The Deep Freeze

Is freezing your body the stuff of nightmares, science fiction, or a future technology to aid long space travel? I’m not sure many people would have turned down an opportunity to take a cryogenic sleep through the last year, I certainly wish it had been an option. Let’s explore the science of cryogenics, where it is already used and whether could it be a future space technology.

Cryogenics is the study of what happens at VERY low temperatures, amongst other things, investigating how materials behave in these conditions. While some people have been frozen in the hope that one day science will be able to resurrect them (most notably, the rumour that Walt Disney was frozen), cryogenics isn’t all science fiction and forms of it are already used in a few industries. Certain food manufacturers use liquid nitrogen to cryogenically freeze produce, maintaining natural quality of the food, including taste. Overall, this can maximise production, minimise costs and keep food fresh for longer than its natural shelf-life. Physiotherapists use cyrotherapy, the application of ice to an injury, the oldest and most simple treatment which helps to control pain. However, modern methods have culminated in whole-body cryochambers which are more widely adopted among sport stars than your average citizen. Champions of this method state the short emersion sessions can “speed recovery, reduce injuries, increase energy and improve sleep“, whilst controlled scientific studies have more mixed results.

However, freezing food for preservation or cryogenic use in physiotherapy are still worlds away from the technology and understanding which would be required to freeze a human, and successfully awaken them. Thankfully, nature has achieved this before us and there are animals which may aid our cryogenic venture. The North American Wood Frog is a cryogenic marvel, allowing up to 65% of its body to completely freeze during the winter months. Externally, the frog appears completely frozen, as solid as a rock, but as the ice melts, the Wood Frog thaws, its heart restarts and off it hops. To see this incredible bit of nature, check out this short clip from A Perfect Planet, narrated by David Attenborough, where we meet the Wood Frog: https://www.bbc.co.uk/programmes/p091w1b3.

So, how does this little creature freeze without dying? Researchers at Carleton University in Ottawa (Canada) discovered the Wood Frog’s secrets. Usually, water is the main problem which faces freezing living species as our cells are at least 70% water. When a living species freezes, water is first to freeze and causes cell dehydration which damages organs. This means we cannot “reanimate” the frozen person/animal etc. as cells have died and organs are beyond repair. The Wood Frog however, has a safety mechanism in place to avoid all the water in its cells from freezing. As it begins to freeze, as with a human, the water in the Wood Frog freezes first. However, the Wood Frog’s liver reacts to the water freezing and creates an excess of glucose (the body’s natural sugar). When the system is flooded with glucose, the freezing temperature of the Wood Frog’s bodily water is lowered, meaning that even if temperatures drop below 0oC, they do not freeze. Therefore, while the Wood Frog appears frozen externally, on a cellular level, it never freezes. So, researchers have deduced how the frogs avoid cellular death, but they haven’t yet cracked the reanimation step: how does the Wood Frog restart its heart? If you want to learn more about the Wood Frog, check out this article in Discover magazine: https://www.discovermagazine.com/planet-earth/the-biology-of-cryogenics

We can also learn from other animals who greatly slow or halt their metabolic processes during hibernation, and manage to avoid muscle and bone wastage. We’re used to bears hibernating through winter months, but it was more recently discovered that a handful of primates also hibernate through colder months, or when food is scarce, without drastically dropping their body temperature. Researchers have investigated gray mouse lemurs and the role of microRNAs. Imagine an extension cord with multiple switches and lots of plugs. Each switch is a microRNA, able to switch a plug/device (representing genes or processes) “on” or “off” without changing the genetic code (i.e. the plugs are still plugged in even when the switch is off, so the genes/processes are there but not functioning). By using microRNAs, the gray mouse lemurs can control which biological processes need to remain “on” to protect the animal, and which can be switched “off” to conserve energy while they hibernate. This mechanism slows muscle wastage by preventing cell death and slowing/stopping unnecessary cell growth, switching from consuming sugars which require a lot of energy to break down, to slower burning fats.

While we may not yet have the technology to successfully freeze a human (known as cryonics or cryosleep), or currently understand the reanimation process, there is still discussion around the use of cryogenics in space travel to suspend animation or put travellers in a hibernation-like sleep. We’ve seen cryogenic examples in films such as 2001: A Space Odyssey, and more recently in the 2014 film, Interstellar. These may be works of science fiction, but NASA are researching such technology alongside the company SpaceWorks. Here, they envision “pods” which can induce deep-sleep states with “significantly reduced metabolic rates…over extended periods of time”, making longer space flight missions to Mars possible for humans.

More imminently though, researchers hope to use their research into cryogenics for improved organ preservation before transplantation. Professor Boris Rubinsky, from the University of California, removed a rat’s liver, filled it with glycerol (a similar sugar to glucose), froze the liver, thawed it before successfully transplanting it into another rat. While this worked for a rat’s liver, much research is still required before we can apply this to humans, but cryogenics could revolutionise organ transplantation.

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