X-Message-Number: 3353 From: Ralph Merkle <> Subject: CRYONICS Chemical fixation Date: Tue, 25 Oct 1994 18:28:11 PDT >From "Molecular Repair of the Brain" (URL ftp://parcftp.xerox.com/pub/merkle/techFeas.html): As an aside, the vascular perfusion of chemical fixatives to improve stability of tissue structures prior to perfusion with cryoprotectants and subsequent storage in liquid nitrogen would seem to offer significant advantages. The main issue that would require resolution prior to such use is the risk that fixation might obstruct circulation, thus impeding subsequent perfusion with cryoprotectants. Other than this risk, the use of chemical fixatives (such as aldehydes and in particular glutaraldehyde) should reliably improve structural preservation and would be effective at halting almost all further deterioration within minutes of perfusion[67]. The utility of chemical preservation has been discussed by Drexler[1] and by Olson[90], among others. 1. "Engines of Creation" by K. Eric Drexler, Anchor Press, 1986. 67. "Fixation for Electron Microscopy" by M. A. Hayat, Academic Press, 1981. 90. "A Possible Cure for Death" by Charles B. Olson, Medical Hypotheses 1988 Vol 26, pages 77-84. The use of chemical fixation is debated from time to time and would seem to offer definite advantages. Current suspension methods do not preserve function, and the evidence that they preserve structure is at present based largely on light and electron microscopic images. If we wish to produce the best possible light and electron microscopic images (and hence provide the best currently obtainable evidence of structural preservation), it would seem natural to adopt the methods developed over many years by microscopists interested in high quality images. The reluctance to adopt chemical fixation appears to stem from 4 sources: 1) We have less experience with chemical fixation followed by perfusion of cryoprotectants followed by freezing, and in particular we need evidence that chemical fixation can be done in a manner that leaves the circulatory system available for the subsequent introduction of cryoprotectants. Futher, chemical fixatives are not always benign. Spilling glycerol is unlikely to harm the suspension team, while exposure to glutaraldehyde or osmium tetroxide would be significantly more damaging. Thus, procedures for the safe handling of the chemical fixatives would have to be adopted and followed. 2) The use of chemical fixatives would appear to require an explicit up-front decision to depend on the future development of nanotechnology, completely abandoning the (in my opinion rather remote) hope that someone suspended with current technology might be revived in the future by a technology that was simpler and more easily developed than full blown nanotechnology. 3) The use of chemical fixation by itself (without subsequent freezing) appears less attractive because of the uncertainty surrounding the long term effectiveness of chemical fixatives in blocking further deterioration. Freezing to the temperature of liquid nitrogen offers a virtual guarantee that subsequent deterioration will be insignificant. 4) Inability to perfuse all regions of the brain (which might occur if clots or other blockages are present in the circulatory system) can prevent chemical fixation of some regions, thus resulting (in the absence of freezing) in complete deterioration of those regions. Cold, on the other hand, is guaranteed to penetrate to all regions of the brain (even though blockage of the circulatory system might result in a "straight freeze" of those regions). Objections (3) and (4) can be avoided by freezing the tissue after fixation and perfusion with cryoprotectants. Objection (2) is (in my opinion) rather weak. I think current suspension damage is sufficient to insure that technologies significantly simpler or less powerful than full blown nanotechnology are unlikely to produce satisfactory results. Effectively, we are already dependent on the future development of nanotechnology. It is possible that advances in suspension technology might change these conclusions in the future -- at which point a re-evaluation of the available alternatives might be appropriate. Objection (1) thus remains as the major impediment to adoption of chemical fixation as an adjunct to freezing. This objection, however, is primarily based on the relative absence of experience in the use of this approach. This could be changed, given a sufficiently motivated effort. To date, there have not been enough people who felt that chemical fixation offered sufficient advantages over the present methods to fund and staff the needed effort. It looks like a lot of work. I would expect, as cryonics grows, that at some point this approach will be investigated more seriously. Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=3353