Cryopreservation
[1] At low temperatures (typically −80 °C (−112 °F) or −196 °C (−321 °F) using liquid nitrogen) any cell metabolism which might cause damage to the biological material in question is effectively stopped.
Molecules, referred to as cryoprotective agents (CPAs), are added to reduce the osmotic shock and physical stresses cells undergo in the freezing process.
[2] Some cryoprotective agents used in research are inspired by plants and animals in nature that have unique cold tolerance to survive harsh winters, including: trees,[3][4] wood frogs,[5] and tardigrades.
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.
[8] Snapping turtles Chelydra serpentina and wall lizards Podarcis muralis also survive nominal freezing but it has not been established to be adaptive for overwintering.
[10][11] 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.
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.
Such machines are used for freezing oocytes, skin, blood products, embryos, sperm, stem cells, and general tissue preservation in hospitals, veterinary practices and research laboratories around the world.
[33] 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.
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.
[41] 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.
Tissue can then be thawed and implanted near the fallopian, either orthotopic (on the natural location) or heterotopic (on the abdominal wall),[43] where it starts to produce new eggs, allowing normal conception to occur.
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,[25] this concept has been recognized and widespread.
[46] 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.
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.
As a result, cryopreserved MSCs should be brought back into the log phase of cell growth in in vitro culture before these are administered for clinical trials or experimental therapies.
[53] 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.
Cryopreservation 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 an identical composition as the original deposit).
Multiple protocols for freezing are summarized below (each uses screw-cap polypropylene cryotubes):[56] Many common culturable laboratory strains are deep-frozen to preserve genetically and phenotypically stable, long-term stocks.
[57] Based on a speculative science, cryonics is controversial in scientific debate and can be better understood as an emergent death ritual along the social evolution of human culture and technology.
[citation needed] Belief in an afterlife, or second life, where the phenomenological body endures a transition or resurrection is recurrent across ancient tradition, religion and science fiction.
However, the increasingly socialised language of cryotechnology in health and wellness treatments, recontextualises waking of the un/dead into the biosocial sphere, framing mortality as something akin to illness which can be controlled or cured.
Ability to access and harness forms of cryotechnology (from cryostorage of food, blood or sperm) is historically bound to class, wealth and power.
It is central to fertility, health and death and in this sense, cryonics is a mechanism in the ‘cold chain’ [61] power structure with potential to produce, preserve, and/or restrict life.
This modern form of biopower is integrated into society as a new method of dictating power over the individual or phenomenological body when determining life or death outcomes.
Considering the cyclical nature of wealth and power in society already (systemically undercut by race, gender, class, and religion), it is likely that the use of cryonics in the future will have a self-perpetuating influence on these structures.
Hence, there is further potential to amplify already existing power imbalances as implications from a legal, financial, and socio-cultural perspective will contribute to sustaining the cryonic practice, excluding most members of society in order to benefit an already dominant group.
Ultimately, cryonics reinforces hegemonic inequalities already existing in society today in which few will benefit and calls into question the ethical ambiguity of individual bodily autonomy in the pursuit of self-preservation or survival.
Those seeking to expand their lifespan in spite of death through preservation suffer from chronic, incurable, and/or degenerative conditions, having to overcome numerous legalities regarding body disposal, human tissue storage, the rights of minors, and in some cases medically assisted suicide.
