While talking to my insurance agent (basically: cryonics agent) Rudi Hoffman, he mentioned something I hadn’t heard of before — intermediate temperature storage. Instead of lowering the temperature of the patient to -196 C, the idea is to lower the temperature only to -140 C or thereabouts. This temperature is low enough to freeze everything solid but warm enough that it avoids microfracturing throughout the tissue. The idea would be that it would destroy less neural information.

I hear that Alcor has been working on this approach for a while. The reason that Rudi mentioned it to me is that intermediate temperature storage, which is not yet available, may cost a bit more than conventional storage when it eventually does become available. Full body currently costs $150K. (See “The Case for Full-Body Suspension” by Michael B. O’Neal.) Intermediate temperature storage, which may be available in a few years, would require electricity and a little more maintenance to keep it going. To cover all the bases, I applied for a $250K life insurance policy, which at my age is only $26/month.

It seems difficult to find info on intermediate temperature storage on the Internet. Depressed Metabolism, the only blog I’m aware of that focuses on technical issues in cryonics, only has a couple posts on it. It looks like Cryonics Institute President Ben Best has done some research on it and wrote up his thoughts in a page “Molecular Mobility at Low Temperature” which tentatively cautions against intermediate temperature storage, mentioning the need for further research:

For Intermediate Storage Temperature (−135ºC , ~138K) the typical distance a water molecule will have been displaced over the course of a century is about 40 nanometers, whereas for −165ºC (~108K) the displacement is about one nanometer and at liquid nitrogen temperature (−196ºC ,~77K) the distance is about one-and-a-half picometers. All of these values would seem acceptable in a cryonics patient if the typical linear distance traveled by the water molecule were the same as the total distance. But the actual total linear distance (path length) traveled by the water molecule due to Brownian motion will be vastly greater than the typical displacement from the point of origin. Doing the same calculation for a water molecule at room temperature (25ºC , about 298K) using the viscosity of ethylene glycol (0.0161 Pa·s) gives a typical distance of about 1.4 meters. A water molecule at room temperature would travel a vastly greater path-length than 1.4 meters over the course of a century.

Also worrisome is the possiblility of ions within the glass that are far more mobile than the molecules constituting the glass. An ionic species (probably protons) in trimethylammonium dihydrogen phosphate glass is nine orders of magnitude more mobile than the glass molecules — and sodium ions in sodium disilicate glass are twelve orders of magnitude more mobile than the glass molecules. Water molecules can be quite mobile when in polydextrose glass, and carbon dioxide is mobile in polyvinyl alcohol (same reference).

But, molecular mobility is not lethal for northern wood frogs that can spend weeks to months in a semi-frozen state. The most damaging effects of molecular mobility at temperatures below Tg should be either from water molecules forming crystals or from mobile free radicals. Concerning the latter, cryobiologist Peter Mazur was quoted at the beginning of this piece as saying: “…there is no confirmed case of cell death ascribed to storage at −196ºC for some 2-15 years and none even when cells are exposed to levels of ionizing radiation some 100 times background for up to 5 yr.”

More experiments exposing tissues to ionizing radiation could be helpful in assessing the safety for cryonics patients of various sub−Tg temperatures above liquid nitrogen temperature. Experiments should also be done to determine the possibility of ice formation at cryogenic temperatures over long periods. More information is needed before it can be stated with certainty that damage due to molecular mobility at Intermediate Storage Temperature would not be worse than the effects of cracking damage.

It will be interesting to follow developments in that area. I would also be concerned about the reliability of suspension under crisis conditions, for instance a nuclear war. Obviously it might be easier to just pour in liquid nitrogen than use electricity in those circumstances.