Cryopreservation in humans happens after they die as they have requested to be preserved in this way before they passed away. As soon as a person who wishes to be cryopreserved will have their body sent off to be frozen soon after their death. Cryopreservation is the process in which the body is frozen at a very low temperature of about -196°C with the hopes of thawing out that person in the future so that they can live again.
A person can only be cryopreserved when they are declared “legally dead”. This means that the cryopreservation process can only begin once the organs within the body are no longer functioning. When the process begins, the now dead person is put into an “ice slurry” where the body can be cooled down at a faster rate. Chemicals are then injected into the body to ensure that the brain doesn’t become damaged and the blood does not clot after death. Blood is removed from the body as it reached just above the freezing point for water, as this allows for chemicals to be put into the body which will help keep it preserved.
The chemicals that replace the blood in the body make sure that ice crystals don’t form in the body once it has been immersed in the liquid nitrogen. If ice crystals form in the body, this will damage the cells. When the chemicals that ensure that ice crystals don’t form in the body are put in, the blood vessels are flushed out just before this process. After the body is full of the chemicals that makes sure there will be no ice crystals, the body is then put immersed into the liquid nitrogen, where it will become colder until it freezes completely at about -196°C. After that, the body will stay there until it is thawed in the future and the body can be revived.
When a person alive decides they would like to be cryopreserved, it is advised that they notify the company who will be preserving them after death of any terminal illnesses. This is because the company can then plan in the event of the death, as they will need to act fast in order to preserve the cells in the body as best as they can. Scientists expect full revival possible and the body to return back to how it was alive possible in the future with hard work and research.