Aschwin de Wolf, a cryonics researcher at Advanced Neural Biosciences, has written two new articles discussing reasons for sticking with cryopreservation as opposed to chemopreservation.

Chemical Brain Preservation and Human Suspended Animation

Excerpt:

Executive Summary

Scientific and practical considerations strongly support cryopreservation rather than chemopreservation for the stabilization of critically ill patients. Technology for achieving solid state chemopreservation of brains larger than a mouse brain does not yet exist. Chemical fixation is irreversible without very advanced technologies. Chemical fixation permits no functional feedback or development pathway toward reversible suspended animation. By contrast, cryopreservation seeks to maintain viability of the brain as far downstream as our capabilities and resources permit — an approach that reflects our view of cryonics as an extension of contemporary medicine. Cryopreservation preserves more options in that a cryopreserved brain could be scanned in future, or later chemically fixed, but the process of chemical fixation cannot be reversed and replaced by just low temperature storage. The cost benefits of chemopreservation over cryopreservation are exaggerated, largely because the standby and treatment procedures for effective chemopreservation would be just as extensive as for cryopreservation, if not more so, even assuming that highly toxic chemicals could be worked with safely in the field. Chemopreservation is being inherently tied to mind uploading, an association that is likely to limit its acceptance as a form of experimental critical care medicine by apparently requiring acceptance of the idea of substrate independent minds.

In praise of cold

Excerpt:

Some observers believe that cryonics advocates are reluctant to subject their theories to experimental scrutiny because this could damage their (uncritical) belief in future resuscitation. Similarly, one might think that cryonicists would react with a mix of hostility and dismissal to alternative strategies for personal survival. Nothing could be further from the truth. In fact, it is exactly because our personal survival is at stake that forces us to be wary of dogmatism.

For this reason, I have always been interested in chemical fixation as a (low cost) alternative for cryonics. In fact, years before all the talk about the “connectome” and “plastination” I spent considerable time exchanging messages with Michael Perry at Alcor about the technical and practical feasibility of chemical brain preservation. But no matter how open minded I tried to be about this approach, I kept running into the same challenges over and over again.

The challenge that has concerned me the most is whether a delayed start of chemical brain fixation will produce incomplete distribution of the chemical fixative in the brain because of ischemia-induced perfusion impairment. Thinking about the technical problem of “no-reflow” is not the first thing on the mind of someone who first hears about the idea of using chemical fixatives to preserve the brain. In my case, this concern was not just “theoretical.” In my lab I have spent many years looking at the effects of cerebral ischemia on cryopreservation and chemical fixation. Last year we decided to broaden our investigations to delayed chemical fixation and we have not been pleased at what we have observed so far. After 1.5 years of room temperature storage the delayed aldehyde fixed brains are falling apart and continue to decompose. In small animals one might imagine that such perfusion impairment could be overcome by immersing the brains in the fixative instead but human brains are simply too large. By the time that the fixative would have reached the core of the brain, extensive autolysis will have occurred.

TLDR: Chemopreservation can't be (and generally isn't) dismissed out of hand by cryonicists, but there are definite tradeoffs which would need to be accounted for. The bulk of the costs of cryonics have to do with needing prompt stabilization to have a decent shot at it working, and that doesn't change for chemopreservation patients.

Chemical preservation carries practical penalties, for example, in terms of the toxicity of chemicals that need to be on-hand at the deanimation site. The complete negation of cellular viability makes some kinds of experiments harder for chemical fixation (functional testing of the tissue for viability) whereas others are easier (embedding in resin for scanning). Empirical science has a place for both, but there are more practical advantages for cryonics in the clinical setting.