As I understand, one of the reasons we haven’t figured out something like cryogenic sleep is that cells are irreparably damaged during the freezing and thawing process. How do we manage to avoid those problems when freezing and storing embryos for the purposes of IVF?
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Simplified answer: while there is some risk, smaller tissues/cells/etc are a lot easier to freeze and reanimate without significant damage.
The freezing process tends to introduce irreparable damage due to crystal formation. If you can control the freezing process, and/or introduce anti-freeze agents, you can pretty much mitigate this. However, larger biological samples are a lot harder to do this with. Plenty of insects and some amphibians can actually survive this, and earlier experiments with cryogenics actually showed small rodents could be reliably frozen/thawed and still live full life with little to no lasting damage. Legitimately, they did experiments where they essentially froze hamsters or mice solid and thawed them, and they were fine.
It doesn’t scale far past that, as cooling down evenly/in a controlled way, and properly infusing with anti-freeze agents and the like becomes increasingly difficult. Hence why we can’t freeze people. Freezing smaller things is still completely viable, however. We regularly do it with human cells and bacteria.
Two reasons.
First, not all cells are killed as easily by freezing as others. Ova are ones that can be frozen.
Two, If you take a dozen ova and half of them die because of the freezing process, you have six viable ova. If I freeze you and half of your brain cells die, you are very dead.
You can freeze cells, researchers do it all the time. However, it requires that you put the cells in particular medium that doesn’t form ice crystals when it freezes. That’s perfectly doable with a tube of cells, not so much with an entire person.
Also, when you freeze & thaw cells in a lab setting, a decent proportion of them will not survive the process. Also fine when you have some separate cells and are fine just moving on with the survivors, but not viable when it means half of a person’s cells die (and then the other half follows).
imagine someone asks you to reset a jack in the box, pretty easy right? now imagine some asks you to reset a large Hadron Collider. a fertilized embryo is the jack in the box, a large Hadron Collider is a live human, so so so many things could go wrong with trying to get something that complex up and running vs the former.
The challenge when freezing cells is that, when you freeze them slowly, the freezing water inside them has time to form large ice crystals. These crystals poke holes in the cells and thereby destroy them.
However, if you freeze cells very quickly (and apply some other tricks), you can make it so the ice crystals that form are very tiny and do not cause any damage (at least to most of the cells). This makes it possible to freeze living cells that are still viable when they are thawed.
So why can’t we do this to a whole human body? Or even just, like, a head? Well, the problem is that you cannot freeze them quickly enough. See, even if you apply really cold temperatures to the outside of a human body, that cold will seep into the body from the outside, in a gradual way. So, even if you can flash-freeze the outside few millimeters, the inside lags behind and still freezes slowly, meaning you get those big harmful ice crystals again.
With something as small as an embryo, this is not a problem (as long as you freeze them early enough in development).
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