X-Message-Number: 11805
Date: Sun, 23 May 1999 11:01:01 -0700 (PDT)
From: Doug Skrecky <>
Subject: freeze drying, alcohol dehydration, osmotic dehydration

   In response to an inquiry about freeze-drying I send the following
email. I thought this might be of some interest here as well.

   The best book on freeze-drying of entire animals is one by Rolland
 Hower from the Smithsonian Institution entitled "Freeze-Drying Biological
 Specimens: A Laboratory Manual". Time to freeze-dry a human brain at -30
 C is 14 days. Weight loss was 80%.
   Note that although tissue may look good when it is freeze-dried,
 microscopic morphology of freeze-dried brain tissue is unacceptible due
 to it's high lipid content. Dehydration in alcohol gives vastly better
 results, and is much cheaper. Alcohol destroys cell membranes, but there
 is some evidence that lipid friendly ethylene glycol could be used
   One intriguing possibility is partial osmotic dehydration of tissue,
 followed by dry ice storage. Unlike procedures using harsh chemicals like
 alcohol, cellular viability may still be possible. Hydrogen bonding of
 the remaining mostly unfreezable water would stabilize morphology so that
 the results would be much better than for complete dehydration. Tg' of
 frozen tissue is above dry ice temperatures, so that if it is not
 depressed by exogenous cryoprotectants dry ice storage should prove
 feasible. This is not too much different from current cryonic procedures
 which mostly afford cryoprotection from dehydration, rather than
 permeation of glycerol, which passes through the blood/brain barrier only
 very slowly. The main change would be to substitute something with a
 higher Tg' like sorbitol for the glycerol, which is also freely soluble
 in water. A longer period of perfusion should osmotically dehydrate
 tissue to the extent that ice formation upon freezing would be reduced to
 low levels even if no cryoprotectant passes into the tissue.

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