Will suspended animation ever exist? It already does, if you count animals hibernating over winter. But if you mean the sort of suspended animation depicted in science fiction (where a person is placed in a pod and frozen so they can survive interstellar journeys), that's a little more fanciful.
But there are some very down-to-earth applications, assuming we can solve the problems with freezing human tissue.
For decades, we’ve known about the potential for using cold temperatures to slow the biological process and have recently started using it as a form of emergency, lifesaving treatment.
Officially termed ‘suspended animation for delayed resuscitation’, people suffering a heart attack, for example, can be quickly cooled to induce hypothermia. This slows their body’s processes and protects their organs, in particular their brains, while the blood flow is interrupted.
The technique dramatically reduces the risk of brain damage and is so effective that people can survive without medical treatment for up to 90 minutes.
This kind of suspended animation involves cooling the body to around 5°C (59°F), instead of its normal 37°C (98°F). Any lower and cells start to die.
As the temperature drops below freezing, the huge amount of water in our cells becomes dangerous. Water expands as it freezes and sharp ice crystals form, which puncture our soft cells and blood vessels.
Anyone who has experienced frostbite knows the destructive effect of cold on the body parts it affects. Freeze an entire person solid and you would kill them.
Yet we freeze human embryos (in one case for 19 years, before defrosting them and allowing them to grow into a healthy baby).
Embryos are frozen early, typically when they’re just a collection of a few cells, and they survive because they’re prepared first – a protective agent is added to suck out water and prevent ice crystals from forming.
Then the embryos are flash-frozen in tanks of liquid nitrogen at -196°C (-320°F), so they can be preserved in suspended animation.
The North American wood frog does something similar to get through the winter. As the temperature drops, the frog flushes its cells with glucose (nature’s antifreeze) and then allows itself to freeze until its heart stops and brain functions cease.
Ice surrounds its organs, but the glucose prevents damaging ice crystals from forming inside its tissues.
When temperatures rise, it slowly thaws out and carries on as normal. It would be a difficult feat for a human to pull off and would need some very risky water extraction and chemical injections into every part of our bodies.
Hibernation is a different approach. Small rodents, such as mice and hedgehogs, allow their body temperatures to drop to near-freezing, which causes a massive slowdown of their breathing and heart rates.
Bigger mammals don’t need to drop their body temperatures so much.
American black bears, for example, drop from 36°C to 30°C (96°F to 86°F). This reduces their metabolic rate by a quarter, which is enough to stop the bone and muscle loss that would normally occur from such long periods of inactivity.
There are good reasons why being frozen isn’t a great idea and for larger mammals like us, perhaps hibernation is a better option than suspended animation.
This article is an answer to the question (asked by Safia Hall, via email) 'Will suspended animation ever exist?'
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