The Quest for Reversible Cryopreservation

Much of the talk of low-temperature preservation of tissue here at Fight Aging! directly relates to the cryonics industry: the work of preserving the brains of those who age to death prior to the advent of rejuvenation biotechnology, so that they have some possible chance at a longer life in the future. There is a large mainstream cryobiology industry and research community that shares essentially the same goals when it comes to organs and tissues, although cryobiologists have historically been quite hostile towards cryonics groups. It's the same old story of the conformist mainstream pushing away anyone who is doing something out of the ordinary - yet all bold new technologies and approaches start exactly that way, with a small group moving the boundaries of the possible and the plausible.

In any case, back to the commonalities: both cryobiologists and cryonicists want to produce the means for reversible cryopreservation rather than the presently irreversible methods of vitrification used on the human patients stored at Alcor, the Cryonics Institute, KrioRus, and so forth. Presently irreversible is not forever irreversible, of course, but the cryoprotectant compounds used now are pretty toxic, which adds an additional level of difficulty to the task of restoring patients to life. A reasonable argument is that given that this task requires technologies such as swarms of medical nanorobots, and sufficient control over small-scale biology to be able to repair arrangements of macromolecules within cells, then sequestering toxic molecules along the way shouldn't be a big deal by comparison.

So the cryobiologists want to be able to store organs and other large tissue masses in the same way that we can presently store embryos - in the deep freeze, so that donated organs or organs grown to order can be stored until needed. The cryonics community includes some groups with expertise in this area, such as 21st Century Medicine, and the development of reversible cryopreservation would be one of the potential spin-off technologies that could draw greater funding and interest into cryonics.

Here is an article on the present state of work on cryopreservation not directly related to the cryonics industry:

For most animals on the planet, prolonged exposure to temperatures below freezing means death. But for the wood frog (Rana sylvatica), and for an unlikely collection of other organisms ranging from insects to plants to fish, surviving the cold is a routine part of life. The Alaskan Upis beetle survives at -60°C in the wild and down to -100°C in a laboratory. Species of Arctic fish swim fluidly through -2°C water, and snow fleas hop atop snow banks at -7°C. These animals all have tricks either to survive freezing, called freeze tolerance, or to lower their internal freezing temperature so they don't freeze at all, called freeze avoidance.

However, cooling a tissue that is not adapted to tolerate or avoid freezing - as cryobiologists seek to do with human organs - is a whole different ball game. One can expect irreversible and widespread damage from the formation of ice crystals at temperatures below 0°C: cells shrivel and collapse, extracellular matrices rip apart, blood vessels disintegrate.

But researchers aren't giving up. Organ cryopreservation, if possible, would transform medicine the way refrigeration transformed the food industry. Currently, human organs harvested for transplant are not frozen - they are kept in cold storage, which prevents deterioration for a few hours at the most. Human hearts, for example, can be preserved for only 4 to 5 hours. But if scientists could learn the tricks of the trade from nature, and add days, weeks, or even years to the lifetime of an organ, hospitals could bank frozen organs for transplant as needed.

Over the last 70 years, the technique for freezing human sperm and embryos, a mainstay of fertility clinics, has not differed much from how frogs freeze in Ohio- add a glut of glycerol and lower the temperature slowly. But today, clinics and hospitals are turning to a technique that no known organism experiences in nature - transforming tissues to glass.

Vitrification is the rapid cooling of a substance to a glass state, achieved by pumping enough cryoprotectants into cells or tissues, and cooling them fast enough, so that they transform into an ice-free glass. Through vitrification, scientists have successfully completed two of the most complex examples of cryopreservation to date: a 40,000-cell fly embryo and a rabbit kidney.

Though it won't be easy, many believe that organ cryopreservation should be possible. Indeed, thanks to chemical cryoprotectants and sophisticated freezers, scientists and companies already have techniques to freeze sperm, eggs, embryos, and pools of cells such as blood or stem cells. And in the last decade, successful preservation of some solid tissues has offered hope that the long-neglected field is not dead in the water.

In 2005, heart surgeons in Israel used an antifreeze protein from fish to preserve rat hearts at −1.3°C for 21 hours, then successfully transplanted them into recipient rats, where the hearts pumped away for 24 hours prior to dissection for analysis. In 2003, [21st Century Medicine], a California company similarly preserved a rabbit kidney at below-freezing temperatures and then thawed and transplanted it into a recipient rabbit, which remained healthy with that kidney alone for more than a month. And since 2000, researchers at the US Department of Agriculture have been cryopreserving the embryos of tropical flies for years at a time, then thawing them with ease and watching them hatch and live normal lives.

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