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    

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