>Well that's real useful... Considering that we've already established that if you get below 0C your cells explode.
Nonsense! We have established no such thing because is it not even true!
The cells *never* "explode. *If* the freezing rate is too fast then cell membranse may be ruptured since the water cannot escape into the interstitial spaces quickly enough and the small increase in density and the lack of membrane flexibility at low temperatures will cause such rupturing. However, even if human body were thrown into a Dewar of liquid nitrogen without any preparation, only the surface layer of cells would be able to cool that quickly.
In practice what happens is that cryoprotectants are perfused into the body during an operation similar to open heart surgery. These cryoprotectants enter all the cells through the capillaries of the circulation system and together with a controlled cooling rate, *all* the body's cells are prevented from rupturing. At the present time the trade-off involved is between a large cryoprotectant concentration which will totally prevent ice formation and yet will harm cells by toxic biochemical processes, and a smaller cryoprotectant concentration which will give recoverable toxicity but will not completely protect against freezing damage. Fortunately, there is a major effort underway at 21st Century Medicine to find less toxic and more ice controlling cryoprotectants and that effort is having some success.
Sorry to have to contradict you, but you could *not* place a cricket which solidifies overnight (flies do also) into liquid nitrogen and revive it. Not could you place it into a standard home freezer and revive it even a year latter. Even though it make go below freezing temperature and part of the water in it make actually freeze, the end result is still a type of hibernation - a temporary lowering of body temperature to survive a harsh environement and return to living conditions a short time later. Not all of its liquids are solidifid and biochemical activity still proceeds. I say again that no such animals or insects can last in their suspended state much beyond the standard length of time required by nature. Evolution would not have produce such life to do otherwise.
The storage of sperm and eggs is only possible with highly delicate and specialized use of cryoprotectant agents to prevent freezing damage, Even so the freezing of sperm is only possible because there are so many that a reasonable death rate is still tolerable. The recovery rate of eggs (ova) is still extremely poor mainly because of the macroscopic size of these relatively large cells. Even 8-celled embryos are only still viable because all cells are equipotent and even if 7 die the embryo can still continue.
The is no question that once the body liquids are all solidified at a temperature below -120'C (exact temperature depends on mixture of cryoprotective agents used) all chemical reations cease to occur (there is no possibility for molecules to move into reacting positions wrt each other. Since the body processes (even the brain) are entirely bases on chemical reactions, all brain processes, disease processes and aging (change/deterioration over time) will cease.
When/if you wake up you will may be chronologically 1040, but you will be biologically still 40. Since antiaging and rejuvenation methods will almost certainly be perfected by that time, in fact, you will wake up as a biological 20 year old in the prime of health and abilities but with the wisdom and knowledge of your original age.
As I have explained in detailed on other posts here, this is not applicable to the needs of human suspended animation because these animals will not last more than a normal winter season at their hibernation temperature.
Please see my other posts about why the density of water is almost irrelevant to the damage involved. If freezing is slow enough and/or cryoprotectants and ice blockers are used, there is plenty of time for water to cross cell membrances (its very penetrating after all) and no cell bursting takes place. Nor do any membranes or nerve connections need to be cut by ice formation if it it keep either small enough or non-existent which can now be done with the best vitrification methods (vitrifiction means forming a solid glass-like substance without any crystal formation taking place).
I agree with you that reconstruction of badly damaged cells due to freezing by any conceivable technology, nano or otherwise is highly unlikely. However, that does not mean that fully perfected suspended animation cannot be and will not be achieved.
Naturally occuring antifreeze proteins are much too expensive, too large and only work at relatively high temperatures, so they are hardly applicable to human cryopreservation will will need to take bodies down to at least - 120'C in order to solidify all liquids and stop all chemical processes for taking place. However, a company called 21st Century Medicine which is specializing in cryopreservation of large tissue masses has used the idea of these antifreeze proteins to construct small artifical ice blocker chemicals and is beginning to have great success with these.
In answer to your last question re "sleeping", the answer is most likely no. Even for the best of hibernating animals enormous amounts of biochemical activity continues to take place while they are hibernating. If they are kept in a refrigerator at the same temperature for much longer than the normal season length they do not revive when allowed to warm in the natural manner. From an evolutionary pov this actually makes good sense because why should evolution waste any effort in perfecting their hibernating mechanisms any more than is needed? Thus, even if we fully understood hibernation and were able to cause the same changes in a damage-free manner to humans, it would not gain us a great deal in travelling to the future when better life extension methods will be available. In addition, the process would probably not be reversible for the aged and diseased who are the ones most in need of some sort of suspended animation to get them into the hands of advanced future medicine.
The best hope is to perfect long-term suspened animation by means of cryopreservation. In that process we know for sure that all processes are stopped and, once there, no additional damage will take place for thousands of years. If we could get human to low temperatures without any damage, then the problem of using this technique to prevent death would essentially be solved. Work done with ice blockers and new cryoprotectants in recent years auger well that this last problem is solvable within 10-20 years if with could only get sufficient funding for continuing the program. The amount of funding ($100M) is trivial in terms of what major government programs receive and especially in terms of the importance of the result (truly paradigm transforming), but nevertheless promotion of this effort is not going well.
-- Paul --
Physically, you are correct about the maximum water density taking place at about +4'C. In fact, that is the reason why lakes freeze on the top instead of the bottom (where the water is denser from the pressure).
However, the change of density of water even at the freezing point has little relevance to the problems of perfecting suspended animation by means of cryopreservation. The problem is that when ice crystallizes, just as do all other substances, it tends to form a pure substance. In doing so the concentration of all the disolved chemicals is greatly increased and it is this, now-toxic, soup which caused the most damage to the tissue structures around it. Secondary damage is caused by the sharp crystaline needles of ice that are formed. Finally, a third form of damage is caused by the major differences in reaction rates of various body processes which occurs as different temperatures.
Please ask questions for more detail. It is a shame to see all these conversations taking place without anyone around who really understands the problems involved.
-- Paul --
Slashdot Mirror
Nonsense! We have established no such thing because is it not even true! The cells *never* "explode. *If* the freezing rate is too fast then cell membranse may be ruptured since the water cannot escape into the interstitial spaces quickly enough and the small increase in density and the lack of membrane flexibility at low temperatures will cause such rupturing. However, even if human body were thrown into a Dewar of liquid nitrogen without any preparation, only the surface layer of cells would be able to cool that quickly.
In practice what happens is that cryoprotectants are perfused into the body during an operation similar to open heart surgery. These cryoprotectants enter all the cells through the capillaries of the circulation system and together with a controlled cooling rate, *all* the body's cells are prevented from rupturing. At the present time the trade-off involved is between a large cryoprotectant concentration which will totally prevent ice formation and yet will harm cells by toxic biochemical processes, and a smaller cryoprotectant concentration which will give recoverable toxicity but will not completely protect against freezing damage. Fortunately, there is a major effort underway at 21st Century Medicine to find less toxic and more ice controlling cryoprotectants and that effort is having some success.
-- Paul --
The storage of sperm and eggs is only possible with highly delicate and specialized use of cryoprotectant agents to prevent freezing damage, Even so the freezing of sperm is only possible because there are so many that a reasonable death rate is still tolerable. The recovery rate of eggs (ova) is still extremely poor mainly because of the macroscopic size of these relatively large cells. Even 8-celled embryos are only still viable because all cells are equipotent and even if 7 die the embryo can still continue.
-- Paul --
When/if you wake up you will may be chronologically 1040, but you will be biologically still 40. Since antiaging and rejuvenation methods will almost certainly be perfected by that time, in fact, you will wake up as a biological 20 year old in the prime of health and abilities but with the wisdom and knowledge of your original age.
-- Paul --
-- Paul --
I agree with you that reconstruction of badly damaged cells due to freezing by any conceivable technology, nano or otherwise is highly unlikely. However, that does not mean that fully perfected suspended animation cannot be and will not be achieved.
-- Paul --
-- Paul --
The best hope is to perfect long-term suspened animation by means of cryopreservation. In that process we know for sure that all processes are stopped and, once there, no additional damage will take place for thousands of years. If we could get human to low temperatures without any damage, then the problem of using this technique to prevent death would essentially be solved. Work done with ice blockers and new cryoprotectants in recent years auger well that this last problem is solvable within 10-20 years if with could only get sufficient funding for continuing the program. The amount of funding ($100M) is trivial in terms of what major government programs receive and especially in terms of the importance of the result (truly paradigm transforming), but nevertheless promotion of this effort is not going well. -- Paul --
Physically, you are correct about the maximum water density taking place at about +4'C. In fact, that is the reason why lakes freeze on the top instead of the bottom (where the water is denser from the pressure). However, the change of density of water even at the freezing point has little relevance to the problems of perfecting suspended animation by means of cryopreservation. The problem is that when ice crystallizes, just as do all other substances, it tends to form a pure substance. In doing so the concentration of all the disolved chemicals is greatly increased and it is this, now-toxic, soup which caused the most damage to the tissue structures around it. Secondary damage is caused by the sharp crystaline needles of ice that are formed. Finally, a third form of damage is caused by the major differences in reaction rates of various body processes which occurs as different temperatures. Please ask questions for more detail. It is a shame to see all these conversations taking place without anyone around who really understands the problems involved. -- Paul --