By Aschwin de Wolf
At this time, cryonics constitutes the most popular and credible method of long term stabilization of a critically ill person in anticipation of treatment by future medicine. But cryonics does not exhaust the options available to those who question contemporary views on death. One alternative is to use chemical fixation to stabilize the structure of the brain. Throughout the history of cryonics there have been recurrent discussions whether chemical fixation can be considered a credible, or even superior alternative, to cryonics. Chemical fixation has also been advocated as a low cost alternative for those who cannot afford to make cryonics arrangements. In this article I will present a framework for how to look at the technical feasibility of chemopreservation by viewing it from three different perspectives.
The case for chemopreservation is straightforward. Let us picture ourselves a dedicated cryonics researcher who wants to observe the ultrastructure of the brain after vitrification. The researcher warms up the tissue, removes the cryoprotective agent, and uses a number of fixatives and other chemicals to stabilize the tissue and prepare it for electron microscopy. The researcher looks at the electron micrographs and is content with what he sees.
Not surprisingly, a number of people have presented the following argument: Why go through all the trouble of cryopreservation if you can stabilize the tissue with chemicals instead? Why subject the brain to the dangers of ice formation and maintenance in liquid nitrogen when chemical fixation is the gold standard for ultrastructural preservation in biochemical research? This is not a bad argument but, as is so often the case, the devil is in the details.
For good ultrastructural preservation it is not likely that one single fixative will be sufficient. Different chemicals are employed that work through different mechanisms (e.g., cross linking, coagulation) and have a preference for certain bio-molecules. For example, the expensive and extremely toxic chemical osmium tetroxide is routinely used for stabilization of lipids in preparation for electron microscopy. Depending on what the researcher wants to see, fixation protocols are tweaked to get the desired results. Which raises the obvious question: what would be the ideal protocol for long term preservation of the human brain?
There have been experiments in which glutaraldehyde, osmium tetroxide and uranyl acetate have been introduced through vascular perfusion of the lung, followed by dehydration through a graded series of ethanol (1). Perhaps perfusion can also be used to circulate a high viscosity resin. Would this be sufficient for long term preservation? It is at this point that the advocate of chemical fixation runs into a problem. Unlike the cryobiologist, the chemical fixation researcher cannot reverse fixation and test for viability. With current technologies, chemical fixation is a dead end. The researcher can use electron microscopy to inspect the intricate ultrastructure of the brain after these protocols and compare it against the best controls available but in that case he would be evaluating the adequacy of chemical fixation by…chemical fixation. The cryobiologist does not have to confine himself to this fate because he can attempt to measure viability in the brain, or even the whole organism.
Let us assume, for the sake of the argument, that the chemopreservation advocate has identified a number of fixatives (and other treatments) that are sufficient for complete ultrastructural preservation of the brain. The next question is going to be: how stable will chemopreservation be over time? This is a very important point for the technical feasibility of chemopreservation. Unfortunately, there has been little experimental research on this issue. Like the aging researcher, the chemopreservation researcher needs to develop a reliable biomarker of degradation and would be forced to rely on something like an incubator to simulate the passage of time.
For high quality chemopreservation (2) there is one formidable practical obstacle. Unless the researcher identifies a form of fixation (or vehicle) that can very rapidly diffuse through tissues, the size of a human brain requires the use of perfusion fixation to stabilize the tissue. With current technologies, diffusion fixation is too slow, resulting in extensive ischemic injury and autolysis. Unfortunately, good artificial perfusion is hard. The biomedical researcher does not have to worry about 100% complete fixation and can just use the tissue that has been fixed well. But for the advocate of chemopreservation, such pragmatism is not an option.
This raises two challenges. It is not only necessary to demonstrate that all chemicals can be introduced by perfusion fixation without perfusion artifacts, it also means that this kind of high quality chemopreservation can only be offered to those who are still alive. It is even doubtful whether this method should be recommended as a last-minute intervention. Terminally ill and agonal patients often suffer from various degrees of perfusion impairment. There are experimental protocols to overcome the so called “no reflow” phenomenon but it remains to be seen if these methods are helpful for good chemopreservation.
There are other practical challenges such as the cost and extreme toxicity of chemicals like osmium tetroxide. But perhaps if more encouraging research results are presented, economies of scale will prevail.
If chemopreservation would work there is one major advantage compared to cryopreservation – it would not require continuous maintenance such as the re-filling of liquid nitrogen dewars. For example, one could argue that if the nine cryonics patients that were destroyed in the 1970s in Chatsworth had been chemically fixed there would be a higher chance that these patients would still be preserved in some form. It is for this reason that some of us who are rather pessimistic about future social and political events, have singled out this feature of chemopreservation as an advantage.
There might be one additional argument in favor of chemopreservation. Although cryonics organizations like Alcor have been offering vitrification technologies for almost 10 years now, this fact does not seem to register with the scientific community or general public. Cryonics, as understood by most people, simply involves the freezing of dead people. Since chemopreservation does not require the use of subzero temperatures it could appeal to more people on a basic intuitive level.
As should be clear from the discussion so far, high quality chemopreservation is currently not an option but a research project. As a possible means to preserve those that cannot be sustained by contemporary medicine, it is well worth pursuing.
There is a school of thought that advocates the pursuit of chemopreservation right now. This argument can be made on two distinct grounds.
First, one can simply ignore the technical problems that surround chemopreservation and push for offering it anyway. This does not seem a prudent approach to me. If the skeptics about chemopreservation are correct, there is a risk that essential parts of the brain will not be fixed, as a result of inadequacies of the protocol, perfusion artifacts, or long term degradation. It is at this point where classic cryopreservation really shines. Even tissue that is not protected from ice formation as a consequence of perfusion impairment will still be “fixed” through low temperatures.
One could argue, however, that from the perspective of information-theoretic death there might be little difference between straight freezing and autolysis (3). In my opinion, the prospect of autolysis is much worse because when biomolecules break up into their constitutive parts, and go into solution, there is little hope of inferring the original structure of the brain. From a technical point of view, it is hard to make a credible case for chemopreservation if resources are available to choose between chemical fixation and cryopreservation.
Second, another perspective is that chemical fixation should be offered to those who cannot afford cryonics. The reasoning is that chemical preservation has enough technical credibility to prefer it to oblivion. Since this argument is identical in form to the argument that is often used by advocates of cryonics it cannot be dismissed by designating it as a form of false hope. Whether to accept chemopreservation in a less than ideal form depends on one’s estimate of low cost chemopreservation succeeding and the value that is placed on survival. Like cryonics, this is not so much a decision between being right or wrong but an issue of decision making under uncertainty.
The advocate of such low cost chemopreservation still needs to deal with a number of technical and practical questions. Low cost chemopreservation is often compared with the price of conventional cryopreservation which includes a portion set aside for long term maintenance and future resuscitation attempts. But how much difference would there be between a low cost neuro “straight freeze” with only basic maintenance and low cost chemopreservation? Is this difference of such a magnitude that an identifiable group of people would benefit from the existence of low cost chemopreservation?
The advocate of low cost chemopreservation also needs to make a number of technical decisions. What fixative(s) will be used? Who will do the fixation (the organization offering chemopreservation or a funeral director)? At what temperature will these patients be stored? There is also the issue of future resuscitation. Most people now reject third-party-funding for cryopreservation. But low cost chemopreservation (or any kind of low cost preservation for that matter) would still depend on the benevolence of future generations for resuscitation, even if the initial procedure is paid for in advance.
Unlike the advocate of high quality chemopreservation, the advocate of low cost chemopreservation does not need to delay offering the service in good conscience until there is more research but it is clear that there are a lot of practical research questions associated with this approach as well.
So far cryonics and chemopreservation have been used as mutually exclusive approaches to preservation of the person but the matter does not have to be so black and white. One can imagine a combination of chemical fixation and cryopreservation. As a matter of fact, this possibility is discussed in Eric Drexler’s book “Engines of Creation.” It should be clear that if viability is used as an endpoint, such a “chemo-cryo” combination pales in comparison to what can be achieved through cryopreservation only. At best, such an option could confer more security to those who are very concerned about the thawing out of cryonics patients.
There is another way in which chemopreservation can be combined with cryopreservation. In the last couple of years there have been a number of Alcor cases where an isolated fixed (i.e., chemopreserved) brain was loaded with a high concentration cryoprotective agent (glycerol) through diffusion to protect it against ice formation at cryogenic temperatures. There has been little experimental guidance for such protocols but is easy to imagine a research program that investigates the use of various fixatives, cryoprotective agents, and techniques to arrive at more evidence-based protocols.
There is also the question of whether patients with anticipated long transport times could benefit from some form of perfusion fixation to allow for cryoprotective perfusion or, if not technically feasible, diffusion of the isolated brain with a cryoprotective agent. Could it be that a protocol that has been used for only really ugly cases may turn out to be superior to an ordinary straight freeze as well? To my knowledge, there are no public research results available to answer such questions. Since a lot of cryonics patients fall in the category of “bad cases” as a result of prolonged ischemia, long transport times, or autopsy, the question of the role that chemical fixation can play in cryonics remains relevant.
(1) Oldmixon EH, Suzuki S, Butler JP, Hoppin FG Jr. Perfusion dehydration fixes elastin and preserves lung air-space dimensions. Journal of Applied Physiology, Vol 58, Issue 1 105-113, 1985.
(2) The possibility of normothermic stabilization through advanced nanotechnology has been omitted from this discussion because such as technology would be so different from ordinary chemical fixation that it would be better discussed as a form of suspended animation.
(3) I owe this point to Ken Hayworth, who has produced the most comprehensive review of the technical feasibility of chemopreservation to date.