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What Exactly Is “Suspended Animation”?

Learn about suspended animation and discover what science fiction doesn’t tell you.

No matter how hard things get, life goes on, unless you are in suspended animation. But don’t worry, this doesn’t mean you’re dead - just paused. Maybe comparing it with sleep wouldn’t be so wrong, or rather a narcosis?

The concept of suspended animation is a prominent feature in sci-fi stories, but oftentimes little explanation of how it even works is given. Compared to reality, it’s often wrongly depicted. Generally speaking, it’s the unconscious state of an organism with very low metabolic activity. But we want to be a little more specific than that.

In this article we go over what exactly suspended animation is, why it isn’t exactly the same as cryopreservation, and how we can use it to our advantage.

a stopwatch frozen inside an iceblock
Environmental conditions play a big role in the activation of suspended animation

How is Suspended Animation Defined?

Suspended animation is an umbrella term for all kinds of pausing of biological processes. It refers to the stoppage of life that doesn't have negative effects on the organism itself - on the contrary, life in this state is protected. Suspended animation incorporates many kinds of slowed down metabolic activity. This includes hibernation, torpor, plant dormancy and even biostasis as used in human cryopreservation (where the activity is completely paused). 

It is  found in nature in a lot of large mammals and amphibians like bears and frogs in the form of torpor and hibernation. Microscopic worms and other microfauna are often capable of an even more effective type of suspended animation called cryptobiosis aka. biostasis. 

But animals aren’t the only organism capable of this. Suspended animation can also be observed in plants in a process we see in nature every year: dormancy.

“A seed enclosing the mature embryo remains in a state of suspended animation until it germinates to herald the active life of the plant. Suspension of growth of the embryo in the seed may be due to physiological states vaguely referred to as either quiescence or dormancy.” [1]

While suspended animation often happens in freezing environments, it doesn’t necessarily need cold temperatures to occur. The effect can also be chemically induced through different means, some of which can be seen in other types of biostasis such as anhydrobiosis (triggered through extreme dryness) or anoxybiosis (triggered through a lack of oxygen).

Suspended Animation in Animals

There are many animals that are capable of entering suspended animation. They usually do so to await better environmental conditions and increase their chance of survival.

The exact kind of state depends on multiple factors such as animal species, size of the organism, and type of threat.

To give one example: Turtle babies often enter a state of hibernation soon after birth, if they happen to be born under unfavorable conditions. Their hearts completely stop, and only a very low amount of brain activity can be traced. Once circumstances improve, their hearts slowly start beating again and they can start their journey of life.

Exaples of hydrated and dehydrated forms of tardigrades
Tardigrades can enter a “tun state” to slow down their metabolism to 0.01% of their normal rate. They can survive this suspended animation for many decades at a time.
(Image credit:

Suspended Animation in Humans

Unlike some animals, humans can’t enter suspended animation by themselves. Feel free to try it, it doesn’t work (and if it does, please contact us).

However, research on how we could make it work is presently being conducted. Let’s take a look at some of the options we have to induce suspended animation in humans.

Hydrogen Sulfide Trials

In 2005, American scientists conducted experiments on the effects of hydrogen sulfide on mammals. Their goal was to achieve chemically induced suspended animation on mice by exposing them to low levels of hydrogen sulfide..

The hydrogen sulfide dropped oxygen demand in the animals metabolism to an extremely low rate, which in turn meant that low oxygen supply was not lethal to them anymore. Additionally, exposure to the chemical allowed the mice to survive blood loss levels that would have been lethal otherwise. A 70% reduction in heart damage after heart attack and similarly positive results for organ damage were recorded. The trials were a resounding success and human studies began in 2008.

In response to this, biotech company Ikaria was founded with the goal to apply this newfound knowledge to humans. They were researching an injectable form of hydrogen sulfide for medical use in cardiac surgery, before the company was bought out and trials were put on hold in 2011.

Lead scientist of the project, Mark Roth, later went on to found Faraday Pharmaceuticals in 2014, which has produced similar trials for compounds intended to alter human metabolism.

Cryosleep Clinical Trials

Another test involving suspended animation, specifically a state similar to cryosleep, was successful in clinical trials. Doctors temporarily slowed down biological functions in the body by replacing the blood with an ice cold salt solution at the University of Maryland School of Medicine. 

This resulted in a substantial increase of time available to treat otherwise unrecoverable trauma patients. Lowering metabolic activity, oxygen consumption, blood flow, and tissue damage, gave doctors enough time to save their patients' lives. Currently, several hospitals use this type of induced hypothermia, through targeted temperature management, to reduce ischaemic damage in patients after cardiac arrest.

It is important to note that here, metabolic activities were lowered but not fully stopped. A complete stop of these processes would require lower temperatures and more potent cryoprotectant solutions like those used during cryopreservation.

NASA Trials

A prominent figure in suspended animation research is NASA. Together with SpaceWorks, the American space program agency has been hard at work in this field since 2013 on a project called “Torpor Inducing Transfer Habitat For Human Stasis To Mars.” Their scientists try to induce suspended animation on humans via a state called “cryogenic sleep.”

Putting astronauts’ bodies into suspended animation would greatly reduce the need for resources on the spaceship. This could allow NASA to compress regular sized spaceships from the current 20-50 thousand kg, down to only 5-7 thousand kg, which would allow them to travel greater distances with less fuel and at a lower cost.

Sleeping astronauts would take in nutrients via IV-tube, while waste is being disposed of via an additional tube system. This state is being kept for 2 weeks, after which the astronauts are being woken up again, to exercise and prevent muscle atrophy. They then return to cryogenic sleep and the cycle repeats until they reach their destination. During all this an AI is taking control of the aircraft.

Suspended animation could reduce costs of space and increase efficiency of space travel. But cryosleep approaches have their limits, as astronauts would have their metabolism slowed down but not stopped entirely. To reach distant galaxies, cryopreservation would have to be used. Ultimately, NASA sees cryopreservation as the optimal option for space travel, but reanimation is much harder than from cryogenic sleep at this point in time.

As both fall under the umbrella of “suspended animation” the two fields have the potential to positively impact each other in future research endeavours.

Looking down at earth from inside a space station
NASA’s suspended animation research started out a one of twelve futuristic ideas funded under the “NASA Innovative Advanced Concepts program”


As we mentioned before, the most effective form of suspended animation comes in the form of biostasis. Currently, the only form of biostasis with promising prospects is cryopreservation. The science of cryonics had its start in the mid 1900s and has evolved ever since. 

It is a highly specialized process that involves a multitude of steps. The first step is to stabilize and externally cool down the patients, which is conducted by a medical standby team.Then custom medical-grade cryoprotectant agents are used during perfusion, that reduce cell damage by minimising ice-crystal formations as well as internally cooling the patient. Finally, for long-term storage patients are placed inside of cryogenic storage dewars filled with liquid nitrogen to keep the body at a steady -196°C (or around 140°C in ITS systems). There can certainly be no talk of “crude freezing” when it comes to cryonics.

There is still a lot of research to do before we are able to revive patients from cryopreservation and treat their underlying causes of death. However, new technological advancements , such as the rapidly progressing science of nanotechnology, gives a positive outlook for the future - after all, that’s what cryonics is all about. To improve people’s outlooks, by providing a chance of an extended lifespan. 

We at Tomorrow Bio have made it our mission to allow people to choose for how long they want to live. For that reason, we provide full body cryopreservation services with the best technology available today, and will continue to invest in research to advance the field of suspended animation.


Suspended Animation allows living beings to temporarily “pause their life.” Animals and plants survive cold winters and wait for better circumstances thanks to hibernation and dormancy. Meanwhile humans might be capable of utlising it to increase survival rates of dangerous medical conditions and aid in space-travel in the future.

Biostasis stands out as the most effective form of suspended animation known today. Tomorrow Bio makes use of this to give people the chance to see the future and potentially live however long they want to.

Do you want to know more about biostasis and cryonics as a whole? We invite you to take a look at our newly published ebooks by entering your email address below or join our Discord server and discuss the topic with the Tomorrow team and other members of the community.

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