X-Message-Number: 1695
Date: 30 Jan 93 20:14:48 EST
From: Mike Darwin <>
Subject: CRYONICS Reply to Jeffrey Soreff re Crac

To:   INTERNET:
Date: 1/18/93

     Several people have suggested I try to answer your questions about 
the glass transition phase, cracking, polymer reinforcement, etc.  
Herewith, I give you the short version.  I don't have any complete 
answers.

     However, being never content to stop while I'm ahead, I'll go on a 
little bit further.

     The idea that weak glasses might be reinforced by a polymer is a 
clever one.  I suspect, however, that it won't work for the following 
reasons:

     1) We have for some time, used two polymers (one or the other, not 
both together) as 5% to 6% of the perfusate with which we cryopreserve 
both humans and research animals.  These two polymers are hydroxyethyl 
starch (HES) with a mean molecular weight of about 500,000 and polyvinyl 
pyrrolidone (PVP) with a mean molecular weight of 40,000.  Both bulk 
solutions and animals still crack.

     2) While I am ABSOULTELY no expert in this area I think that the 
forces involved in generating fractures ARE significant.  If specimins are 
cooled slowly you get large fractures, for instance I often saw fractures 
in rabbits completely severing the brain in several places and we observed 
fractures running over many centimeters in length completely bisecting the 
lung and liver in human cryonics patients.  Add to this a recent Russian 
observation that flashes of blue light with measured temperatures in the 
thousand plus degrees range are observed when fracturing of solutions is 
carried out in the dark.

     I cannot emphasize enough my ignorance in this area. For instance, I 
do not know if HES and PVP are "strong" enough polymers.  I would be 
delighted to carry out the experiment you suggest except that, at present, 
I have no access to liquid nitrogen.  The work we do here is all in the -
100xC range or above (since we are trying to AVOID fracturing).

     Your second question about viability is a little easier to answer.  
There are many references which fairly uniformly document rapid 
deterioration of cells and tissues stored at -80xC or above (although 
there are a few interesting suggestions to the contrary).  There are a 
small number of references that document fairly stable storage at -135xC 
or at -150xC (LN2 vapor temperature).  The bottom line seems to be that 
these are both safe long-term  (50 to 150 years) storage temperatures; the 
best evidence being that they are in common use in both ultra low 
temperature mechanical freezers and liquid nitrogen vapor freezers.

     However the story doesn't end there.  When we propose storing very 
near TG, *how* near TG becomes critical.  Some recent work by Fahy et al., 
suggests that when large masses of solution are cooled even a scant 5xC or 
10xC below TG they crack.  A lot of work needs to be done to evaluate the 
stability of water-cryoprotectant glasses at near TG.  How mechanically 
stable are these glasses?  Will the small nucleation sites known to exist 
in them grow over decades or longer periods of time (i.e., will they 
slowly freeze?).  What kind of chemistry is going on in these glasses.  
And last but not least, what is the mechanical stability of these glasses 
over time.  Anyone who has ever seen window glass in old ghost towns in 
Nevada will immediately understand what I mean: the pane is often thicker 
at the bottom and the glass has actually flowed over the frame a bit.  
Glasses kept near their TG may flow substantially with time.

     The experiments to help resolve these questions should be designed 
and started now.  

     If you want a list of references of safe cryopreservation storage 
temperatures you may call me at (909)824-2468.

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