How cryopreservation could end death as we know it

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It’s 2045. You just survived a car crash — but your heart didn’t. Decades ago, doctors would have been scrambling to find a donor heart while machines kept you alive. But now, thanks to advances in cryopreservation, they simply order a new heart from cold storage. Hours later, you’re recovering from surgery — your life extended by tech that didn’t exist when you were born.

Cryopreservation

This imagined future could soon be a reality.

Cryopreservation — the process of freezing and storing biological materials for later use — has already revolutionized healthcare. Millions of people have started families using cryopreserved sperm, eggs, and embryos, and frozen ovarian tissue is now used to restore fertility in women who’ve lost it due to chemo. Cryopreservation has also allowed us to bank donations of rare blood types for transfusions, bone marrow for cancer-fighting stem cell treatments, and skin allografts for treating severe burns.

But we may have only begun to tap into its potential. Some foresee cryopreservation helping us end the organ shortage, survive terminal illnesses, and maybe even populate the solar system.

Where we’ve been

The journey to such a sci-fi future started with one of the most valuable substances on Earth: bull semen. In the 1930s, farmers in the United States, Russia, and other parts of the world were using artificial insemination for breeding livestock. It not only had a better conception rate than natural reproduction, but also reduced the amount of semen needed for a pregnancy, meaning one high-quality male could impregnate more females.

One of the biggest challenges the farmers faced, though, was getting the sperm into the females quickly enough. Mixing semen with an egg yolk-based “extender medium” and then cooling it to about 41 degrees Fahrenheit extended its viability. But farmers still had just a few days between when they collected it and when it expired. Attempts to freeze, store, and then thaw the semen failed because ice crystals would form outside the sperm cells, causing damage that prevented conception.

A breakthrough came in 1949 when English biologist Christopher Polge discovered that he could produce healthy chicks from frozen and thawed chicken semen if he mixed glycerol with the extender medium. The compound acted as a “cryoprotectant,” protecting the sperm cells from damage during freezing. He soon refined the technique to work with bull semen, too.

“Time has lost its significance,” Alan Sterling Parkes, one of Polge’s collaborators, told The New York Times in 1951. “The vitality and fertility of the sperm will be retained for an indefinite period. An animal could be used as a sire long after its death. What is true of animals is also true of men.”

It wasn’t true of men right away — human sperm were still nonfunctional after thawing, even when frozen with glycerol. Soon after Polge’s team’s breakthrough, however, American biologist Jerome Sherman started conducting his own cryopreservation experiments with human semen. He discovered the key to effectively cryopreserving it was to first use a centrifuge to concentrate the sperm. After mixing the cells with a mixture of glycerol and extender medium, he then had to freeze them slowly before storing them on dry ice. 

In 1953, the first three human babies conceived using cryopreserved sperm were born. Before the end of the 20th century, researchers would discover the right combinations of techniques, protectants, and refrigerants to successfully cryopreserve human eggs, embryos, blood cells, skin allografts, and more.

“In the future, they might find a cure for my cancer and wake me up.”

JS, a teen with terminal cancer

These developments inspired scientists and science-fiction writers alike to imagine a radical future use for the technology: freezing and storing whole people. The theory was that a person could be cryopreserved after death and then revived whenever a cure for what killed them was finally available — years, decades, or even centuries later. In 1967, psychology professor James Bedford became the first person to have their corpse cryogenically frozen. Since then, an estimated 500 people have done the same.

“I want to live and live longer, and I think that, in the future, they might find a cure for my cancer and wake me up,” JS, a teenager whose body was cryogenically frozen following her death in 2016, wrote in a letter to a high court. “I want to have this chance.”

Where we’re going (maybe)

While the cryopreservation of cells and tissues is now routine in healthcare, the freezing and storing of whole human bodies shortly after death, also known as “cryonics,” is still rare and controversial. Some question the morality of trying to “cheat death” with cryopreservation, while others argue that those selling the service are taking advantage of people who are sick or simply scared of dying. Some cryonics companies charge $200,000 or more per body.

Even if future doctors could treat the cause of death in people who have been cryopreserved, there’s a good chance that the bodies would be too damaged to be revived. You need to use the right cryoprotectants and the right techniques for freezing and thawing. The bodies that have been thawed and examined to date have shown signs of cracking and other damage, which certainly doesn’t inspire confidence. 

Past failures don’t, however, mean we’ll never be able to figure out the right way to cryopreserve humans. And we could still achieve breakthroughs that are as impactful on healthcare as the freezing of embryos and stem cells. “Cryobiology is an engineering problem,” João Pedro de Magalhães, head of the Genomics of Ageing and Rejuvenation Lab at the University of Birmingham and co-founder of biotech startup Oxford Cryotechnology, told Freethink. “We understand the biology — we just need to engineer the solutions to overcome the challenges and limitations we still have in preserving biological materials.”

One of the biggest challenges: size. It’s much easier to freeze and evenly thaw something small, like an embryo comprising just 100 or so cells, than it is to do the same with larger biological materials, like organs or whole bodies. The center of the object can take longer to freeze than the outer layers, and vice versa during warming. Outer layers thaw faster than the core layers. The uneven temperatures can encourage ice formation and lead to cracking, tearing, and other tissue damage. “The problems get worse the bigger the tissue samples get,” Ariel Zeleznikow-Johnston, a neuroscientist at Monash University, told Bloomberg in 2024. “You get these big differences in temperature gradients. People have tried to get around this with cryoprotectants, but they are toxic in and of themselves.”

In July 2023, scientists at the University of Minnesota announced a breakthrough in combating this issue. For a study published in Nature Communications, they mixed iron oxide nanoparticles into a cryoprotectant solution before running it through the blood vessels of rat kidneys. Then they used liquid nitrogen to flash-freeze the organs. This approach, called “vitrification,” causes cells to take on a glass-like state and is widely used in embryo cryopreservation today because it leads to less damage. 

Study co-first author Zonghu Han manipulating one of UMN’s rat kidneys.

After storing the kidneys for up to 100 days, the University of Minnesota team placed the vitrified organs inside a copper coil and ran a current through it. This created a magnetic field that caused the iron nanoparticles in the kidneys to heat up, which warmed them evenly in about 90 seconds.

The scientists then flushed the iron-containing cryoprotectant from the kidneys and transplanted them into five rats. Though organs weren’t fully functional at first, in one month post-surgery, they were indistinguishable from kidneys that had been transplanted without prior freezing.

As John Bischof, the study’s co-senior author, put it in a news release, “This is the first time anyone has published a robust protocol for long-term storage, rewarming, and successful transplantation of a functional preserved organ in an animal.” 

“If we could cryopreserve human organs … we could save thousands of lives per year.”

João Pedro de Magalhães

Rat kidneys aren’t exactly huge — they typically weigh less than 1 gram. But they contain tens of millions of cells of at least 20 different types, making them way bigger and more complex than something like an embryo. That someone was able to successfully freeze, thaw, and transplant any mammalian organ, regardless of size, marks a major milestone along the path to what many see as the next big goal of cryopreservation: human organ banking.

Donor organs do not last long outside the body. Surgeons have somewhere between six and 36 hours after removal, depending on the organ, to transplant them into a recipient. And even within that window, a longer delay can mean a worse transplant outcome.

If we could cryopreserve donor organs, we could potentially improve transplant outcomes — organs could be stored for days, weeks, or even years before use if needed. We could also increase the supply of donor organs, which currently falls short of the demand. Every year, thousands of donated organs are discarded in the U.S. because doctors turn them down. The time the organ has been out of a body is one of the factors they consider when making this decision. “If we could cryopreserve human organs, we could develop organ banking for transplants that would save thousands of lives per year,” ​​said Magalhães. “It would be a major medical breakthrough.”

The University of Minnesota team is already working to scale its technique to larger organs, though it isn’t ready to publish anything on those studies. Magalhães, meanwhile, is optimistic that an even greater milestone in cryopreservation is now within reach. “I think in the next 10 years we will see cryopreservation … and [the] revival of small rodents,” he said, noting that this could lead to an increase in funding for cryobiology, which is currently a small field.

This funding could go farther today than at any time in the past. Scientists could use the data generated by any new experiments to train artificial intelligence that could help us solve existing challenges in cryopreservation. Oxford Cryotechnology is already developing AI models to help identify new cryoprotectants, and Magalhães said that’s just one potential application: “In addition to new cryoprotectants, AI can help in many other ways, for instance, optimizing concentrations and temperature gradients for cryopreservation of different cell types and tissues.”

Yet AI is only as good as its training data, and because cryobiology is such a small field, there isn’t a ton of high-quality data. Hence the need for more funding to generate it. It’s possible that Cradle Health will be the group to achieve the whole-rodent breakthrough that Magalhães thinks will inspire this funding. The startup, which was founded by biotech prodigy Laura Deming and has raised $48 million in investment, announced in June 2024 that it had vitrified and rewarmed slices of rodent brain tissue in a way that allowed the tissue to retain some of its electrical activity after thawing. That’s a first in the field of cryopreservation.

Cradle hopes to figure out how to cryopreserve human organs before moving on to whole rodents. But its long-term goal is to freeze humans, specifically ones who are sick with terminal illnesses, so that they could “hibernate” until a cure is found. “Think the hibernation pods you see in space movies for long-term travel,” Deming wrote on X. “We want to build that.”

If Cradle — or any other group — is able to cryopreserve and revive humans, it’s possible the tech would eventually be applied to space travel. A trip to a planet like Jupiter is likely to take years, and being able to “cryosleep” through journeys to deep space could protect astronauts’ mental health and eliminate the need to pack food for the trip, saving payload space and cutting costs.

It may take decades to get there, but if cryopreservation is, as Magalhães said, largely an engineering problem, we can keep chipping away at it using the latest available technologies. With each breakthrough, we’ll move closer to a future where we end the organ shortage, reinvent end-of-life care, and populate the solar system. And maybe even stop death itself.

Updated, 09/12/25 1:15 pm ET: This article was updated with a new introduction. Other minor edits were made throughout for length and clarity.

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