Cryonic freezing

[wheel]

I read some facts from the Internet that this cryonic freezing technology is used to freeze dead bodies at very low temperature around the boiling point of liquid nitrogen. At such temperature, dead bodies can definitely be prevented from being decomposed. According to the resources, this preservation of dead bodies is done because future technology might be able to revive the dead people. Is this one of the purposes of preserving the dead bodies using cryonic freezing?

I understand that human sperms are also froze using this technique in the sperm bank. When cells freeze under normal condition, the frozen water inside the cells will cause the rupture of cells. My doubt is, how can cryonic freezing helps to prevent the sperms from rupturing?

[canalon]

To store sperm or cells you add antifreeze to the mix (DMSO, glycerol,...) that will prevent the formation of big ice crystals, by creating multiple nucleation sites (so plenty of very small crystals) and hence reduce the risk of membrane rupturing.

As for the freezing of whole body, I listened a few months ago a conference from someone studying how frogs and other animals can survive freezing temperature. And at the end he explained why cryonics is a joke (besides the fact that you might wonder why the hell anyone would care resuscitating you in the future...). The main points were:
- a human body is too big to freeze fast enough
- a frog brain is good for ribit ribit, but not much more, hence it seems to be able to withstand much more damage than any mammal, or ape.
- The mechanisms used to protect frog cells would kill your cells quite fast

[wheel]

Do you mean only small ice crystals may form inside sperms stored in sperm bank?

[biohazard]

Yeah, you have to do it like Canalon said and use certain additives (cryopreservants) in order to freeze sperm without rupturing the cell membranes by ice crystals. In cell size-scale, small crystals are okay, huge crystals puncture the membrane.

And since this applies pretty much to all animal cells, large animals (here, humans) cannot be frozen that way, since you cannot A) distribute the cryoprservants efficiently, and B) freeze (or thaw) the body fast enough from all parts. Although you can freeze cells too fast also: if you simply toss your cells into the liquid nitrogen, they probably die regardless of cryoprservants, but if you first freeze them a bit slower (e.g. in a freezer), the results are better.

(Some) bacterial cells, on the other hand, are more robust and can often be succesfully frozen even without cryopreservants.