X-Message-Number: 33242 From: Date: Sat, 15 Jan 2011 23:50:27 EST Subject: Response to Metzger & Base Part II > In other words, the ice that makes the solution milky which is > most of the ice that will form in a 7.5 M glycerol solution - is > ice that formed in a deeply supercooled state.This happens even in > the absence of ice blockers because this is how concentrated > cryoprotectant solutions behave when cooled slowly to below their > freezing point. Thus, ice formation in supercooled solutions in > cryonics patients is not a new phenomenon that began with > vitrification. Yes, that last sentence (which is one of the punchlines in your note) is almost certainly true. > As Brian points out: "It should also be clear from > this that idea of nucleating high molarity glycerol solutions > externally would not have achieved anything because such nucleated > ice, like those ice balls in the flask formed near Tm, could only > have grown a few millimeters into the solution before cooling was > complete. The same goes for any ice that nculeated at higher > temepratures inside the patients in poor perfused areas. Well, this sounds plausible, but I don't have a well validated model here of what's going on in a uniform solution, and biological tissues are very different from a uniform solution, so it is hard to know how well that applies in tissues. It is, I think, a mistake to believe you understand something simply because you have a plausible but unvalidated model. Experiments would probably be needed to determine the answers for real. MD: I too would be happier if there were more robust experiments and I suspect they are done or are being done at 21CM, but have no way of knowing. I've not been there in ~10 years, and maybe longer.>> > In parts of the brain that experienced good equilibration with the > high concentration solution, the penetration of ice from other areas > would be minimal, and most of the ice that formed in well-perfused > areas would be formed under conditions of deep supercooling. Presuming that the explanation of the opacity in the cooled solutions is indeed homogenous nucleation of some sort, this is again potentially plausible. Of course, tissues are very different from a uniform solution -- some components of the tissues might promote nucleation at much higher temperatures, might impede nucleation, etc., and in any case, the contents of cells and tissues are very non-uniform. MD: Yes, and in any event, I am very unhappy with cryonics organizations calling what they are currently offering 'vitrification.' In most patients, vitrification will be inhomogeneous due to perfusion defects and I think that some other, more accurate and more descriptive term should be employed, possibly something like, Inhomogeneous Vitrification (IHV) or Very Low Ice Cryopreservation (VLIC). That would also be an incentive for the COs to develop a method of determining both WHERE and HOW MUCH ice is forming in patients and both correlate that with the patient's medical history and Transport and CPA perfusion care.>> > You > can bet whatever "blasted areas" or ice holes were seen in your > 7.5 Molar 1995 canine brains were areas hit by ice that started > growing in a very supercooled state." What I take away from this > is that ice will still form and grow extracellularly under > conditions where the colligative CPA concentration is very high > and the solution is very viscous. Where nucleation and ice growth > occur close to the melting point of the solution (Tm), the ice > formed will be 'large mass' ice, and likely mechanically > disruptive. Where ice forms well below Tm, it will likely be in > microscopic domains that still begin forming (nucleate) outside of > cells and consequently do little damage. Again, extremely plausible, but this is a question which actual experiments could answer, and in fact very quickly. Now, going beyond all that we've discussed up to here, this whole topic brings to mind a very basic question: has anyone in the cryonics world or cryobiology world done a deep exploration of the physical chemistry literature on the formation of glasses at low temperatures? MD: You can probably bet next to your bottom dollar that 21CM has a veritable digital mountain of data on this. In fact, while Brian got his Ph.D. in Medical Physics (imaging) he is now more properly a physical chemist specializing in the behavior of water at low temperatures in the presence of CPAs. His medical physics Ph.D. is probably nearly useless now, - judging by the stunning advances in both imaging and treatment I'm seeing emerging in research and medicine. For instance, direction diffusion tensor imagine now allows sub-millimeter resolution of the brain in humans, and considerably better in rats. Thus, it is now possible to map the general pathways of the white matter circuitry - and a consequence we are getting our first picture of just how devastating so called normal aging is to the human brain. I won't digress further here beyond saying that by the time you are 40 you are already f#%&@, big time.>> I have to admit that until a few years ago I wouldn't have even thought to ask if such a literature existed, but I'm now no longer so ignorant. My suspicion is that the pchem guys know a whole lot more about this topic than most of us, and have a lot of understanding about the competition between crystal and glass formation and what shifts the equilibrium one way or the other. I'm unsure as to whether we would learn anything valuable by exploring that topic in depth, but there is a good chance we would. Knowing what things are like in most of science, I suspect that the pchem guys and even conventional cryobiology types have never really talked, though of course I could be entirely wrong on this. Anyway, it doesn't hurt to ask... MD: There is an exploding literature on these topics with entire books coming out just on the subject of Tg. In fairness, so much data is being generated that it would take a team of specialized cryobiological physical chemists to stay on top of it. But then, this is the case in so many areas of science - even cerebral ischemia and the related area of neuroprotection, the literature is simply impossible to track and absorb.>> Message #33232 From: "Eisab" <> References: <> Subject: latent heat of fusion Date: Fri, 14 Jan 2011 21:34:58 -0500 "Despite the control applied to the cooling of cells, most of the water present will freeze at approximately -2 C to -5 C. The change in state from liquid to crystalline form results in the release of energy in the form of heat; this is known as the latent heat of fusion. Warming of the sample occurs until the equilibrium freezing point is reached, at which temperature ice continues to form. To minimize the detrimental effects of this phenomenon, undercooling must be minimized by artificially inducing the formation of ice. This can be accomplished by seeding the suspension with ice or some other nucleating agent, or by rapidly dropping the temperature of the external environment to encourage ice crystal formation." http://www.nalgenelabware.com/techdata/Technical/cryo.pdf I wonder if the latent heat of fusion is a big problem in cryonics. Basie MD: It used to be a proverbial pain the fanny, when we were freezing with low molarity concentrations of colligative agent. But with the advent of high molarity cryoprotection, and much more aggressive cooling, the amount of ice formed is so small that it is not much of a problem, if any. And of course, in vitrification there is no latent heat of fusion and any energy released in moving through Tg is both smeared out (rather than abrupt) and VERY small, compared to that seen with ice formation. Mike Darwin Content-Type: text/html; charset="US-ASCII" [ AUTOMATICALLY SKIPPING HTML ENCODING! ] Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=33242