Cryopreservation, often called Cryosleep or cryonics, aims to preserve patients with fatal diseases until future medical treatments can cure them. The idea originated in the mid-twentieth century as scientists began experimenting with freezing small organisms like fish and mammal embryos. Early trials freezing more complex organisms like hamsters were less successful due to freezing damage at the cellular level. By the 1960s, scientists developed techniques to slowly freeze or vitrify specimens without damaging cells through the formation of ice crystals. This paved the way for the modern cryopreservation of human patients.

The cryopreservation process

When a patient passes away, their body is frozen as quickly as possible, usually within minutes or hours of the time of death. The goal is to preserve the body before cell death and decay set in. The patient is first given an anticoagulant like heparin to prevent blood clots from forming. Warm fluids are then drained from the body and replaced with cold cryoprotectant chemicals like glycerol or DMSO. These chemicals help prevent ice crystal formation during freezing. The body is then cooled at a rate of 1-2°C per minute until it reaches temperatures below -130°C. At this ultra-low temperature, all biological processes grind to a halt as the body achieves a state of ultra-low temperature suspension. The frozen patient is stored in liquid nitrogen until future revived is attempted.

Cooling and thawing risks

Cryosleep aims to minimize ice crystal formation that can damage cells. However, there is still a risk of freezing or thawing injuries. Intracellular ice formation is theorized to mechanically destroy cell membranes and structures. Toxicity from cryoprotectants used during cooling and warming can also damage cells. The long period spent in deep freeze suspension poses significant biochemical risks as well. Water inside cells may form crystals leading to osmotic stress as it freezes. Unfolding of proteins and disruption of cell membranes are also theorized freezing damage mechanisms. Upon thawing, there are risks from the reverse processes like osmotic shock, recrystallization injuries and restoration of normal biochemical activity level after a long cryopreserved period poses challenges too.

Long-term storage challenges

Storing a frozen human body for decades or longer poses unique challenges compared to short term cryopreservation of sperm, embryos or cell lines. Liquid nitrogen tanks need to be continuously refilled to maintain temperatures far below freezing. There is a finite lifetime for storage dewars and facilities before equipment needs repairs or upgrades. There is also risk over long timescales from loss of liquid nitrogen through boil-off or accidental warming events causing temperature excursions. Securing enough funding for continued cryogenic storage and future revival attempts across decades is challenging and uncertain. Long delays to future medical advances create doubts over successful future restoration to healthy biological function after such extended cryopreservation. Exposure to radiation in the environment posing long term genetic and cellular damage risks. It remains unclear how long term suspended animation through Cryosleep can really be achieved or maintained safely without compromising viability.

Patient selection considerations

Not every deceased individual is an ideal cryopreservation candidate. Factors like cause of death, pre-existing conditions, age and body condition impact likelihood of successful future revival and restoration of normal function. Younger individuals with catastrophic injuries like trauma but limited pre-existing issues have better chances than elderly patients passing due to cancer, organ failures or frailty. Bodies should be preserved as soon as possible after death, ideally within hours to preserve cell viability before apoptosis and necrosis set in. Consent of next of kin is also required raising ethical issues for cryopatients unable or unwilling to consent themselves before demise. There are concerns future societies may feel no obligation to thaw or attempt to revive individuals from past eras with vastly different values, worldviews or medical knowledge.

The future of Cryosleep

While cryopreservation technology has advanced greatly, bringing patients back to healthy life after cryopreservation remains an immense scientific challenge. Experiments are ongoing to scale down cryoprotectant toxicities, improve handling of intracellular ice formation during freezing and leverage technologies like 3D tissue engineering for organ replacement therapy. Stem cell therapies may one day help regrow damaged tissues from cryopreserved individuals. Quantum levitation techniques are being explored to achieve freezing without any ice crystal formation to minimize mechanical intracellular damage.

Genetic engineering holds promise to heal injuries at genetic and epigenetic levels for patients cryopreserved before cellular or subcellular damage manifests. If such methods bear fruit, long term human cryopreservation with the potential for true suspended animation and future revival may become medically and technically feasible within decades. This would revolutionize medicine by offering immortality to those willing to embrace the promise and risks of cryosleep for future resurrection.

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