X-Message-Number: 24531
From: 
Subject: Mechanical damage by freezing 
Date: Wed, 18 Aug 2004 23:10:02 US/Eastern

In Message 24516 Basie wrote:

> In my opinion the "hamburger" effect is a lot of hooey. It does not exist.
> Maybe a little bit occurs. Where are reliable micrographs PROVING  that ice
> crystal mechanical damage occurs because of freezing. Micrographs that show
> ice crystals cutting open the membranes. Technology of our time can do that.
> People are spending a lot of time and money try to catch the wind. The
> solution might be much simpler than people think.

    The dominant opinion in the first days of cryobiology was that most
freezing damage was caused by electrolytes.  I think that more progress
has been made since cryobiologists have realized that ice is the problem. 
By trying to eliminate ALL ice -- ie, by vitrification -- the greatest strides
have been made toward the possibility of organ preservation. 

    Ice occupies a volume which is roughly 10% greater than the volume
of water. So much expanded solid material in the body necessarily 
causes mechanical damage. Most freezing occurs extracellularly when
cooling organs or cryonics patients, and capillaries are damaged by the 
expanding ice. CRYOBIOLOGY 23:300-311 (1986) has some pictures, 
and I expect that you can find others if you are willing to do the research.
Vitrification -- the elimination of ice -- is where the focus should rightly 
be on organ preservation and on the preservation of cryonics patients. 

In Message 24516 Basie wrote:

> It is not true that mechanical damage causes the membrane damage. Freezing
> destabilizes the membranes which causes the cytoplasm to leak out. By
> finding a membrane stabilizer the damage can be stopped. As long as
> scientists try to solve the "mechanical damage" problem cryonics will remain
> elusive.

    Are you talking about electrolyte damage to membranes? Or dehydration 
damage? I do believe that such damage occurs in addition to other forms
of freezing damage. Eliminating ice and protecting membranes are not 
mutually-exclusive endeavors. Trehalose is a good cryoprotectant 
because of its ability to protect membranes. But trehalose does not naturally
cross cell membranes, so it only protects from the outside, not the inside of
cells. Finding a good way to get trehalose into cells without damaging 
the membranes has been attempted by various means -- electroporation,
alpha-hemolysin, transfection of mammalian cells with bacterial trehalose
synthetase genes and thermotropic phase transition. In 1997 the latter was
used to successfully cryopreserve beta-cells from the islets of Langerhans. 
Whole organs are another matter ...  to say nothing of cryonics patients ...

                            -- Ben  

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