Monthly Archives: March 2021

Process where biological matter is preserved by cooling to very low temperatures

Cryo-preservation or cryo-conservation is a process where organelles, cells, tissues, extracellular matrix, organs, or any other biological constructs susceptible to damage caused by unregulated chemical kinetics are preserved by cooling to very low temperatures[1] (typically 80C using solid carbon dioxide or 196C using liquid nitrogen). At low enough temperatures, any enzymatic or chemical activity which might cause damage to the biological material in question is effectively 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.[2] Cryoconservation of animal genetic resources is done with the intention of conservation of the breed.

Water-bears (Tardigrada), 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, and 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 primarily by the Canadian researcher, Dr. Kenneth B. Storey.[citation needed]

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 (Rana sylvatica, Pseudacris triseriata, Hyla crucifer, Hyla versicolor, Hyla chrysoscelis), one of salamanders (Salamandrella keyserlingii), one of snakes (Thamnophis sirtalis) and three of turtles (Chrysemys picta, Terrapene carolina, Terrapene ornata).[3] Snapping turtles Chelydra serpentina and wall lizards Podarcis muralis also 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 approximately 19mmol/l when the frogs are cooled slowly.[3]

One early theoretician of cryopreservation was James Lovelock. In 1953, he suggested that damage to red blood cells during freezing was due to osmotic stress,[4] and that increasing the salt concentration in a dehydrating cell might damage it.[5][6] 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; other organs were shown to be susceptible to damage.[7] This work led other scientists to attempt the short-term freezing of rats by 1955, which were fully active 4 to 7 days after being revived.[8]

Cryopreservation was applied to humans beginning in 1954 with three pregnancies resulting from the insemination of previously frozen sperm.[9] Fowl sperm was cryopreserved in 1957 by a team of scientists in the UK directed by Christopher Polge.[10] 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 1C/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.[11]

The first human body to be frozen with the hope of future revival was James Bedford's, a few hours after his cancer-caused death in 1967.[12] Bedford is the only cryonics patient frozen before 1974 still preserved today.[13]

Storage at very 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 even ultra-cold temperatures. Temperatures less than the glass transition point (Tg) of polyol's water solutions, around 136C (137K; 213F), seem to be accepted as the range where biological activity very substantially slows, and 196C (77K; 321F), the boiling point of liquid nitrogen, is the preferred temperature for storing important specimens. While refrigerators, freezers and extra-cold freezers are used for many items, generally the ultra-cold of liquid nitrogen is required for successful preservation of the more complex biological structures to virtually stop all biological activity.

Phenomena which can cause damage to cells during cryopreservation mainly occur during the freezing stage, and include solution effects, extracellular ice formation, dehydration, and intracellular ice formation. Many of these effects can be reduced by cryoprotectants.Once the preserved material has become frozen, it is relatively safe from further damage.[14]

The main techniques to prevent cryopreservation damages are a well established combination of controlled rate and slow freezing and a newer flash-freezing process known as vitrification.

Controlled-rate and slow freezing, also known as slow programmable freezing (SPF),[15] is a set of well established techniques developed during the early 1970s which enabled the first human embryo frozen birth Zoe Leyland during 1984. Since then, machines that freeze biological samples using programmable sequences, or controlled rates, have been used all over the world for human, animal and cell biology "freezing down" a sample to better preserve it for eventual thawing, before it is frozen, or cryopreserved, in liquid nitrogen. Such machines are used for freezing oocytes, skin, blood products, embryo, sperm, stem cells and general tissue preservation in hospitals, veterinary practices and research laboratories around the world. As an example, the number of live births from frozen embryos 'slow frozen' is estimated at some 300,000 to 400,000 or 20% of the estimated 3 million in vitro fertilisation (IVF) births.[16]

Lethal intracellular freezing can be avoided if cooling is slow enough to permit sufficient water to leave the cell during progressive freezing of the extracellular fluid. To minimize the growth of extracellular ice crystals and recrystallization,[17] biomaterials such as alginates, polyvinyl alcohol or chitosan can be used to impede ice crystal growth along with traditional small molecule cryoprotectants.[2] That rate differs between cells of differing size and water permeability: a typical cooling rate of about 1C/minute is appropriate for many mammalian cells after treatment with cryoprotectants such as glycerol or dimethyl sulfoxide, but the rate is not a universal optimum. The 1C / minute rate can be achieved by using devices such as a rate-controlled freezer or a benchtop portable freezing container.[18]

Several independent studies have provided evidence that frozen embryos stored using slow-freezing techniques may in some ways be 'better' than fresh in IVF. The studies indicate that using frozen embryos and eggs rather than fresh embryos and eggs reduced the risk of stillbirth and premature delivery though the exact reasons are still being explored.

Researchers Greg Fahy and William F. Rall helped to introduce vitrification to reproductive cryopreservation in the mid-1980s.[19] As of 2000, researchers claim vitrification provides the benefits of cryopreservation without damage due to ice crystal formation.[20] The situation became more complex with the development of tissue engineering as both cells and biomaterials need to remain ice-free to preserve high cell viability and functions, integrity of constructs and structure of biomaterials. Vitrification of tissue engineered constructs was first reported by Lilia Kuleshova,[21] who also was the first scientist to achieve vitrification of oocytes, which resulted in live birth in 1999.[22] For clinical cryopreservation, vitrification usually requires the addition of cryoprotectants before cooling. Cryoprotectants are macromolecules added to the freezing medium to protect cells from the detrimental effects of intracellular ice crystal formation or from the solution effects, during the process of freezing and thawing. They permit a higher degree of cell survival during freezing, to lower the freezing point, to protect cell membrane from freeze-related injury. Cryoprotectants have high solubility, low toxicity at high concentrations, low molecular weight and the ability to interact with water via hydrogen bonding.

Instead of crystallizing, the syrupy solution becomes an amorphous iceit vitrifies. Rather than a phase change from liquid to solid by crystallization, the amorphous state is like a "solid liquid", and the transformation is over a small temperature range described as the "glass transition" temperature.

Vitrification of water is promoted by rapid cooling, and can be achieved without cryoprotectants by an extremely rapid decrease of temperature (megakelvins per second). The rate that is required to attain glassy state in pure water was considered to be impossible until 2005.[23]

Two conditions usually required to allow vitrification are an increase of the viscosity and a decrease of the freezing temperature. Many solutes do both, but larger molecules generally have a larger effect, particularly on viscosity. Rapid cooling also promotes vitrification.

For established methods of cryopreservation, the solute must penetrate the cell membrane in order to achieve increased viscosity and decrease freezing temperature inside the cell. Sugars do not readily permeate through the membrane. Those solutes that do, such as dimethyl sulfoxide, a common cryoprotectant, are often toxic in intense concentration. One of the difficult compromises of vitrifying cryopreservation concerns limiting the damage produced by the cryoprotectant itself due to cryoprotectant toxicity. Mixtures of cryoprotectants and the use of ice blockers have enabled the Twenty-First Century Medicine company to vitrify a rabbit kidney to 135C with their proprietary vitrification mixture. Upon rewarming, the kidney was transplanted successfully into a rabbit, with complete functionality and viability, able to sustain the rabbit indefinitely as the sole functioning kidney.[24]

Blood can be replaced with inert noble gases and/or metabolically vital gases like oxygen, so that organs can cool more quickly and less antifreeze is needed. Since regions of tissue are separated by gas, small expansions do not accumulate, thereby protecting against shattering.[25] A small company, Arigos Biomedical, "has already recovered pig hearts from the 120 degrees below zero",[26] although the definition of "recovered" is not clear. Pressures of 60 atm can help increase heat exchange rates.[27] Gaseous oxygen perfusion/persufflation can enhance organ preservation relative to static cold storage or hypothermic machine perfusion, since the lower viscosity of gases, may help reach more regions of preserved organs and deliver more oxygen per gram tissue.[28]

Generally, cryopreservation is easier for thin samples and suspended cells, because these can be cooled more quickly and so require lesser doses of toxic cryoprotectants. Therefore, cryopreservation of human livers and hearts for storage and transplant is still impractical.

Nevertheless, suitable combinations of cryoprotectants and regimes of cooling and rinsing during warming often allow the successful cryopreservation of biological materials, particularly cell suspensions or thin tissue samples. Examples include:

Additionally, efforts are underway to preserve humans cryogenically, known as cryonics. For such efforts either the brain within the head or the entire body may experience the above process. Cryonics is in a different category from the aforementioned examples, however: while countless cryopreserved cells, vaccines, tissue and other biological samples have been thawed and used successfully, this has not yet been the case at all for cryopreserved brains or bodies. At issue are the criteria for defining "success".

Proponents of cryonics claim that cryopreservation using present technology, particularly vitrification of the brain, may be sufficient to preserve people in an "information theoretic" sense so that they could be revived and made whole by hypothetical vastly advanced future technology.

Right now scientists are trying to see if transplanting cryopreserved human organs for transplantation is viable, if so this would be a major step forward for the possibility of reviving a cryopreserved human.[30]

Cryopreservation for embryos is used for embryo storage, e.g., when in vitro fertilization (IVF) has resulted in more embryos than is currently needed.

One pregnancy and resulting healthy birth has been reported from an embryo stored for 27 years after the successful pregnancy of an embryo from the same batch three years earlier.[31] Many studies have evaluated the children born from frozen embryos, or frosties. The result has been uniformly positive with no increase in birth defects or development abnormalities.[32] A study of more than 11,000 cryopreserved human embryos showed no significant effect of storage time on post-thaw survival for IVF or oocyte donation cycles, or for embryos frozen at the pronuclear or cleavage stages.[33] Additionally, the duration of storage did not have any significant effect on clinical pregnancy, miscarriage, implantation, or live birth rate, whether from IVF or oocyte donation cycles.[33] Rather, oocyte age, survival proportion, and number of transferred embryos are predictors of pregnancy outcome.[33]

Cryopreservation of ovarian tissue is of interest to women who want to preserve their reproductive function beyond the natural limit, or whose reproductive potential is threatened by cancer therapy,[34] for example in hematologic malignancies or breast cancer.[35] The procedure is to take a part of the ovary and perform slow freezing before storing it in liquid nitrogen whilst therapy is undertaken. Tissue can then be thawed and implanted near the fallopian, either orthotopic (on the natural location) or heterotopic (on the abdominal wall),[35] where it starts to produce new eggs, allowing normal conception to occur.[36] The ovarian tissue may also be transplanted into mice that are immunocompromised (SCID mice) to avoid graft rejection, and tissue can be harvested later when mature follicles have developed.[37]

Human oocyte cryopreservation is a new technology in which a woman's eggs (oocytes) are extracted, frozen and stored. Later, when she is ready to become pregnant, the eggs can be thawed, fertilized, and transferred to the uterus as embryos.Since 1999, when the birth of the first baby from an embryo derived from vitrified-warmed woman's eggs was reported by Kuleshova and co-workers in the journal of Human Reproduction,[21] this concept has been recognized and widespread. This breakthrough in achieving vitrification of a woman's oocytes made an important advance in our knowledge and practice of the IVF process, as the clinical pregnancy rate is four times higher after oocyte vitrification than after slow freezing.[38] Oocyte vitrification is vital for preserving fertility in young oncology patients and for individuals undergoing IVF who object, for either religious or ethical reasons, to the practice of freezing embryos.

Semen can be used successfully almost indefinitely after cryopreservation. The longest reported successful storage is 22 years.[39] It can be used for sperm donation where the recipient wants the treatment in a different time or place, or as a means of preserving fertility for men undergoing vasectomy or treatments that may compromise their fertility, such as chemotherapy, radiation therapy or surgery.

Cryopreservation of immature testicular tissue is a developing method to avail reproduction to young boys who need to have gonadotoxic therapy. Animal data are promising, since healthy offspring have been obtained after transplantation of frozen testicular cell suspensions or tissue pieces. However, none of the fertility restoration options from frozen tissue, i.e. cell suspension transplantation, tissue grafting and in vitro maturation (IVM) has proved efficient and safe in humans as yet.[40]

Cryopreservation of whole moss plants, especially Physcomitrella patens, has been developed by Ralf Reski and coworkers[41] and is performed at the International Moss Stock Center. This biobank collects, preserves, and distributes moss mutants and moss ecotypes.[42]

MSCs, when transfused immediately within a few hours post-thawing, may show reduced function or show decreased efficacy in treating diseases as compared to those MSCs which are in log phase of cell growth (fresh). As a result, cryopreserved MSCs should be brought back into log phase of cell growth in in vitro culture before these are administered for clinical trials or experimental therapies. Re-culturing of MSCs will help in recovering from the shock the cells get during freezing and thawing. Various clinical trials on MSCs have failed which used cryopreserved products immediately post-thaw as compared to those clinical trials which used fresh MSCs.[43]

Bacteria and fungi can be kept short-term (months to about a year, depending) refrigerated, however, cell division and metabolism is not completely arrested and thus is not an optimal option for long-term storage (years) or to preserve cultures genetically or phenotypically, as cell divisions can lead to mutations or sub-culturing can cause phenotypic changes. A preferred option, species-dependent, is cryopreservation. Nematode worms are the only multicellular eukaryotes that have been shown to survive cryopreservation.[44]Shatilovich AV, Tchesunov AV, Neretina TV, Grabarnik IP, Gubin SV, Vishnivetskaya TA, Onstott TC, Rivkina EM (May 2018). "Viable Nematodes from Late Pleistocene Permafrost of the Kolyma River Lowland". Doklady Biological Sciences: Proceedings of the Academy of Sciences of the USSR, Biological Sciences Sections. 480 (1): 100102. doi:10.1134/S0012496618030079. PMID30009350. S2CID49743808.

Fungi, notably zygomycetes, ascomycetes and higher basidiomycetes, regardless of sporulation, are able to be stored in liquid nitrogen or deep-frozen. Crypreservation is a hallmark method for fungi that do not sporulate (otherwise other preservation methods for spores can be used at lower costs and ease), sporulate but have delicate spores (large or freeze-dry sensitive), are pathogenic (dangerous to keep metabolically active fungus) or are to be used for genetic stocks (ideally to have identical composition as the original deposit). As with many other organisms, cryoprotectants like DMSO or glycerol (e.g. filamentous fungi 10% glycerol or yeast 20% glycerol) are used. Differences between choosing cryoprotectants are species (or class) dependent, but generally for fungi penetrating cryoprotectants like DMSO, glycerol or polyethylene glycol are most effective (other non-penetrating ones include sugars mannitol, sorbitol, dextran, etc.). Freeze-thaw repetition is not recommended as it can decrease viability. Back-up deep-freezers or liquid nitrogen storage sites are recommended. Multiple protocols for freezing are summarized below (each uses screw-cap polypropylene cryotubes):[45]

Many common culturable laboratory strains are deep-frozen to preserve genetically and phenotypically stable, long-term stocks.[46] Sub-culturing and prolonged refrigerated samples may lead to loss of plasmid(s) or mutations. Common final glycerol percentages are 15, 20 and 25. From a fresh culture plate, one single colony of interest is chosen and liquid culture is made. From the liquid culture, the medium is directly mixed with equal amount of glycerol; the colony should be checked for any defects like mutations. All antibiotics should be washed from the culture before long-term storage. Methods vary, but mixing can be done gently by inversion or rapidly by vortex and cooling can vary by either placing the cryotube directly at 50 to 95C, shock-freezing in liquid nitrogen or gradually cooling and then storing at 80C or cooler (liquid nitrogen or liquid nitrogen vapor). Recovery of bacteria can also vary, namely if beads are stored within the tube then the few beads can be used to plate or the frozen stock can be scraped with a loop and then plated, however, since only little stock is needed the entire tube should never be completely thawed and repeated freeze-thaw should be avoided. 100% recovery is not feasible regardless of methodology.[47][48][49]

The microscopic soil-dwelling nematode roundworms Panagrolaimus detritophagus and Plectus parvus are the only eukaryotic organisms that have been proven to be viable after long-term cryopreservation to date. In this case, the preservation was natural rather than artificial, due to permafrost.

Several animal species, including fish, amphibians and reptiles have been shown to tolerate freezing. These species include at least four species of frogs (Pseudacris crucifer, Hyla versicolor, Pseudacris triseriata, Lithobates sylvaticus) and several species of turtles (Terrapene carolina, hatchling Chrysemys picta), lizards, and snakes are freeze tolerant and have developed adaptations for surviving freezing. While some frogs hibernate underground or in water, body temperatures still drop to 5 to 7C, causing them to freeze. The Wood frog (Lithobates sylvaticus) can withstand repeated freezing, during which about 65% of its extracellular fluid is converted to ice.[46]

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Cryopreservation - Wikipedia

Corpse-freezing hasnt exactly gone mainstream, but most people are now familiar with the concept: you lay out a ton of cash, sign some papers, and spend a couple post-death decades in a cutting-edge meat locker, calmly awaiting the conditions for your eventual revival. Over 300 cold, dead Americansor dead, cold American brains, depending on which procedure they opted for (whole-body vs. brain-only)can currently be found in storage facilities across the country. All of them took a gambleone that was pretty cheap, metaphysically speaking: the worse case scenario here is just continued death.

For the time being, that is also the only scenario. Only time will tell whether these extremely dead optimists will once more, someday, get stuck in traffic, and/or roam an uncanny Singularity-scape with their AI-abetted computer brains. But we can at least start to guess whetheror ifthat day will ever come. For this weeks Giz Asks, we reached out to a number of neuroscientists, bioethicists, cryo advocates and skeptics to get some sense of what will happen to those frozen former consciousness-havers. Honestly its not looking good for them just yetbut the futures main business is to show up the pasts myopia/blinkeredness, so, who knows!

Biologist at the University of Liverpool and coordinator of the UK Cryonics and Cryopreservation Research Network

Id say that with todays technology, cryonics severely damages the bodys cells. Even under optimal conditions (i.e., the procedure starts right after death), there are several problems in cryonics. In particular, cryoprotectant agents have toxic effects on human tissues with prolonged exposure. Vitrifying large organs like the brain can also result in fractures due to different cooling rates in different parts. Under non-optimal conditions (i.e., if a significant time elapses between death and being cryopreserved) much more damage can occur because cells start to die, and brain cells in particular start to die within minutes after cardiac arrest, due to lack of nutrients and oxygen (called ischemia). Therefore, it will take huge scientific advances in areas like tissue engineering and regenerative medicine to make cryopreserved individuals alive and healthy again.

In addition, repair at the molecular level using nanotechnology will be necessary, yet this remains in the realm science fiction. That said, it is impossible to predict how technology will progress in the coming decades or centuries. As such, I would say that the chances of cryopreserved individuals ever be revived is low but not impossible. And then the argument is that the worse possible outcome of being cryopreserved is to remain dead, so cryonics gives you a chance of future revival that will not happen if you are buried or cremated.

Moreover, reversible and safe human cryopreservation would be a revolutionary technology in the field of critical-care. Patients with terminal diseases, including children, could opt to be placed on cryostasis until a cure were discovered. In a sense, we would have an alternative to death, which has profound philosophical, ethical and medical implications.

Co-Founder and CTO, X-Therma Inc., a company improving cold storage of stem cells, tissues, and whole organs

There are two different ways of cryogenically freezing people. One involves freezing just the brain or the headthe thinking here is that theres a smaller amount of tissue and you should preserve the essence of the person. Its also cheaper and easier. But storing the brains underlying structure, and the connections between cells, is likely much, much harder. The other method involves freezing the whole body, in the hopes that you could be revived one day when the right technology is available to fix your disease state and repair damage from the process.

There are a ton of barriers here, in both cases. The hardest thing to solve is: how do you freeze things without damaging them? You mix in all these cryoprotectantslike antifreeze for your car, but geared towards biologyin an effort to prevent ice formation within the cells and tissues. But you need to drastically lower the temperaturedown to about -196 degrees C, liquid nitrogen temperature. Preventing ice formation at that temperature, throughout a very large tissue, is very, very difficult. When the ice forms, its going to shear and cut the cells like a knifeits basically going to run a knife through the organs youre trying to preserve. And then theres desiccation: once you put those chemicals into an organ or a cell, it causes the water to leave the cells and dries them out, which damages cell to cell connections. Once those are damaged, repair becomes near impossible, since cells dont seem to rebuild those connections properly after being frozen. At least researchers see very little repair of the matrix.

So theres the chemistry problem (preventing ice), the biology problem (tissue damage, connection damage), the physics problem (how do you evenly cool something as large as an organ? And how do you warm it up evenly afterwards, without damaging it?).

I think there are much more imminent applications for cryopreservation, like organ preservation. Preserving organs has a high-value impact for the medical system, and also is much more feasible than preserving a whole body. You can save many, many lives with organ preservation.

Professor at the University of Oxford and Director at the Future of Humanity Institute and the Governance of AI program

Technically it seems like it should probably work. The freezing (rather: vitrification or plastination) and storing we can do now. The bringing back part may however require the assistance of machine superintelligence in order to repair the extensive cellular damage that occurs during the suspension process.

President, Cryonics Institute

The scientifically correct answer is that we do not know, since no one knows the future and what will be possible. However, that is why some people have signed up to preserve their bodies at liquid nitrogen temperatures in hopes that future technology and medicine will be able to answer that very question.

Just as it was impossible to raise the dead 100 years ago, they believe that new technologies like CPR and Cardiac defibrillation will change the definition of what it means to be dead. New technologies moving forward might mean advanced, AI-guided stem cell therapies that regenerate tissues that have been damaged by aging, freezing, or death itself. Ray Kurzweils law of accelerating returns suggests that technologically we are advancing at an exponential pace, and this means that things considered impossible even a few decades ago will become reality. For instance: the cell phone in your pocket that lets you communicate worldwide in real time while being able to access all of human knowledge at your fingertips. In the past such a device was called a crystal ball and was considered a myth. It seems likelybut only time will tell.

Researcher in 3D bioprinting and biofabrication at BioFab3D, St Vincents Hospital, Melbourne

All signs point to no. The freezing-down process is critical. Doing this in a way that preserves cell functionespecially regarding connectivity in the human brainis way beyond our current capabilities. Unfortunately, everyone who has ever been frozen so far is essentially turned to mush. These people will never be revived.

Cryonics in its current form is more of a religion than a science. Rather than a divine entity, its followers place their faith in technological progressbelieving that future advances will compensate for the terrible damage caused during current freezing techniques. There is no evidence or indication that this is possible. Though I dont doubt its prophets are well intentioned, contemporary cryonics is essentially a belief system providing comfort against the fear of death.

The ability of some organisms to survive freezing is a sign from nature that what cryonics promises might one day be possible. But getting there will require a massive investmentbillions of dollars, thousands of scientists, decades of research. Without a clear economic incentive, that investment is not forthcoming. As my old professor says, a vision without funding is hallucination.

Think that today it typically takes a couple of decades and a few hundred million dollars to develop one new medical treatment. The problems faced by cryonics are at least an order of magnitude more complex. By the time humanity solves them we might all be immortal anyway.

Director of Alcor Life Extension Foundation, the worlds leading cryonics organization

The short version is: many of the patients at Alcor will likely be revived sometime this century.

Had you asked a random person in 1940 if flight to the moon was possible, youd likely have been told no. If asked why, a typical answer was because theres no air to push against in space. This scientific-sounding but totally false objection was infamous among knowledgeable scientists, and was the basis for the New York Times 1920 editorial denouncing Robert Goddard. It was retracted on July 17th, 1969, one day after the launch of the Apollo 11 spaceflight.

Yet those knowledgeable about space flight had been forecasting flight to the moon for decades before the event. Similarly, those knowledgeable about nanomedicine have also been forecasting the revival of cryopreserved patients for decades, and those forecasts are likewise based on a sound assessment of physical law.

While we still hear skeptical sounding statements about cryonics, the obvious lack of any sound technical argument against the feasibility of cryonics is becoming increasingly obvious. Until the structures in the brain that encode our memories and personality have been so obliterated that they cannot in principle be inferred and restored to a functional state, you are not dead. This information theoretic criterion of death is obviously much more difficult to meet than current legal or medical definitions, hence the belief that cryopreserved patients are not actually dead.

Canada Research Chair in Neurobiology & Behaviour and Assistant Professor of Biology at McGill University and wrote The False Science of Cryogenics for the MIT Technology Review

If you mean people who have already had their brains, heads, or bodies cryogenically stored after death (or are doing so with current technology): no, they will never be revived. They are dead, and will remain dead forever. Will it ever be possible to store a dead person (or a dead persons brain) in such a way that they can be revived? Almost certainly not. Will it ever be possible to cryogenically suspend a living person for some period of time? Almost certainly. For how long? Impossible to say. Will it ever be possible to uploadtransfersomeones consciousness into a digital form? No. Consciousness is not a thing, its a bunch of different things that brains do. In theory, you could create a digital simulation that is a different thing from the person, and the person can still be either alive or dead. Either way, the new thing isnt them. A person is a particular physical causal system, not a computational abstraction.

Will it ever be possible to create a simulation or digital version of a dead person based on examination of their brain? This is not theoretically impossible, but it is so far outside our technology (both biological and computational) that anyone who says they know they answer of whether it will ever happen is probably selling something. The belief that a theoretically possible technologically will ever be practically possible and will come true if we want it bad enough is just quasi-religious wish fulfillment.

Look at the world. The only good thing we still reliably do for future generations is get out of their way. Lets not take that away from them toothey will have their hands full with all the horrific problems weve left them because of our selfishness and greed. We shouldnt making them responsible for keeping our bodies cold, too.

Professor, Chemistry, Warwick Medical School, whose team researches new cryoprotectants to help store biologics

The cryopreservation of cells underpins a huge range of fundamental and medical science; just like with food, we cannot leave cells lying around at room temperature and expect them to be fine to use, so low temperatures are essential to let us store (or bank) the cells.

Successful storage of cells requires careful addition and removal of cryoprotectants, as well as the precise control of freezing and thawing rates. In small volumes (for cells) this can be simple, but it becomes much harder as the volume increases and is one of (very) many problems of freezing a person. We must remember a human is a community of cells linked together, and those links need to be maintained for a tissue to be viable, especially for complex organs like the brain.

It is appealing to think that just because cells, or some tissues, are routinely cryopreserved that the same could be applied to an entire person, but this is really an over-simplification. No one can predict future technologies, but I dont see how this is possible, and claims that nanotechnology will put back together the damaged parts of the brain/body do not agree with scientific reality at the moment.

Reader in Bioethics, Newcastle University

First, I believe that any cryo-preserved corpse or brain that is already frozen (or will be in the near future) has zero chance because the individuals concerned are already dead and their death caused by fatal diseases currently incurable. Waking these corpses would involve so many major breakthroughs way beyond what is possible now, thawing complex tissue and organ systems into a viable state, applying regenerative technologies to make good the tissue damage, curing the fatal disease which killed them and finally reviving the dead person. Each of these is individually massively challenging and far beyond what is currently possible (and remember in most definitions death is an irreversible condition).

What is open as a possibility is if the cryo-person was not dead or terminally ill to begin withso this might involve combining cryo-preservation with euthanasia (thus compounding the moral problems, especially if the person was not terminally ill which is a requirement in most jurisdictions that allow euthanasia). I suppose this technique might be used to enable deep space exploration where the person was placed into a suspended animation though in this case cryo-preservation might not be the best thing because, using current technologies, the techniques are very damaging to cells though work is going on to improve the technique.

To touch on some of the wider social problemsif a person were cryo-preserved for several hundred years what would be their status in the future communityawoken alone with no friends or living relatives, like a ship-wreck survivor thrown up on some foreign shore.

Do you have a question for Giz Asks? Email us at tipbox@gizmodo.com.

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Will Cryogenically Frozen People Ever Be Revived?