X-Message-Number: 7812
From: Brian Wowk <>
Date: Wed, 5 Mar 1997 13:15:02 -0600 (CST)
Subject: Devitrification

In Cryo Journal Club 4, Jan Coetzee writes:

>One can conclude from this experiment that it would be difficult to avoid
>crystallization during the rewarming of tissue from vitrification. Before
>one stops other freezing procedures of cryo patients one might want to give
>serious consideration to this problem.

	There are a variety things that can be done to increase the 
stability of vitreous solutions on rewarming.  For example, years ago
Boutron found that certain hydrophobic additives like n-propanol and
methyl 1,2 propanediol significantly decreased critical warming rates
necessary to avoid devitrification.  For some CPAs, glass stability 
is also exquisitely sensitive to concentration.  Increasingly the
concentration of DMSO, for example, just a few percent above CNV
produces glasses that are stable at almost any rewarming rate.
The price of these stabilization techniques is added toxicity.  But
if our initial goal is better ultrastructure, then we can afford
to add more toxicity than organ preservationists can tolerate.

	Another point is that fluorocarbon cooling also works in
reverse: After an organ has been vitrified with fluorocarbon perfusion,
fluorocarbon perfusion can also be used to warm it extremely rapidly.
We (21st Century Medicine) expect rewarming rates of 50'C per minute
for brains, and 300'C per minute for kidneys (the most vascular organ
of the human body).  These rates should be sufficient to avoid
devitrification of solutions near CNV even without RF rewarming.

	Finally, an important point needs to be made with respect to
cryonics.  Even if cryonics patients are vitrified with solutions
that devitrify easily on rewarming, then they are still better off
than cryonics patients who are frozen.  Both frozen patients and
patients vitrified with unstable solutions will require
nanotechnological repairs at deep sub-zero temperatures before they
are rewarmed, but the repairs required for vitrified patients will be
much less extensive.

***************************************************************************
Brian Wowk          CryoCare Foundation               1-800-TOP-CARE
President           Human Cryopreservation Services   
   http://www.cryocare.org/cryocare/

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