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CanaryActive5296 t1_is16gfz wrote

Hello! Not an expert in freezing and thawing live specimen but well practiced in freezing and thawing dead specimen while keeping organs and microstructures intact. The major concern with freezing biological matter is the formation of ice crystals. Water forms crystals and expands when frozen and can result in burst cells and organelles. To avoid this, we introduce cryoprotectants. These are basically antifreeze that diffuse into the cells and around it to avoid formation of crystals. It's very easy to diffuse these new compounds into microscopic specimen because the surface area to volume ratio is very high compared to humans. Very rapid freezing with liquid nitrogen, also known as flash freezing, also helps in avoiding formation of large crystals (slow freezing means more time for the molecules to align). So the simple answer is size. We can't introduce cryoprotectants into every part of a human being fast enough nor can we flash freeze a human body fast enough.

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Fogl3 t1_is181bj wrote

Are these cryoprotectants dangerous? Like if we found a way to put them all inside us could we freeze ourselves? Do we just need like a wolverine needle bath?

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CanaryActive5296 t1_is1amk1 wrote

There are multiple types cryoprotectants and while they are generally supposed to be non-toxic it is only to a certain extent of concentration and exposure time. Extended exposure will interfere with daily bodily functions and metabolism. So unfortunately impossible to walk around with it indefinitely. The wolverine question is interesting because some animals have evolved to have cryoprotectants for living in the arctic or surviving winters! I don't know of any mammal that can do it but I know of at least 1 frog and 1 fish species. Info may not be updated but last I checked both are being studied to study how to preserve human organs!

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regular_modern_girl t1_is2rpvn wrote

The only vertebrates I know of that can survive freezing completely solid are ectotherms, and I’ve also never heard of any bird or mammal species being able to withstand it, so it might just be that organisms that have evolved to operate with a constant core temperature aren’t able to survive the extreme cold leading up to freezing, even besides the problem of ice crystals damaging cells? But I don’t know, that’s mostly just a guess and it may just be coincidental that no endotherms have evolved this ability.

Interestingly, there has been some evidence to suggest that critically-injured trauma patients can sometimes be kept just barely alive long enough to be saved by being cooled down to very low temperatures in a controlled setting, as I guess this basically slows down a lot of physiological processes in such a way that essentially buys doctors time to do what they need to. The procedure is called EPR, or Emergency Preservation and Resuscitation, and is still experimental, and it’s obviously still a far cry from complete freezing, but it is something.

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sbeezee t1_is6fyaw wrote

There is some evidence that spruce at Arctic treeline increase simple sugars in needle tissue in late fall as a cryoprotectant. Do you know of any other species that use simple sugars (glucose, fructose, sucrose) as cryoprotectant?

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austinmiles t1_is1ble2 wrote

At some point we could use some sort of gene therapy to introduce cryoprotectants from some single cell organisms which would be awesome

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UrbanCoyotee t1_is1mtvl wrote

I just watched a Tom Scott YT video about how microwaves were used in the 50s to reanimate frozen rats. Long story short, they were successful in reanimated fully frozen rats using microwaves...in the 1950s.

To somewhat answer your question though, it had to do with scale. They scientists who reanimated the rats found that it did not work on scale simply in laymans due to size.

He promised it was an interesting video and he delivered...

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chitzk0i t1_is2qk1w wrote

I read an article about this research. They tried to move up to slightly larger animals like rabbits, but their results because inconsistent. Small critters like mice and hamsters worked fine, though.

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regular_modern_girl t1_is2q7ew wrote

This is mostly the same thing with other cryptobiotic states as well, like in organisms that can survive complete desiccation. Often the key chemical preservative there is actually a sugar called trehalose iirc, which at sufficiently high concentrations helps to keep cellular structures intact even in the near-complete absence of moisture, such that the inner processes of the cells are basically “frozen in time” when they dry out, and therefore able to spring back to life once they’re rehydrated.

Again, this only really works with small organisms below a certain level of anatomical complexity, and I’m sure there are certain cell or tissue types that just don’t respond well to this kind of preservation, but apparently it’s part of what allows tardigrades to enter their famously nigh-indestructible “tun” state, and is also found as an adaptation in some desert-dwelling insects, and the eggs of a number of aquatic creatures that have evolved to weather extended periods of desiccation (sometimes very extended; brine shrimp eggs from literally thousands of years ago dug up in the Bonneville Salt Flats of Utah have been found to still be viable).

Even though there are several reasons it probably would never be suitable for allowing an entire human to be basically mummified and then brought back to life, trehalose has seen a lot of use as a preservative for blood or tissue samples, making it so they can be completely dried out and then reconstituted as needed (like apparently dried blood samples preserved with trehalose will even retain the distinctive vivid red of fresh oxygenated blood, rather than the dull rusty brown we usually associate with old, heavily-oxidized, dried blood).

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