X-Message-Number: 1961 Date: Sun, 14 Mar 93 23:53:51 CST From: Brian Wowk <> Subject: CRYONICS TG and all that Michael Price: >1) As far as I understand it the reason for storage at -130C is to be > close to the glass transition point (TG) where cracking is markedly > reduced over temperatures some distance below TG (say LN2 > temperatures of -196C). This seems to suppose that we have the > capability to vitrify humans *now*. The cracking problem exists, and is solvable, whether you vitrify completely or not. Here's what's going on: As you slowly reduce temperature below 0'C liquid water begins to freeze (crystalize) in tissue. As you continue cooling, there is a continually decreasing percentage of liquid left unfrozen. This unfrozen fraction (which, believe it or not, still remains liquid at even -100'C) becomes increasingly viscous as the temperature drops. Eventually, at around -120'C, the unfrozen liquid becomes as thick as glass (hence this is called the "glass transition point", or TG). Above TG, the unfrozen liquid allows movement and release of mechanical stress that occurs during cooling. Below TG, both the ice crystals and unfrozen water are now both as hard as rock so that further stress causes fractures. This means that by avoiding temperatures below TG you can prevent cracking in patients who are frozen with *current* technology. >2) Assuming we do store at -130C in a vitreous state. According to > Hugh Hixon's table in Jan 1985 Cryonics 1 sec at 37C is > approximately 6 days at -130C. So storage at -130C for (say) a > century is equivalent to over an hour's room-temperature storage. > Yikes! I have previously addressed this issue on the net. All reaction rates do not scale equally with temperature. The Arrhenius equation is extremely senstive to the activation energy of the reaction in question. To be conservative, Hugh Hixon chose the fastest chemical reaction known to biology for his study (the functioning of the enzyme catalase). The vast majority of chemical reactions in cells have much higher activation energies (and *very* much slower rates at sub-zero tempertures). Hence the table in the Hugh's article is not represenative of cellular metabolism in general. Because of this, and because of virtually non- existent diffusion at TG, we need not worry about spending a few centures at -130'C. --- Brian Wowk Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=1961