It seems like the approach of cooling the organism to −30C at 350MPa, and then raising pressure further to ~600Mps to freeze it could actually solve that. As far as I understand, the speed of diffusion in water it far slower that the speed of sound (speed of sound at 25C is 1497 m/s, while diffusion coefficient for protons at 25C is 9.31e-5 cm^2/s, which corresponds to 1.4e-4 m/s − 8 orders of magnitude less), which is the speed of pressure gradient propagation. So if we use raising pressure as a way to initiate phase transition, it will occur nearly simultaneously everywhere, and the solutes won’t have time to diffuse anywhere.
ETA: I just realized that since diffusion propagates according to inverse square law, while sound is linear, they should be compared to each other at the shortest distance possible. So I checked the time it takes for a proton to cover 0.1nm (hydrogen atom diameter) in water − 5.37e-13s, which gives us 186 m/s. It’s far greater than the original number, but still an order of magnitude smaller than the speed of sound. And if we take 4nm (the thickness of a cell membrane) we have 8.59e-10s—only 4 m/s, so it decreases very quickly, and we’re pretty much safe.
That’s a very sound (pun partially intended) insight, and I don’t immediately see a significant reason for why that shouldn’t be the case.
However, humans aren’t perfectly uniform spheres of water (to borrow from a common physics joke), so some concerns do still exist. Namely: Pressure might propagate through them less predictably/quickly than just water, and different areas of the body might begin freezing at different pressures/in different orders (which can, however, be countered by raising pressures quickly).
I have updated significantly in the direction of “This idea might actually be very valuable to cryonics proponents,” for sure.
Which is why, I think, it’s better to start from sea mammals and not shrimp; imagine if, for some reason, tiny ice crystals damage blood vessels—not even due to bloodflow—and upon thawing all those clotting factors are immediately, chaotically released. It can even happen in the brain.
I’m sure I’m following why mammals should be less susceptible to this problem, can you elaborate?
Doing this with mammals has a lot of challenges though, which it’d make sense to bypass in initial experiments. The deepest dive (aside from humans in DSVs) is only 3km, which accounts for 30 MPa. I guess it’s safe to say that no mammal can withstand 350 MPa with air or any gas in its lungs, so total liquid ventilation is required, which is just as challenging to do with sea mammals as with land mammals. Also, mammals are warm-blooded, and usually experience asystole at abnormally low body temperatures, which are nonetheless far above freezing. So there’s the issue of making it survive the time it takes to go form cardiac arrest to freezing, which is also probably just as hard to do with sea mammals as with land mammals. So although the ultimate goal is to develop a protocol for humans, it’d the much easier to start with an animal that’s already capable of surviving 100 MPa of ambient pressure and +4C of its own body temperature.
I meant that in mammals of comparable sizes, you have brains with comparable sizes—and, ultimately, if you salvage a brain all is not lost. Also, they have definable behaviour, which (as you approach more harsh experiments, like the ability to recognize kin after being thawed) might tell you something useful. How would you interpret a shrimp’s ability to move after thawing? And all that blood chemistry—the closer it gets to human, the better. Starting with shrimp is useful at the very beginning, to see if it can be done at all, maybe.
As to mammals, perhaps mice are better to begin with, because they are smaller than we. I just thought—without checking—that sea mammals are tougher when it comes to oxygen depletion combined with evenly distributed heightened pressure. I can be wrong.
BTW, what do you think of Tardigrada, water bears?:)
Ah, that’s true. I guess going back to normal vitals and motion is good enough for preliminary experiments, but of course once that step is over, it’s crucial to start examining the effects of preservation on cognitive features of mammals.
Tardigrada and some insects are in fact known to survive ridiculously harsh conditions, freezing (combined with nearly complete dehydration) included. Thus, it makes sense to take a simple organism that isn’t known to survive freezing, and make it survive. I suspect though that if you can prevent tardigrades from dehydrating before freezing, the control group won’t survive, which means that some experiments can possibly be done on them too.