Cryo-preservation or cryo-conservation is a process where organelles, tissues, extracellular matrix, organs, or any other biological constructs susceptible to damage caused by unregulated chemical kinetics are preserved by cooling to low temperatures. At low enough temperatures, any enzymatic or chemical activity which might cause damage to the biological material in question is stopped. Cryopreservation methods seek to reach low temperatures without causing additional damage caused by the formation of ice crystals during freezing. Traditional cryopreservation has relied on coating the material to be frozen with a class of molecules termed cryoprotectants. New methods are being investigated due to the inherent toxicity of many cryoprotectants. By default it should be considered that cryopreservation alters or compromises the structure and function of cells unless it is proven otherwise for a particular cell population. Cryoconservation of animal genetic resources is the process in which animal genetic material is collected and stored with the intention of conservation of the breed.
Water-bears, microscopic multicellular organisms, can survive freezing by replacing most of their internal water with the sugar trehalose, preventing it from crystallization that otherwise damages cell membranes. Mixtures of solutes can achieve similar effects; some solutes, including salts, have the disadvantage that they may be toxic at intense concentrations. In addition to the water-bear, wood frogs can tolerate the freezing of their blood and other tissues. Urea is accumulated in tissues in preparation for overwintering, liver glycogen is converted in large quantities to glucose in response to internal ice formation. Both urea and glucose act as "cryoprotectants" to limit the amount of ice that forms and to reduce osmotic shrinkage of cells. Frogs can survive many freeze/thaw events during winter if no more than about 65% of the total body water freezes. Research exploring the phenomenon of "freezing frogs" has been performed by the Canadian researcher, Dr. Kenneth B. Storey. Freeze tolerance, in which organisms survive the winter by freezing solid and ceasing life functions, is known in a few vertebrates: five species of frogs, one of salamanders, one of snakes and three of turtles.
Snapping turtles Chelydra serpentina and wall lizards Podarcis muralis survive nominal freezing but it has not been established to be adaptive for overwintering. In the case of Rana sylvatica one cryopreservant is ordinary glucose, which increases in concentration by 19 mmol/l when the frogs are cooled slowly. One of the most important early theoreticians of cryopreservation was James Lovelock. In 1953, he suggested that damage to red blood cells during freezing was due to osmotic stress, that increasing the salt concentration in a dehydrating cell might damage it. In the mid-1950s, he experimented with the cryopreservation of rodents, determining that hamsters could be frozen with 60% of the water in the brain crystallized into ice with no adverse effects; this work led other scientists to attempt the short-term freezing of rats by 1955, which were active 4 to 7 days after being revived. Cryopreservation was applied to humans beginning in 1954 with three pregnancies resulting from the insemination of frozen sperm.
Fowl sperm was cryopreserved in 1957 by a team of scientists in the UK directed by Christopher Polge. However, the rapid immersion of the samples in liquid nitrogen did not, for certain samples—such as some types of embryos, bone marrow and stem cells—produce the necessary viability to make them usable after thawing. Increased understanding of the mechanism of freezing injury to cells emphasised the importance of controlled or slow cooling to obtain maximum survival on thawing of the living cells. A controlled-rate cooling process, allowing biological samples to equilibrate to optimal physical parameters osmotically in a cryoprotectant before cooling in a predetermined, controlled way proved necessary; the ability of cryoprotectants, in the early cases glycerol, to protect cells from freezing injury was discovered accidentally. Freezing injury has two aspects: direct damage from the ice crystals and secondary damage caused by the increase in concentration of solutes as progressively more ice is formed.
During 1963, Peter Mazur, at Oak Ridge National Laboratory in the U. S. demonstrated that lethal intracellular freezing could be avoided if cooling was slow enough to permit sufficient water to leave the cell during progressive freezing of the extracellular fluid. That rate differs between cells of differing size and water permeability: a typical cooling rate around 1 °C/minute is appropriate for many mammalian cells after treatment with cryoprotectants such as glycerol or dimethyl sulphoxide, but the rate is not a universal optimum. Storage at low temperatures is presumed to provide an indefinite longevity to cells, although the actual effective life is rather difficult to prove. Researchers experimenting with dried seeds found that there was noticeable variability of deterioration when samples were kept at different temperatures – ultra-cold temperatures. Temperatures less than the glass transition point of polyol's water solutions, around −136 °C, seem to be accepted as the range where biological activity substantially slows, −196 °C, the boiling point of liquid nitrogen, is the preferred temperature for storing impor
Hibernation is a state of inactivity and metabolic depression in endotherms. Hibernation refers to a season of heterothermy characterized by low body temperature, slow breathing and heart rate, low metabolic rate, it is most observed during the winter months. Although traditionally reserved for "deep" hibernators such as rodents, the term has been redefined to include animals such as bears and is now applied based on active metabolic suppression rather than any absolute decline in body temperature. Many experts believe that the processes of daily torpor and hibernation form a continuum and utilize similar mechanisms; the equivalent during the summer months is aestivation. Associated with low temperatures, hibernation functions to conserve energy when sufficient food is unavailable. To achieve this energy saving, an endothermic animal decreases its metabolic rate and thereby its body temperature. Hibernation may last days, weeks, or months depending on the species, ambient temperature, time of year, the individual's body condition.
Before entering hibernation, animals need to store enough energy to last through the duration of their dormant period as long as the entire winter. Larger species become hyperphagic, eating a large amount of food and storing the energy in fat deposits. In many small species, food caching replaces becoming fat; some species of mammals hibernate while gestating young, which are born either while the mother hibernates or shortly afterwards. For example, female polar bears go into hibernation during the cold winter months in order to give birth to their offspring; the pregnant mothers increase their body mass prior to hibernation, this increase is further reflected in the weight of the offspring. The fat accumulation enables them to provide a sufficiently warm and nurturing environment for their newborns. During hibernation, they subsequently lose 15–27% of their pre-hibernation weight by using their stored fats for energy. True hibernation is restricted to endotherms. Still, many ectothermic animals undergo periods of dormancy which are sometimes confused with hibernation.
Some reptile species are said to brumate, but possible similarities between brumation and hibernation are not established. Many insects, such as the wasp Polistes exclamans, exhibit periods of dormancy which have been referred to as hibernation, despite their ectothermy. Obligate hibernators are animals that spontaneously, annually, enter hibernation regardless of ambient temperature and access to food. Obligate hibernators include many species of ground squirrels, other rodents, mouse lemurs, European hedgehogs and other insectivores and marsupials These species undergo what has been traditionally called "hibernation": a physiological state wherein the body temperature drops to near ambient temperature, heart and respiration rates slow drastically; the typical winter season for obligate hibernators is characterized by periods of torpor interrupted by periodic, euthermic arousals, during which body temperatures and heart rates are restored to more typical levels. The cause and purpose of these arousals is still not clear.
One favored hypothesis is that hibernators build a "sleep debt" during hibernation, so must warm up to sleep. This has been supported by evidence in the Arctic ground squirrel. Other theories postulate that brief periods of high body temperature during hibernation allow the animal to restore its available energy sources or to initiate an immune response. Hibernating Arctic ground squirrels may exhibit abdominal temperatures as low as −2.9 °C, maintaining sub-zero abdominal temperatures for more than three weeks at a time, although the temperatures at the head and neck remain at 0 °C or above. There was a question of whether or not bears hibernate since they experience only a modest decline in body temperature compared with the much larger decreases seen in other hibernators. Many researchers thought that their deep sleep was not comparable with true, deep hibernation, but recent research has refuted this theory in captive black bears. Unlike obligate hibernators, facultative hibernators only enter hibernation when either cold-stressed, food-deprived, or both.
A good example of the differences between these two types of hibernation can be seen in prairie dogs: the white-tailed prairie dog is an obligate hibernator and the related black-tailed prairie dog is a facultative hibernator. While hibernation has long been studied in rodents, namely ground squirrels, no primate or tropical mammal was known to hibernate until the discovery of hibernation in the fat-tailed dwarf lemur of Madagascar, which hibernates in tree holes for seven months of the year. Malagasy winter temperatures sometimes rise to over 30 °C, so hibernation is not an adaptation to low ambient temperatures; the hibernation of this lemur is dependent on the thermal behaviour of its tree hole: if the hole is poorly insulated, the lemur's body temperature fluctuates passively following the ambient temperature. Dausmann found that hypometabolism in hibernating animals is not coupled with low body temperature. Hibernating bears are able to recycle their proteins and urine, allowing them both to stop urinating for months and to avoid muscl
A clathrate is a chemical substance consisting of a lattice that traps or contains molecules. The word clathrate is derived from the Latin clatratus meaning with a lattice. Traditionally, clathrate compounds are polymeric and envelop the guest molecule, but in modern usage clathrates include host–guest complexes and inclusion compounds. According to IUPAC, clathrates are "Inclusion compounds in which the guest molecule is in a cage formed by the host molecule or by a lattice of host molecules." Traditionally clathrate compounds refer to polymeric hosts containing molecular guests. More the term refers to many molecular hosts, including calixarenes and cyclodextrins and some inorganic polymers such as zeolites; the natural silica clathrate mineral, chibaite was described from Japan. Many clathrates are derived from organic hydrogen-bonded frameworks; these frameworks are prepared from molecules that "self-associate" by multiple hydrogen-bonding interactions. The most famous clathrates are methane clathrates where the hydrogen-bonded framework is contributed by water and the guest molecules are methane.
Large amounts of methane frozen in this form exist both in permafrost formations and under the ocean sea-bed. Other hydrogen-bonded networks are derived from hydroquinone and thiourea. A much studied host molecule is Dianin's compound. Hofmann compounds are coordination polymers with the formula Ni4·Ni2; these materials crystallize with small aromatic guests, this selectivity has been exploited commercially for the separation of these hydrocarbons. Metal organic frameworks form clathrates. Photolytically-sensitive caged compounds have been examined as containers for releasing a drug or reagent. Clathrate hydrates were discovered in 1810 by Humphry Davy. Clathrates were studied by P. Pfeiffer in 1927 and in 1930, E. Hertel defined "molecular compounds" as substances decomposed into individual components following the mass action law in solution or gas state. In 1945, H. M. Powell named them clathrates. Inclusion compounds are molecules, whereas clathrates are polymeric. Intercalation compounds are not 3-dimensional, unlike clathrate compounds.
Fluid statics or hydrostatics is the branch of fluid mechanics that studies "fluids at rest and the pressure in a fluid or exerted by a fluid on an immersed body". It encompasses the study of the conditions under which fluids are at rest in stable equilibrium as opposed to fluid dynamics, the study of fluids in motion. Hydrostatics are categorized as a part of the fluid statics, the study of all fluids, incompressible or not, at rest. Hydrostatics is fundamental to hydraulics, the engineering of equipment for storing and using fluids, it is relevant to geophysics and astrophysics, to meteorology, to medicine, many other fields. Hydrostatics offers physical explanations for many phenomena of everyday life, such as why atmospheric pressure changes with altitude, why wood and oil float on water, why the surface of still water is always level; some principles of hydrostatics have been known in an empirical and intuitive sense since antiquity, by the builders of boats, cisterns and fountains. Archimedes is credited with the discovery of Archimedes' Principle, which relates the buoyancy force on an object, submerged in a fluid to the weight of fluid displaced by the object.
The Roman engineer Vitruvius warned readers about lead pipes bursting under hydrostatic pressure. The concept of pressure and the way it is transmitted by fluids was formulated by the French mathematician and philosopher Blaise Pascal in 1647; the "fair cup" or Pythagorean cup, which dates from about the 6th century BC, is a hydraulic technology whose invention is credited to the Greek mathematician and geometer Pythagoras. It was used as a learning tool; the cup consists of a line carved into the interior of the cup, a small vertical pipe in the center of the cup that leads to the bottom. The height of this pipe is the same as the line carved into the interior of the cup; the cup may be filled to the line without any fluid passing into the pipe in the center of the cup. However, when the amount of fluid exceeds this fill line, fluid will overflow into the pipe in the center of the cup. Due to the drag that molecules exert on one another, the cup will be emptied. Heron's fountain is a device invented by Heron of Alexandria that consists of a jet of fluid being fed by a reservoir of fluid.
The fountain is constructed in such a way that the height of the jet exceeds the height of the fluid in the reservoir in violation of principles of hydrostatic pressure. The device consisted of an opening and two containers arranged one above the other; the intermediate pot, sealed, was filled with fluid, several cannula connecting the various vessels. Trapped air inside the vessels induces a jet of water out of a nozzle, emptying all water from the intermediate reservoir. Pascal made contributions to developments in both hydrodynamics. Pascal's Law is a fundamental principle of fluid mechanics that states that any pressure applied to the surface of a fluid is transmitted uniformly throughout the fluid in all directions, in such a way that initial variations in pressure are not changed. Due to the fundamental nature of fluids, a fluid cannot remain at rest under the presence of a shear stress. However, fluids can exert pressure normal to any contacting surface. If a point in the fluid is thought of as an infinitesimally small cube it follows from the principles of equilibrium that the pressure on every side of this unit of fluid must be equal.
If this were not the case, the fluid would move in the direction of the resulting force. Thus, the pressure on a fluid at rest is isotropic; this characteristic allows fluids to transmit force through the length of tubes. This principle was first formulated, in a extended form, by Blaise Pascal, is now called Pascal's law. In a fluid at rest, all frictional and inertial stresses vanish and the state of stress of the system is called hydrostatic; when this condition of V = 0 is applied to the Navier-Stokes equation, the gradient of pressure becomes a function of body forces only. For a barotropic fluid in a conservative force field like a gravitational force field, pressure exerted by a fluid at equilibrium becomes a function of force exerted by gravity; the hydrostatic pressure can be determined from a control volume analysis of an infinitesimally small cube of fluid. Since pressure is defined as the force exerted on a test area, the only force acting on any such small cube of fluid is the weight of the fluid column above it, hydrostatic pressure can be calculated according to the following formula: p − p = 1 A ∫ z 0 z d z ′ ∬ A d x ′ d y ′ ρ g = ∫ z 0 z d z ′ ρ g, where: p is the hydrostatic pressure, ρ is the fluid density