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. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=12463