X-Message-Number: 21732 From: "Igor Artyuhov" <> References: <> Subject: Pressurized and frozen food for thought (Re: CryoNet #17788, a bit late ... :) Date: Sat, 10 May 2003 01:53:07 +0400 Both articles [1, 2]* mentioned by Ben Best in CryoNet #17788 seem to me of great interest for cryonicists. In fact, the method, now known as High-Pressure Shift Freezing was (AFAIK) first applied experimentally as long ago as 1967 by Maxim Persidsky in an attempt to preserve a canine kidney [3, 4]. The kidneys exhibited less signs of tissue deterioration then kidneys, frozen by any other method, but still were not viable. I don't know about any subsequent attempts in this direction. Later the method was re-invented under the name HPSF in order to achieve high-quality preservation of food. Today the area is under a rather extensive exploration; the outcome is mainly presented in "Journal of Food Sciences" and "Food Technology" (see list of references in [1]). The main idea of the method comes from the fact that, applying sufficient pressure to water we can reduce its melting temperature (Tm). At a pressure of 210 MPa (~2100 atm) Tm is -22C; further increase in pressure results in the rise of Tm. It was two or three times mentioned in the CryoNet messages (## 5077 et al.) It is hardly practical to store either food or human bodies at 2100 atm; as well, -22C is far from the temperatures of interest for cryonicists. But the good news is that when pressure released - and that can be done very quickly - we get the water in the sample being supercooled to -22C at atmospheric pressure. In the absence of cryoprotectors and ice-blockers it will soon - in a few seconds - change into ice. But the crystals will be 1. Very small 2. Granular shaped (vs. needle-shaped, when cooled from the surface) 3. Uniformly distributed all through the sample. So, the damage from ice crystals will be much less than in case of surface cooling. Not all of the water will freeze. Since the freezing produces much heat, the sample will warm to 0C when about 29% change into ice [1]**. So, HPSF only is not sufficient for cryonics. Several methods can be applied in order to handle remaining 71% of water: Usage of cryoprotectants. In fact, application of pressure can reduce the necessary concentration of cryoprotectant by 0.29, for example from 27% to 19%. Cyclic freezing. Persidsky [3, 4] used combination of cryoprotectant (15% DMSO) and several compression - cooling - releasing cycles. Supercooling. The temperature of homogenous nucleation (the ultimate temperature to which water can be supercooled) goes down from -40C at atmospheric pressure to -90C at 2100 atm [5]. So, in theory, water can be cooled down to -90C without crystallization. In this case the heat of phase transition will not be enough to warm the water to 0C and it will all change to ice immediately after the release of the pressure. Usage of cryoprotectors and ice-blockers may help to achieve the necessary degree of Supercooling. Of cause, any combination of these methods is possible. Another possibility is to use vitrification rather than freezing. Under high pressure the viscosity of water greatly increases, up to 1500 times at 2100 atm [5], thus greatly reducing the nucleation rate. The high pressure method allows specimens up to 0.2 mm thickness with a total volume of ~1 mm^3 to be vitrified without any cryoprotectants at cooling rate of 200C/sec (vs. 10000 C/sec at atmospheric pressure) [5]. And, as in case of supercooling, cryoprotectors and ice-blockers may help. High pressure can as well be used on the thawing stage to reduce the recrystallization. Bad news is that application of such pressures as 2000 atm leads to denaturation of some proteins [6]. It is hard to say now whether this kind of damage is inappropriate for cryonics purposes - as compared to crystallization, osmotic shock, cracking etc. It is possible, that more compression - cooling - releasing cycles with say, 1000 or 500 atm pressure will do better. Of course, 2100 atm chamber for whole body will be rather an expensive piece of equipment. But, if they can afford it for food processing, can't we afford it for processing ourselves? __________________________ * Both papers aren't available via Internet, but I can send copies of them as PDF files on a request. ** In fact, one should consider the total thermal capacity of the sample/body rather than just capacity of water. So it may take much more than 29% of water to crystallize to warm all the tissue to 0C. References 1. L. Otero, P. D. Sanz, "High-pressure shift freezing. Part 1. Amount of ice instantaneously formed in the process", Biotechnology Progress, 16(6):1030-6, 2000 Nov-Dec. 2. P. D. Santz, L. Otero, "High-presssure shift freezing. Part 2. Modeling of freezing times for a finite cylindrical model", Biotechnology Progress. 16(6):1037-43, 2000 Nov-Dec. 3. M. D. Persidsky, V. Richards, "Cryopreservation of Organs in the Absence of Thermal Gradients", Cryobiology, March-April, 1967, pp. 375-376. 4. M. D. Persidsky et al., "Dog Kidney Cryopreservation Under Thermal Gradient-Free Conditions", Cryobiology, March-April, 1968, pp. 264-265. 5. "HPM 010 High Pressure Freezing Machine" http://www.bal-tec.com/products/PDF/HPMGRE.htm Rate This Message: http://www.cryonet.org/cgi-bin/rate.cgi?msg=21732