X-Message-Number: 7532
From: Brian Wowk <>
Date: Sat, 18 Jan 1997 23:44:23 -0600 (CST)
Subject: SCI.CRYONICS Supercooling

Ray Sheely <> writes on CryoNet:

>NOTE:  This is my first attempt at posting on CryoNet.  If my message is
>somehow inappropriate, please feel free to politely say so.

	Not at all.  I wish there was far more technical discussion
here.   

>Everyone knows water can be kept in a liquid state when its temperature is
>lowered below 0 degrees C by continually agitating it (supercooling).

	Supercooling (wherein a liquid remains liquid below its freezing
point) occurs when solutions are rapidly cooled in absence of heterogeneous
nucleation sites (dust particles, surfaces, etc.).  I'm not aware of
agitation being a factor.  If anything, agitation promotes freezing in
cryoprotectant/water solutions.    

>IF the aforementioned agitation could be effectively propagated sonically,
>then could this process be applied in such a way to decrease "freezing"
>damage when freezing organic tissue....?  
>Has anyone tried
>experiments towards this end, and how expensive would it be to try it?

	The suggestion has been made previously on CryoNet, but I 
don't know if anyone has ever tried it.  I myself am disinclined
to look into it without further evidence (theoretical or empirical)
of utility.  I've seen supercooled cryoprotectant/water solutions
freeze before my eyes when they are stirred slightly.

	However you are right on the mark about supercooling being
a very non-damaging (in principle, zero damaging) method of
cryopreservation.  The most effective way known to aid supercooling
of water is to add solutes that depress the homogenous
nucleation temperature (Th)-- the temperature below which supercooling
cannot continue.  Chemicals that do this effectively are known
as "good glass formers".  They also have the added benefit of
decreasing the rate of cooling necessary to achieve supercooling.
If you add enough glass former so that Th meets Tg (the glass
transition temperature), you can supercool all the way down to
a stable glass.  This is called VITRIFICATION, and is currently the
most promising technology for long-term cryopreservation of
organs and perhaps eventually whole humans.

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

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