowering a solution's or a material's glass transition temperature. In this way, the cryoprotectants prevent actual freezing, and the solution maintains some flexibility in a glassy phase. Many cryoprotectants also function by forming hydrogen bonds with biological molecules as water molecules are displaced. Hydrogen bonding in aqueous solutions is important for proper protein and DNA function. Thus, as the cryoprotectant replaces the water molecules, the biological material retains its native physiological structure (and function), although they are no longer immersed in an aqueous environment. This preservation strategy is most often observed in anhydrobiosis
.
Cryoprotectants are also used to preserve foods. These compounds are typically sugars that are inexpensive and do not pose any toxicity concerns. For example, many (raw) frozen chicken products contain a "solution" of water, sucrose, and sodium phosphates.
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...
from freezing
Freezing
Freezing or solidification is a phase change in which a liquid turns into a solid when its temperature is lowered below its freezing point. The reverse process is melting....
damage (damage due to ice
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
formation). Arctic
Arctic
The Arctic is a region located at the northern-most part of the Earth. The Arctic consists of the Arctic Ocean and parts of Canada, Russia, Greenland, the United States, Norway, Sweden, Finland, and Iceland. The Arctic region consists of a vast, ice-covered ocean, surrounded by treeless permafrost...
and Antarctic
Antarctic
The Antarctic is the region around the Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica and the ice shelves, waters and island territories in the Southern Ocean situated south of the Antarctic Convergence...
insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, fish
Fish
Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...
, amphibian
Amphibian
Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...
s and reptile
Reptile
Reptiles are members of a class of air-breathing, ectothermic vertebrates which are characterized by laying shelled eggs , and having skin covered in scales and/or scutes. They are tetrapods, either having four limbs or being descended from four-limbed ancestors...
s create cryoprotectants (antifreeze compounds
Antifreeze
Antifreeze is a freeze preventive used in internal combustion engines and other heat transfer applications, such as HVAC chillers and solar water heaters....
and antifreeze protein
Antifreeze protein
Antifreeze proteins or ice structuring proteins refer to a class of polypeptides produced by certain vertebrates, plants, fungi and bacteria that permit their survival in subzero environments. AFPs bind to small ice crystals to inhibit growth and recrystallization of ice that would otherwise be...
s) in their bodies to minimize freezing damage during cold winter periods. Insects most often use sugar
Sugar
Sugar is a class of edible crystalline carbohydrates, mainly sucrose, lactose, and fructose, characterized by a sweet flavor.Sucrose in its refined form primarily comes from sugar cane and sugar beet...
s or polyol
Polyol
A polyol is an alcohol containing multiple hydroxyl groups. In two technological disciplines the term "polyol" has a special meaning: food science and polymer chemistry.- Polyols in food science :...
s as cryoprotectants. Arctic frog
Frog
Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...
s use glucose
Glucose
Glucose is a simple sugar and an important carbohydrate in biology. Cells use it as the primary source of energy and a metabolic intermediate...
, but Arctic salamander
Salamander
Salamander is a common name of approximately 500 species of amphibians. They are typically characterized by a superficially lizard-like appearance, with their slender bodies, short noses, and long tails. All known fossils and extinct species fall under the order Caudata, while sometimes the extant...
s create glycerol
Glycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
in their liver
Liver
The liver is a vital organ present in vertebrates and some other animals. It has a wide range of functions, including detoxification, protein synthesis, and production of biochemicals necessary for digestion...
s for use as cryoprotectant. Cryoprotectants operate simply by increasing the solute concentration in cells. However, in order to be biologically viable they must (1) easily penetrate cells, and (2) not be toxic to the cell.
Conventional cryoprotectants are glycols (alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s containing at least two hydroxyl
Hydroxide
Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...
groups), such as ethylene glycol
Ethylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...
, propylene glycol
Propylene glycol
Propylene glycol, also called 1,2-propanediol or propane-1,2-diol, is an organic compound with formula C3H8O2 or HO-CH2-CHOH-CH3...
and glycerol
Glycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
. Ethylene glycol
Ethylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...
is commonly used as automobile antifreeze
Antifreeze
Antifreeze is a freeze preventive used in internal combustion engines and other heat transfer applications, such as HVAC chillers and solar water heaters....
and propylene glycol
Propylene glycol
Propylene glycol, also called 1,2-propanediol or propane-1,2-diol, is an organic compound with formula C3H8O2 or HO-CH2-CHOH-CH3...
has been used to reduce ice formation in ice cream
Ice cream
Ice cream is a frozen dessert usually made from dairy products, such as milk and cream, and often combined with fruits or other ingredients and flavours. Most varieties contain sugar, although some are made with other sweeteners...
. Dimethyl sulfoxide
Dimethyl sulfoxide
Dimethyl sulfoxide is an organosulfur compound with the formula 2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water...
(DMSO) is also regarded as a conventional cryoprotectant. Glycerol and DMSO have been used for decades by cryobiologist
Cryobiology
Cryobiology is the branch of biology that studies the effects of low temperatures on living things. The word cryobiology is derived from the Greek words "cryo" = cold, "bios" = life, and "logos" = science. In practice, cryobiology is the study of biological material or systems at temperatures below...
s to reduce ice formation in sperm
Spermatozoon
A spermatozoon is a motile sperm cell, or moving form of the haploid cell that is the male gamete. A spermatozoon joins an ovum to form a zygote...
and embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s that are cold-preserved in liquid nitrogen
Liquid nitrogen
Liquid nitrogen is nitrogen in a liquid state at a very low temperature. It is produced industrially by fractional distillation of liquid air. Liquid nitrogen is a colourless clear liquid with density of 0.807 g/mL at its boiling point and a dielectric constant of 1.4...
.
Mixtures of cryoprotectants have less toxicity
Toxicity
Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...
and are more effective than single-agent cryoprotectants. A mixture of formamide
Formamide
Formamide, also known as methanamide, is an amide derived from formic acid. It is a clear liquid which is miscible with water and has an ammonia-like odor. It is used primarily for manufacturing sulfa drugs and synthesizing vitamins and as a softener for paper and fiber...
with DMSO, propylene glycol and a colloid
Colloid
A colloid is a substance microscopically dispersed evenly throughout another substance.A colloidal system consists of two separate phases: a dispersed phase and a continuous phase . A colloidal system may be solid, liquid, or gaseous.Many familiar substances are colloids, as shown in the chart below...
was for many years the most effective of all artificially created cryoprotectants. Cryoprotectant mixtures have been used for vitrification, i.e. solidification without any crystal ice formation. Vitrification
Vitrification
Vitrification is the transformation of a substance into a glass. Usually, it is achieved by rapidly cooling a liquid through the glass transition. Certain chemical reactions also result in glasses...
has important application in preserving embryos, biological
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
tissues and organ
Organ (anatomy)
In biology, an organ is a collection of tissues joined in structural unit to serve a common function. Usually there is a main tissue and sporadic tissues . The main tissue is the one that is unique for the specific organ. For example, main tissue in the heart is the myocardium, while sporadic are...
s for transplant
Organ transplant
Organ transplantation is the moving of an organ from one body to another or from a donor site on the patient's own body, for the purpose of replacing the recipient's damaged or absent organ. The emerging field of regenerative medicine is allowing scientists and engineers to create organs to be...
. Vitrification is also used in cryonics
Cryonics
Cryonics is the low-temperature preservation of humans and animals who can no longer be sustained by contemporary medicine, with the hope that healing and resuscitation may be possible in the future. Cryopreservation of people or large animals is not reversible with current technology...
in an effort to eliminate freezing damage.
Some cryoprotectants function by lowering a solution's or a material's glass transition temperature. In this way, the cryoprotectants prevent actual freezing, and the solution maintains some flexibility in a glassy phase. Many cryoprotectants also function by forming hydrogen bonds with biological molecules as water molecules are displaced. Hydrogen bonding in aqueous solutions is important for proper protein and DNA function. Thus, as the cryoprotectant replaces the water molecules, the biological material retains its native physiological structure (and function), although they are no longer immersed in an aqueous environment. This preservation strategy is most often observed in anhydrobiosis
Cryptobiosis
Cryptobiosis is an ametabolic state of life entered by an organism in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all metabolic procedures stop, preventing reproduction, development, and repair...
.
Cryoprotectants are also used to preserve foods. These compounds are typically sugars that are inexpensive and do not pose any toxicity concerns. For example, many (raw) frozen chicken products contain a "solution" of water, sucrose, and sodium phosphates.
Common cryoprotectants
- DMSODimethyl sulfoxideDimethyl sulfoxide is an organosulfur compound with the formula 2SO. This colorless liquid is an important polar aprotic solvent that dissolves both polar and nonpolar compounds and is miscible in a wide range of organic solvents as well as water...
(dimethyl sulfoxide) - Ethylene glycolEthylene glycolEthylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...
- GlycerolGlycerolGlycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
- 2-Methyl-2,4-pentanediol2-Methyl-2,4-pentanediol2-Methyl-2,4-pentanediol is a chemical used in industrial coatings and as a chemical intermediate. Total European and USA production was 15000 tonnes in 2000...
(MPD) - Propylene glycolPropylene glycolPropylene glycol, also called 1,2-propanediol or propane-1,2-diol, is an organic compound with formula C3H8O2 or HO-CH2-CHOH-CH3...
- SucroseSucroseSucrose is the organic compound commonly known as table sugar and sometimes called saccharose. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in human nutrition. The molecule is a disaccharide composed of glucose and fructose with the molecular formula...
See also
- Antifreeze proteinAntifreeze proteinAntifreeze proteins or ice structuring proteins refer to a class of polypeptides produced by certain vertebrates, plants, fungi and bacteria that permit their survival in subzero environments. AFPs bind to small ice crystals to inhibit growth and recrystallization of ice that would otherwise be...
- LyophilizationFreeze dryingFreeze-drying is a dehydration process typically used to preserve a perishable material or make the material more convenient for transport...
- List of emerging technologies
- CryopreservationCryopreservationCryopreservation is a process where cells or whole tissues are preserved by cooling to low sub-zero temperatures, such as 77 K or −196 °C . At these low temperatures, any biological activity, including the biochemical reactions that would lead to cell death, is effectively stopped...