Preservation injury

Long-term cryopreservation requires cooling to near −196 °C (−321 °F), the boiling point of liquid nitrogen. Cooling whole people to this temperature causes injuries that are not reversible with present technology. The common belief that water freezes inside cells causing them to burst is a myth,but damage from freezing can still be serious. When untreated tissue is slowly cooled below the freezing point of water, ice forms between cells, causing mechanical and chemical damage. Cryonics uses cryoprotectants to reduce this damage. Cryoprotectant solutions are circulated through blood vessels to remove and replace water inside cells with chemicals that prevent freezing. This can reduce damage greatly, but not enough for whole people to recover spontaneously from cryopreservation. When used at high concentrations, cryoprotectants stop ice formation completely. Cooling and solidification without freezing is called vitrification. The first cryoprotectant solutions able to vitrify at very slow cooling rates while still being compatible with tissue survival were developed in the late 1990s by cryobiologists Gregory Fahy and Brian Wowk for the purpose of banking transplantable organs.These solutions were adopted for use in cryonics by the Alcor Life Extension Foundation, for which they are believed to permit vitrification of some parts of the human body, especially the brain. 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.. The Cryonics Institute also uses a vitrification solution developed by their staff cryobiologist, Dr. Yuri Pichugin, applying it principally to the brain..Vitrification in cryonics is different than vitrification in mainstream cryobiology because vitrification in cryonics is not reversible with current technology. It is only structural vitrification. When successful it can prevent freezing injury in some body parts, but at the price of toxicity caused by cryoprotectant chemicals. The nature of this toxicity is still poorly understood. Cryonicists assume that toxicity is more subtle and repairable than obvious structural damage that would otherwise be caused by freezing. If, for example, toxicity is due to denatured proteins, those proteins could be repaired or replaced.