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Do we have the technology to freeze people and brind them back to life? What would happen to the water in our body if we were frozen, wouldn't it expand...and isn't this a potential problem to freezing humans?
Answer 1:

I think the state of the art right now is that we can routinely freeze cells and bring them back to life. People often freeze things like embryos (human and animal) and bone marrow (stem) cells in case they are needed later. These cells have to be put in a fluid that keeps water from crystalizing when it freezes. Otherwise the water crystals will puncture cells walls and cause damage.

Freezing humans is quite a bit more complicated and is only attempted on people who are already dead due to other causes. People hope that if they are frozen that they can be defrosted, repaired, and brought back to life by future medical technology. We don't have the capability now.

Answer 2:

There are many problems involved with freezing living tissue successfully.The biggest problem is that most tissue is 70-90% water, with salts, proteins, etc. dissolved in it, at least while the water is liquid. When you freeze a liquid like water with things dissolved in it slowly, the salts and other important parts are removed from the growing ice crystal. This is a common method to purify things, and is pretty common to chemistry classes - purification through crystallization. You wind up with pretty pure ice, surrounded by a solid goo of what used to make the living creature. This segregation tends to break down membranes, disrupt organelles and cells, and pretty much destroy any hope for staying alive once re-melted. The only common things frozen are human sperm cells - they are very tiny cells, and not particularly complicated. If you put the sperm in the correct fluid, and freeze rapidly, then it is possible to thaw the sperm back out and it remains living. For larger cells, it is very difficult to freeze and thaw individual cells successfully. Human blood cannot be frozen and re-thawed for use, for example. There are research projects underway to try to figure out how to freeze blood so it can be preserved longer. As far as I know, it is impossible, at present, to freeze and thaw an entire creature.
Some single and multicell animals, like yeasts and some bacteria, can be frozen and re-thawed slowly. These cells, when it starts to get cold, or their world starts to dry out, can successfully dehydrate themselves, and make the fluids in the cell very concentrated with high molecular weight sugars and proteins. These prevent the water in the cell from crystallizing - the water forms a solid like glass and the solutes are not removed from the solid water. However, most plant and animal cells are not really capable of this. You might try an experiment at home with some salty water and an ice cube tray. Freezing the salty water will lead to a segregation of the salt and the pure water ice.

Answer 3:

We do not currently have the technology to freeze people and then to bring them back to life. You are completely correct in saying that the water in our cells will expand and cause problems. The expansion of water as it freezes can rupture cells, causing irreversible damage. This breaking of cells during freezing is responsible for much of the damage that occurs when someone gets frostbite. Some people think that one of the main challenges in being able to put people into cryogenic suspension (freezing them so that they can be revived) is going to be the development of some type of "antifreeze" -- a compound that can be put into the body to prevent the rupturing of cells.

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