If you freeze cells quick enough, it prevents ice crystals forming and so the cells can be stored frozen. This is used already with small bundles of cells.
The problem for achieving suspended animation, though, is how do you freeze something as big as a human body quickly? If you just dunk it in liquid nitrogen, it will take a while for the cold to permeate, and the inner cells will not freeze quick enough to avoid the dreaded ice crystals. Result: when you dethaw your astronaut/time tourist/terminally ill patient in the future, you just get a lot of mush.
This is where magnetic cooling comes in. When you apply a magnetic field to a magnetisable material, it heats up; when you switch off the field, it cools back down. This is because of entropy and different characteristic curves or some such bollocks; anyway, it?s a well-established phenomena.
So, you've got your volunteer. You give 'em a general anaesthetic (they probably don't want to be awake through the next part). You then insert tubes into some of their major arteries and veins, and pump out all their blood, while simultaneously flooding their body with the ferroliquid - tiny magnetisable particles suspended in a liquid. (Designing your ferroliquid is going to be the tricky part. Some materials are much better at magnetic cooling than others, e.g. gadolinium. Also, it has to be non-toxic, and an appropriate pH, etc).
The magnetic cooling effect is very small, only a matter of a few degrees at most, so the liquid would have to be cooled as it was pumped in. You would probably have to suffuse the body several times to get all the tissue close to zero degrees Celsius, as your liquid can never be below that or you would get areas of freezing, with the dreaded ice crystals. (Obviously at some point in the cooling process you would have stopped the heart.)
This whole process is carried out in a strong magnetic field. When the whole body has reached just above zero degrees C, you just switch off this field, and every magnetic particle in the body instantly(well, pretty damn quickly) cools down a couple of degrees C. The cells, surrounded by the ferrofluid, are cooled down with it, and hey presto, the entire body is frozen solid, with no ice-crystals. You then just transfer said volunteer to the freezer, and wait till its time to revive them(probably using a reverse of this process).
Of course, this does require the use of very high, very uniform magnetic fields. But as luck would have it, that's exactly what MRI scanners are designed to produce, so you could just use one of them.-- spacemoggy, Dec 01 2003 Magnetic Cooling http://www.ameslab....all97/bigchill.htmlDescription of magnetic cooling [spacemoggy, Oct 04 2004, last modified Oct 06 2004] Suspended animation, Inc http://www.suspende...c.com/services.htmlDetailed description of current cryopreservation procedure [spacemoggy, Oct 04 2004, last modified Oct 06 2004] Gadolinium(click on the "magnetic refrigeration" link for pdf) http://amtc.org/Code/product_rd.htmA little bit about the properties of gadolinium [spacemoggy, Oct 04 2004, last modified Oct 06 2004] Link about fast freezing of cells http://www.ivf.com/freezing.html [spacemoggy, Oct 04 2004, last modified Oct 06 2004] Suspended animation http://www.halfbake...spended_20AnimationA previous Halfbakery idea for achieving suspended animation, that sort of inspired this one [spacemoggy, Oct 04 2004] Your procedure sounds like the standard procedure for cryogenically freezing people popular with the sci fi press, only with "ferrofluid" substituted for "magic freezing liquid of the author's choice".-- DrCurry, Dec 01 2003 <spacemoggy> Use the links function please.-- sufc, Dec 01 2003 uh, sorry... let me just sort that out.-- spacemoggy, Dec 01 2003 Better now?-- spacemoggy, Dec 01 2003 [DrCurry] I don't see how having magnetic particles in the bloodstream is significantly different to having red blood cells, assuming they were small enough. Also, they wouldn't penetrate the cells, and they wouldn't expand on freezing, which I think is what makes the ice crystals so destructive.-- spacemoggy, Dec 01 2003 Interesting concept. But I am leery of using magnetic cooling in a biologic system. If you are using a strong magnetic fluid, why wont the strong field tear it right up and out of the tissues? Anyone who has watched the second Xmen movie will be aware of the potential trouble this could cause (Magneto uses this method to dispatch a person who has been doped with magnetic fluid, or iron, or something).-- bungston, Dec 01 2003 Result: Dead Volunteer -- Perhapse you could practice on cadavers to get this "Execution Machine" perfected? ... then again, I'm no MEDICAL doctor-- Letsbuildafort, Dec 01 2003 Yeah, thats a good point Bungston. Had to admit I hadn't thought of that. Spent the last hour trawling the web trying to find out whether it would kill Mr. Volunteer. I think maybe it wouldn't - if you used this stuff called gadolinium as your magnetic material, then at zero celsius you could get a 3 degree change in temperature for a field change of just 1 Tesla. This is quite big, but I'm pretty sure its not big enough to "do a Magneto".
So hopefully no executions. And a few dry runs would probably be a good idea. Although I don't want to offend any animal lovers, would an animal trial first be acceptable? You could save a sheep from the abbatoir, and promise it it's freedom if it survives.-- spacemoggy, Dec 01 2003 You are trying for a "supercooled" state where the fluid does not have a chance to make ice crystals. Would a sudden drop of 3 degrees be more effective at preventing this than a gradual cooling over this same range? Colder is colder, and I am not sure how speeding up part of the cooling process avoids the "mush" end result you describe.-- bungston, Dec 01 2003 I thought that the problem developed during thawing, not freezing.-- Detly, Dec 01 2003 I remember reading recently that the "magneticisity" (my term) of current ferrofluids is relatively weak, anyways, in comparison to other magnets.-- RayfordSteele, Dec 02 2003 [Zanzibar] Can you be more specific, please? Which aspect do you not like?
[Bungston] & [Detly] Here is an extract from a web site that discusses the freezing of cells:
"Alternatively, traditional cryopreservation protocols which impose 'slow' cooling rates of about minus one to two degrees Celsius per minute might be replaced by more ultrarapid freezing technology. Vitrification refers to a form of cryopreservation where cooling rates are so rapid (>minus 20,000o/minute) that ice does not have a chance to form, and the mixture of cryoprotectant and egg forms a 'glass-like' gel. The first reports of success with this approach have very recently come from Italy and South Korea. From a practical standpoint, vitrification is very simple and actually removes the need for the expensive programmable controlled-rate freezers currently used to freeze egg and embryos." I've included the link above.
[RayfordSteele] The key point here isn't the magnetic susceptibility of the material, but how it changes its temperature in response to a magnetic field. And I'm not just talking about using any old ferrofluid. The particles would be made of something specially developed for magnetic cooling, such as gadolinium. See gadolinium link for details of how it reacts to magnetic field.-- spacemoggy, Dec 02 2003 Ah. Now if we could figure out how to extract all of the blood out of a person in a short enough timeframe to keep them alive.-- RayfordSteele, Dec 02 2003 Too harsh, [Zan]. There exist organisms which withstand freezing and stop breathing. Presumably something changes about the oxygen demands of the brain under these conditions. I am not sure [mogs] idea would work, but I think the halfbakedness of it is right in the HB strike zone. And for [mogs] - the main reason I don't think it would work is that at the heart, it is a method for rapid cooling and I doubt that it is technologic barriers to rapid cooling which prevent human cryopreservation. For example, regarding the liquid nitrogen: you cannot cryopreserve a (living) fruit fly using this stuff, although I am sure they freeze solid in an instant.-- bungston, Dec 03 2003 What if you bumped them? (sound of shattering body parts)-- DesertFox, May 06 2004 I agree with [bungston] and think this idea should stay. [Zanzibar], please rescind your mfd.-- bristolz, Jun 08 2004 Wouldn't the high magnetic field cause problems with the fluid during pumping?-- Freefall, Jun 08 2004 How so?-- spacemoggy, Jun 14 2004 random, halfbakery