X-Message-Number: 3638 Subject: SCI.CRYONICS: Low Temperature Cryonics Replies From: (Ben Best) Date: Sat, 7 Jan 1995 20:31:00 -0500 I had hoped that my Low Temperature Cryonics posting (#3557) would have attracted more interest, but I am glad that Robert Ettinger and Keith Lynch provided thoughtful responses. I will answer their objections and attempt to explain my position more carefully. In response to Keith, I withdraw my comment about visible flow in window-panes that are decades old. I was referring to fuzzy transparency rather than base-thickness, but I cannot be sure how much this informal observation is the result of inferior production technique. Keith says that "the limiting factor in suspension time is radiation damage, which lower temperatures won't prevent." On this point I take the word of Brian Wowk, who has said that radiation damage is negligible because such damage in living systems is almost entirely due to the mobility of free radicals. Brian has told me that molecular mobility at liquid nitrogen temperature is so negligible that lead shielding for cryonics patients would be a waste of money. Keith also says that "The only thing low temperatures gain you are additional cracking and additional expense." Robert would undoubtedly reject the word "additional" on the grounds that CI and the Ukrainian researchers have confirmed that slow cooling to liquid nitrogen eliminates cracking. Yet Robert says, "My impression is that different kinds of damage may occur in different temperature ranges, and a longer trip is more dangerous." Bob feels that the *possibility* of additional damage between -196 C and -246 C (liquid Neon) is high, whereas I feel that the possibility is low. Both of our attitudes are based on physical intuition rather than on experimental knowledge. I think the contraction and viscosity-lowering between -130 C and -196 C would be no different from these effects between -196 C and -246 C. I feel less confident about the difference between liquid helium and liquid neon because of superconductivity, superfluidity and other such low-temperature weirdness. Both Robert and Keith seem certain that changes at -196 C (liquid nitrogen) temperature are negligible. Keith repeats Hugh Hixon's assertion that there is no translational motion at liquid nitrogen temperature. Now I must explain myself in more detail. Water molecules in a gaseous state have considerable translational motion. Water molecules in the liquid state have translational motion also, although the trajectories are quickly changed. This translational motion has a great influence upon the capacity of water to dissolve solids. Water molecules in an ice crystal have vibrational, but not translational motion -- the lattice rigidly positions each molecule in relation to its neighbors. But water can also be vitrified, as would be seen by "flash-freezing" a water droplet. In such a state, water still has both vibrational and translational motion -- although it is very, very slow. Time-lapse "photography" of the water molecules over years or decades would reveal motion similar to that of liquid water -- and presumably this also means dissolution capability. In "How Cold is Cold Enough?", Hugh Hixon used the enzyme catalase as his standard. I think this is misleading. My concern is with dissolution and hydrolysis of crushed freeze-damaged tissue and tissue fragments. Dissolution and hydrolysis proceeds far more quickly than catalase. Without knowledge of how much structural information can be lost without compromising identity, the most conservative approach is to store at the lowest temperature. Keith and Robert's assertion that liquid nitrogen is cold enough is nothing but a "gut feeling". Yet, I acknowledge that it is my gut feeling also. My argument has more bearing on my preference to be stored at liquid nitrogen temperature, rather than at -130 C. Nonetheless, I am *interested* in lower temperature storage, even though I have no immediate plans to seek it out. I view alternative courses of action (and preservation) the way a scientist views alternate hypotheses -- as ideas to keep in mind as further evidence presents itself. I also acknowledge that my water-vitrification example does not accurately reflect what happens in cryonics, so I will expound, briefly, on vitrification. In doing so, I will compare water, silica (window-glass) and sugar. Water is not very viscous, so it can be vitrified only by an extremely rapid "flash-freezing" of a small sample. Viscosity increases very slightly when water is cooled, but at freezing temperature a sudden phase transition occurs to an ice crystal. Molten silica (silicon dioxide, liquid glass), by contrast, is very viscous. This viscosity is the result of the tendency of silica to form amorphous networks of polymers rather than to arrange in an orderly crystal lattice. Nonetheless, by cooling very slowly it is possible to form rock crystal, having very high density and low volume. By cooling faster, silica will pass below its freezing temperature ("supercool") and vitrify at some glass transition temperature (Tg). Viscosity increases rapidly near Tg, but over a small temperature range rather than at a precise temperature (c.f. fusion temperature). The change that happens at Tg is simply an increase in viscosity, not a change of state. Moreover, Tg is a function of cooling-rate. A faster cooling-rate results in Tg at a higher temperature leading to a solid that has a high volume (lower density), is more amorphous and less viscous. A slower cooling-rate results in Tg at a lower temperature leading to a solid that has a low volume (higher density), is less amorphous and is more viscous. But volume continues to decrease and viscosity continues to increase below Tg. The change at Tg is quantitative, not qualitative (in contrast to crystallization). Because cooling occurs from outside to inside, overly rapid cooling creates stress when the warmer core needs to contract more than the cooler surface. I believe that this is the reason that slow cooling reduces cracking, and I believe that slow cooling is particularly important at Tg because it is at Tg that the greatest volume-reduction and viscosity-increase occurs. Sugar, like silica, can form a crystal (rock candy) or a glass (lollipop) depending on the rate of cooling. Like molten glass, liquid sugar is very viscous and prone to formation of amorphous polymers. In silica the polymerization bonds tend to be of a "mixed" covalent-ionic type, whereas for sugar the polymerization is assisted by weaker forces (van der Waals or hydrogen bonding). In neither case do these bonds have the defined bond-lengths and bond-angles of covalent bonds. Therefore, I say that molecules in these glasses have translational motion. Glycerol/water in the human body is more like sugar than like silica. But the situation is complicated by the presence of many salts, proteins, fats, etc. The lower the temperature of this brew, the more stable it will be. But this is always a question of trading-off costs and benefits -- quite a problem when the benefits are so hard to calculate. -- Ben Best () Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=3638