[LINK] blog on cryonics by someone who freezes things in a cell bio lab

Most cryobiologists don't know or care about cryonics, because it is the purview of a tiny (< 3000 peple) and eccentric minority.

The Society for Cryobiology doesn't allow cryonicists to become members and has issued statements that describe "cadaver freezing", as currently practiced by cryonicists, as an "act of faith, not science"

Though Fahy is first and foremost a cryobiologist, he has spoken at life extension and cryonics conferences, and he is not at all opposed to seeing his technology used to improve cryonics.

Does he endorse cryonics or is he signed up himself for cryopreservation?

Kinda.

If you circulate a coolant through the circulatory system, the cooling speed is limited by the coolant heat capacity and mass flow rate. For a given maximum pressure difference, the maximum flow that you can achieve depends on the fluid density, viscosity, and the structure of the circulatory system. In the simplified case of laminar flow through a stiff circular straight pipe Hagen–Poiseuille equation applies: mass flow rate is proportional to fluid density and the square of cross-sectional area, and inversely proportional to fluid viscosity and pipe length. The circulatory system is mostly made by long and thin capillaries, with curves and branching that add further resistence compared to a straight pipe.

Blood has approximately the same density of water and five times its viscosity, but it is a non-Newtonian fluid optimized for flowing through thin capillaries. With any water-based coolant, you wouldn't be able to achieve a much higher flow rate than normal circulatory flow rate, but you can use a water-based coolant since water would freeze. Anything more viscous, such as a cryoprotectant mixture, can be circulated at a much lower flow rate. That's why cryoprotectant perfusion as practiced by cryonicists takes many hours. Forcing an higher flow would not only risk rupturing the blood vessels, but also heat them instead of cooling. If you were to use cryoprotectant as a coolant (which, AFAIK, no cryo company does), viscosity would also increase as temperature decreases. And I presume that the maximum allowable pressure in blood vessels decreases with temperature: much like rubber hoses, I expect them to become brittle as they approach glass transition temperature.

Add the fact that a typical cryonics "patient" won't usually have an intact and highly functional circulatory system: hours of ischemia and pre-mortem conditions can usually result in stiff, obstructed, collapsed or outright ruptured blood vessels, making impossible to rely on circulatory function to perform cooling. In fact, it's even unclear whether proper cryoprotectant perfusion could be achieved in most cases.

Per PZ Myers, the state of the art in neural preservation doesn't recoverably preserve usable amounts of state in zebrafish brains, which are a few hundred microns on a side. How thin slices were you thinking of? And how fast were you going to be slicing?

I’ve worked with tiny little zebrafish brains, things a few hundred microns long on one axis, and I’ve done lots of EM work on them. You can’t fix them into a state resembling life very accurately: even with chemical perfusion with strong aldehyedes of small tissue specimens that takes hundreds of milliseconds, you get degenerative changes. There’s a technique where you slam the specimen into a block cooled to liquid helium temperatures — even there you get variation in preservation, it still takes 0.1ms to cryofix the tissue, and what they’re interested in preserving is cell states in a single cell layer, not whole multi-layered tissues. With the most elaborate and careful procedures, they report excellent fixation within 5 microns of the surface, and disruption of the tissue by ice crystal formation within 20 microns. So even with the best techniques available now, we could possibly preserve the thinnest, outermost, single cell layer of your brain…but all the fine axons and dendrites that penetrate deeper? Forget those.

You say no frozen human brain has been examined. Have any frozen brains been examined?

I'm not an expert. To my knowledge mainstream cryobiological techniques allow the preservation of very thin slices of brain tissue maintaining structural and functional integrity, but larger samples don't seem to be preservable with current technology (read the opinion of PZ Myers, an evolutionary biologist who studies the vertebrate nervous system and applies these techniques in his research).

Alcor, a cryonics organization, appear to have performed cryopreservation experiments on a whole rabbit brain. Apparently, they found cell membrane distortions but no ice formation. I don't know whether these results were replicated by independent researchers or even whether they were published in peer-reviewed literature. In any case, a rabbit brain is less than 1/100th of a human brain by mass, hence it is obviously much easier both to perfuse with cryoprotectants and to cool quickly.

EDIT:

What about the claims in the original link that organ transplants could be greatly facilitated if organ freezing techniques were developed. Could you comment on that claim in the context of your knowledge?

I agree that if organ cryopreservation were available, it would facilitate organ transplants. In principle perhaps you could even clone your own organs and freeze them for future use instead of keeping them alive in an animal hosts. As far as I know, this is already possible in humans for samples of ovarian tissue large enough to restore reproductive function after chemotherapy and there is animal and human experimentation on whole ovary cryopreservation.

Preservation of larger organs is not possible with current technology, and we can't know whether it will be ever be possible, since the square-cube law appears to be an obstacle difficult to overcome. If I were to guess I'd say that it will require much better biocompatible cryoprotectants to be administered pre-ischemia (or maybe even genetic engineering to make the cells produce cryoprotectants themselves, like some species of animals do) and probably also some drug (or genetic agumentation) to significantly delay ischemic damage.

It depends on how specifically it looks like in the alternative universe of the reversal test.

For example if it means "Stalin lives 6000 years, his henchmen live 600 years, other people live 60 years", then "everyone lives 60 years" could be an improvement.