In 1949, an English biologist named Christopher Polge made a discovery that would change medicine forever. He was using liquid nitrogen to freeze various biological samples and study their structure under the microscope. It was known that sufficiently cold temperatures would stop all of the biochemical processes within a cell, preserving it in the state in which it was frozen. Unfortunately, the resulting formation of ice crystals would also cause fatal damage – most living cells and tissues could not survive the freezing and thawing processes.
Alongside these experiments, Polge was also studying the motion of rooster sperm. He would use glycerol to add viscosity to some of the sperm samples, then study how they moved. One day, Polge mixed up his samples, accidentally freezing one of the sperm samples in liquid nitrogen. Yet after the sample was thawed, he was surprised to find that the sperm were still moving. Further experiments soon confirmed that the glycerol had protected the sperm against damage by reducing the formation of ice crystals. The next year, he produced the first chicks from eggs fertilised with frozen sperm. Polge had discovered what we now know as a cryoprotective agent.
Cryopreservation is the preservation of biological material using very low temperatures while causing as little damage to the material as possible. Cryopreservation quickly saw applications in fertility medicine, allowing human sperm, oocytes and later embryos to be preserved. Today, cryopreservation has broader uses, including in the transportation and storage of stem cells and the genetic materials used in gene therapies. However, even before Christopher Polge’s discovery, scientists were dreaming of a far more ambitious application for cryopreservation: the preservation of deceased humans for future revival, also known as cryonics.
While in hospital in 1947 recovering from wounds sustained during World War II, American academic Robert Ettinger learnt of new work being done in the field of cryopreservation. Ettinger was already interested in cryopreservation and its implications for medicine at this time. His view was that the definition of death was relative, and dependant on available medical technology: a stopped heart meant death in a remote village in the Amazon, but not in the emergency department of a hospital. He realised that cryopreservation could be used as a form of ‘medical time travel’, allowing a dead patient to be preserved until a time at which medicine was sufficiently advanced to ‘cure’ them.
Over the following decade, Ettinger continued to follow advances in cryopreservation while developing his ideas. While cryopreservation of single cells may have become a reality, preserving tissues, let alone an entire human, was a whole different kettle of fish – for reasons we’ll discuss later. Yet Ettinger remained optimistic. By that same philosophy of ‘medical time travel’, it didn’t matter if freezing damage would be fatal by today’s standards, so long as future medicine had the means to reverse it. In his view, this would require relatively little scientific progress. And so in 1960, Ettinger wrote to around 200 intellectually, financially and socially distinguished Americans, summarising the case for human cryopreservation.
The response was underwhelming. It was clear that there was a significant cultural bias against the idea of evading death. To Ettinger’s disappointment, many people were reluctant to even admit that illness and death were bad things. People needed more exposure to these ideas for cryopreservation to pass from science fiction into the scientific mainstream. In 1964, Ettinger published ‘The Prospect of Immortality’, a book in which he argued that the prospect of bringing people back to life with medical technology should be taken seriously. The book was a success, with Ettinger becoming an overnight media celebrity, appearing on television and radio to promote human cryopreservation. The idea that freezing recently deceased humans could be a worthwhile pursuit had finally achieved widespread attention. Unfortunately, navigating the real life practicalities of cryopreservation would not be plain sailing.
The idea of human cryopreservation was ridiculed by many, and still is to this day to a lesser extent. The central issue, at least where scientific plausibility was concerned, was the extent of the damage that would be sustained by the bodies during the freezing process. As the field of cryopreservation advanced, it was found that the rate at which cells are cooled is important. Freeze a cell too quickly and ice crystals would destroy it. Freezing too slowly, however, would cause cells to shrink and die as water was drawn out of them. Over time, scientists discovered that different cell types had different optimal freezing rates, allowing for more effective cryopreservation. Yet in the case of entire organs, which contain many different cell types, this seemed to be an insurmountable problem. In addition, many of the cryoprotective agents that would need to be used to limit ice damage were themselves quite toxic – yet another problem that the medicine of the future would need to deal with.
Undeterred, the first human cryopreservation companies were established, and in the late 1960s small freezing operations began. This was completely uncharted territory, and so it’s perhaps unsurprising that many of these early cryopreservation cases were chaotic affairs. Some corpses slowly thawed on beds of dry ice, while cryonicists played a macabre jigsaw puzzle trying to fit four bodies into one liquid nitrogen capsule. In other cases the capsules failed, causing bodies to thaw and begin to decay before anyone noticed, while other bodies were thawed when their families stopped paying the running costs. Some bodies even ‘cracked’ after being frozen too quickly.
Since these failures, both the science and logistics of cryopreservation have improved considerably, and most people frozen today can expect to remain frozen. As of the time of writing (September 2022), around 500 people have been cryopreserved, including Robert Ettinger, and another 1500 are signed up. However, the early days were gruesome, and half a century on, only a single person frozen before 1974 – James Bedford – is still preserved. Why? His family took custody of his capsule and cared for it at their own expense.
Today the core principles of cryopreservation are unchanged. The goal of cryopreservation is to halt biochemical processes within the body as soon after death as possible, preventing any decay from occurring. However, the methods for doing so have been refined and cryopreservation companies have become much more professional. The science, too, has advanced with the development of better cryoprotectants. More recently, attention had been turning towards a form of cryoprotection that could be a significant leap forward for the field: vitrification.
In vitrification, special cryoprotective agents are used to make water solidify ‘like glass’: instead of forming ice crystals, water molecules are immobilised in their amorphous liquid state. This not only avoids ice damage completely, but also avoids the need for optimal cooling rates, circumventing the issue mentioned earlier, where organs contain many cell types that need to be cooled at different speeds. The biggest problem with vitrification is that the cryoprotectants used are quite toxic, and vitrification has not yet been successfully reversed in human organs. Once again, ‘medical time travel’ could provide a solution to this problem. What’s more, developing reversible vitrification methods is of interest to more than just the currently niche field of human cryopreservation. Reversible vitrification would transform organ transplantation, allowing whole organs to be preserved for far longer periods than is currently possible and greatly improving organ availability.
Despite these advances, there remain many sceptics, and the medical community is generally not supportive of human cryopreservation. Enthusiasts remain adamant that we should be freezing people now and worrying about thawing later, since medicine will surely be able to restore them in the future. Opponents argue that cryonicists underestimate how difficult it will be to repair the damage caused by cryopreservation. Will they be proven right, or will Robert Ettinger one day walk the Earth again? Only time will tell.
Short history of Cryonics and CI: https://www.cryonics.org/ci-landing/history-timeline
Life suspended: The past and future of cryopreservation: https://www.me.washington.edu/news/article/2020-09-01/life-suspended-past-and-future-cryopreservation
Suspension Failures: Lessons from the Early Years: https://www.alcor.org/library/suspension-failures-lessons-from-the-early-years/
Principles of cryopreservation by vitrification: https://pubmed.ncbi.nlm.nih.gov/25428002/
Why Cryonics Makes Sense: https://waitbutwhy.com/2016/03/cryonics.html
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