X-Message-Number: 12463
Date: Mon, 27 Sep 1999 16:15:55 -0700 (PDT)
From: Doug Skrecky <>
Subject: about fixation

In Message #12447 Thomas Donaldson <> wrote:

> First, we'd like to know if large organs can be completely fixed, and the
> damage that may occur during such a process simply because it may take
> some time.
>
  (I'm back from vacation)
  Entire brains and even bodies have been completely fixed. The fastest
time for immersion fixation (no perfusion) of a human brain, that I have
seen is 36 hours using a combination of aldehyde fixatives, and current
flow. (Archives of Medical Research 27(1): 37-42 1996)

> Second, unlike the case of cryobiology, I at least am unaware of ANY case
> in which an organ or tissue, even if small, has been first fixed and
> then brought back to life.
>
  The only instance of this is for fixed red blood cells, which can retain
their functionality even after being fixed. There are techniques for
partly undoing fixation, but none is completely successful for organs. An
example of this is perfusion with zinc salts to reverse some changes
brought about by formaldehyde.
  I'd like to emphasize that chemical fixation by itself is not a viable
alternative to liquid nitrogen storage, just as dry ice storage (with
current cryoprotectants) is not, since deterioration has been documented
to occur in situations where a stable glass is not formed. 
  If fixation has a place, it is only as an adjunct to other techniques
such as freezing, freeze-drying or even dehydration without freezing. IMHO
the most likely candidate for such fixation are zinc salts, which are mild
fixatives in themselves, but actually help to further reduce some
types of freezing damage, when used in conjunction with cryoprotectants.
  Again IMHO the most likely development to offer a genuine alternative to
liquid nitrogen storage is dry ice storage, when cryprotectants with a 
high enough Tg' are used (eg: sorbitol). Meats that are straight frozen
have Tg's above dry ice temperatures, and so there is no need for liquid
nitrogen for these. The need for liquid nitrogen is an artifact generated
by the use of low molecular weight, low Tg' cryoprotectants like
glycerol, which render tissue unstable at low temperatures, even as they
protect against freezing damage. No glycerol - no need for liquid
nitrogen.

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