Cryonic suspension

Cryonics (from Greek κρύος kryos meaning 'cold') is the low-temperature freezing (usually at −196 °C or −320.8 °F or 77.1 K) and storage of a human corpse or severed head, with the speculative hope that resurrection may be possible in the future. Cryonics is a regarded with skepticism within the mainstream scientific community. It is a pseudoscience, and its practice is quackery. Cryonics (from Greek κρύος kryos meaning 'cold') is the low-temperature freezing (usually at −196 °C or −320.8 °F or 77.1 K) and storage of a human corpse or severed head, with the speculative hope that resurrection may be possible in the future. Cryonics is a regarded with skepticism within the mainstream scientific community. It is a pseudoscience, and its practice is quackery. Cryonics procedures can begin only after clinical death, and cryonics 'patients' are legally dead. Cryonics procedures ideally begin within minutes of death, and use cryoprotectants to prevent ice formation during cryopreservation. It is however not possible for a corpse to be reanimated after undergoing vitrification, which causes damage to the brain including its neural networks. The first corpse to be frozen was that of Dr. James Bedford in 1967. As of 2014, about 250 bodies were cryopreserved in the United States, and 1,500 people had made arrangements for cryopreservation after their legal death. Cryonicists argue that as long as brain structure remains intact, there is no fundamental barrier, given our current understanding of physical law, to recovering its information content. Cryonics proponents go further than the mainstream consensus in saying that the brain does not have to be continuously active to survive or retain memory. Cryonics controversially states that a human survives even within an inactive brain that has been badly damaged, provided that original encoding of memory and personality can, in theory, be adequately inferred and reconstituted from what structure remains. The cryonics argument that death does not occur as long as brain structure remains intact and the information is theoretically readable has received some mainstream medical discussion in the context of the ethical concept of brain death and organ donation. Cryonics uses temperatures below −130 °C, called cryopreservation, in an attempt to preserve enough brain information to permit future revival of the cryopreserved person. Cryopreservation may be accomplished by freezing, freezing with cryoprotectant to reduce ice damage, or by vitrification to avoid ice damage. Even using the best methods, cryopreservation of whole bodies or brains is very damaging and irreversible with current technology. Cryonics requires unknown future technology to repair or regenerate tissue that is diseased, damaged, or missing. Brain repairs in particular will require analysis at the molecular level. This far-future technology is usually assumed to be nanomedicine based on molecular nanotechnology. Biological repair methods or mind uploading have also been proposed. In conventional cryobiology practice, long-term preservation of biological tissue can be achieved by cooling to temperatures below −130 °C (−202 °F; 143 K). Immersion in liquid nitrogen at a temperature of −196 °C (−320.8 °F; 77.1 K) is often used for convenience. Water that freezes during cryopreservation is usually water outside cells, not water inside cells - so, rather than bursting during freezing, cells instead become dehydrated and compressed between ice crystals that surround them. Intracellular ice formation occurs only if the rate of freezing is faster than the rate of osmotic loss of water to the extracellular space. When used at high concentrations, cryoprotectants can stop ice formation completely. Cooling and solidification without crystal formation is called vitrification. The first cryoprotectant solutions able to vitrify at very slow cooling rates while still being compatible with whole organ survival were developed in the late 1990s by cryobiologists Gregory Fahy and Brian Wowk for the purpose of banking transplantable organs. This has allowed animal brains to be vitrified, warmed back up, and examined for ice damage using light and electron microscopy. No ice crystal damage was found; cellular damage was due to dehydration and toxicity of the cryoprotectant solutions.