Critical Warming Rate Research Articles

Vitrification cryopreservation of ligaments based on zwitterionic betaine

Ligament cryopreservation enables a prolonged shelf life of allogeneic ligament grafts, which is fundamentally important to ligament reconstruction. However, conventional cryopreservation techniques fail to eliminate the damage caused by ice crystal growth and the toxicity of cryopreservation agents (CPAs). Here, we report a novel CPA vitrification formulation primarily composed of betaine for ligament cryopreservation. Comprehensive optimization was conducted on the methods for vitrification and rewarming, as well as the loading and unloading conditions, based on the critical cooling rate (CCR), critical warming rate (CWR), and permeation properties of the cryoprotectant. Using biomechanical and histological level tests, we demonstrate the superior performance of our method in ligament cryopreservation. After 30 days of vitrification cryopreservation, parameters such as the Young's modulus, tensile stress, denaturation temperature, and glycosaminoglycans (GAGs) content of the ligament remained essentially unchanged. This work pioneers the application of ice-free cryopreservation for ligament and holds great potential for improving the long-term storage of ligament, providing valuable insights for future technique development.

Perspective: A Guide to Successful ml to L Scale Vitrification and Rewarming

Cryopreservation by vitrification to achieve an "ice free" glassy state is an effective technique for preserving biomaterials including cells, tissues, and potentially even whole organs. The major challenges in cooling to and rewarming from a vitrified state remain ice crystallization and cracking/fracture. Ice crystallization can be inhibited by the use of cryoprotective agents (CPAs), though the inhibition further depends upon the rates achieved during cooling and rewarming. The minimal rate required to prevent any ice crystallization or recrystallization/devitrification in a given CPA is called the critical cooling rate (CCR) or critical warming rate (CWR), respectively. On the other hand, physical cracking is mainly related to thermomechanical stresses, which can be avoided by maintaining temperature differences below a critical threshold. In this simplified analysis, we calculate ΔT as the largest temperature difference occurring in a system during cooling or rewarming in the brittle/glassy phase. This ΔT is then used in a simple "thermal shock equation" to estimate thermal stress within the material to decide if the material is above the yield strength and to evaluate the potential for fracture failure. In this review we aimed to understand the limits of success and failure at different length scales for cryopreservation by vitrification, due to both ice crystallization and cracking. Here we use thermal modeling to help us understand the magnitude and trajectory of these challenges as we scale the biomaterial volume for a given CPA from the milliliter to liter scale. First, we solved the governing heat transfer equations in a cylindrical geometry for three common vitrification cocktails (i. e., VS55, DP6, and M22) to estimate the cooling and warming rates during convective cooling and warming and nanowarming (volumetric heating). Second, we estimated the temperature difference (ΔT) an d compared it to a tolerable threshold ( ΔTmax) based on a simplified "thermal shock" equation for the same cooling and rewarming conditions . We found, not surprisingly, that M22 achieves vitrification more easily during convective cooling and rewarming for all volumes compared to VS55 or DP6 due to its considerably lower CCR and CWR. Further, convective rewarming (boundary rewarming) leads to larger temperature differences and smaller rates compared to nanowarming (volumetric rewarming) for all CPAs with increasing failure at larger volumes. We conclude that as more and larger systems are vitrified and rewarmed with standard CPA cocktails, this work can serve as a practical guide to successful implementation based on the characteristic length (volume/surface area) of the system and the specific conditions of cooling and warming.

Critical rates of climate warming and abrupt collapse of ecosystems

In the age of climate warming, comprehension of ecosystems’ future is one of the pressing challenges to humanity. While most studies on climate warming focus on the ‘magnitude of change’ of the Earth’s temperature, the ‘rate’ at which it is increasing cannot be ruled out. Rapid warming has already caused sudden ecosystem transitions at numerous biodiversity hot spots; a mechanistic understanding of such transitions is crucial. Here, we study a slow–fast consumer–resource ecosystem interacting in rapid warming scenarios. Employing geometric singular perturbation theory, we find that while a gradual change in mean temperature may accord population persistence, a critical warming rate can drive the resource’s sudden collapse, termed a warming-induced abrupt transition. This further triggers the bottom-up effect, resulting in the extinction of the consumer. The difference between the optimum temperature of the resource’s growth rate and the habitat temperature is crucial in deciding the critical rate of warming. Consequently, species inhabiting extreme temperature regions are more susceptible to warming-induced collapse than those within intermediate temperature ranges. We find that stochastic fluctuations in the system can advance warming-induced transitions, and the efficacy of generic early warning signals to anticipate sudden transitions is challenged.

Nanowarming using Au-tipped Co35Fe65 ferromagnetic nanowires.

Ferromagnetic Co35Fe65, Fe, Co, and Ni nanowires have high saturation magnetizations (Ms) and magnetic anisotropies, making them ideal for magnetic heating in an alternating magnetic field (AMF). Here, Au-tipped nanowires were coated with polyethylene glycol (PEG) and specific absorption rates (SAR) were measured in glycerol. SAR increased when using metals with increasing Ms (Co35Fe65 > Fe > Co > Ni), reaching 1610 ± 20 W g-1 metal at 1 mg metal per ml glycerol for Co35Fe65 nanowires using 190 kHz and 20 kA m-1. Aligning these nanowires parallel to the AMF increased SAR up to 2010 W g-1 Co35Fe65. Next, Co35Fe65 nanowires were used to nanowarm vitrified VS55, a common cryoprotective agent (CPA).Nanowarming rates up to 1000 °C min-1 (5 mg Co35Fe65 per ml VS55) were achieved, which is 20× faster than the critical warming rate (50 °C min-1) for VS55 and other common CPAs. Human dermal fibroblast cells exposed to VS55, and Co35Fe65 nanowire concentrations of 0, 1 and 2.5 mg Fe per ml all showed similar cell viability, indicating that the nanowires had minimal cytotoxicity. With the ability to provide rapid and uniform heating, ferromagnetic nanowires have excellent potential for nanowarming cryopreserved tissues.

Ultrarapid Inductive Rewarming of Vitrified Biomaterials with Thin Metal Forms

Arteries with 1-mm thick walls can be successfully vitrified by loading cryoprotective agents (CPAs) such as VS55 (8.4 M) or less concentrated DP6 (6 M) and cooling at or beyond their critical cooling rates of 2.5 and 40 °C/min, respectively. Successful warming from this vitrified state, however, can be challenging. For example, convective warming by simple warm-bath immersion achieves 70 °C/min, which is faster than VS55’s critical warming rate of 55 °C/min, but remains far below that of DP6 (185 °C/min). Here we present a new method that can dramatically increase the warming rates within either a solution or tissue by inductively warming commercially available metal components placed within solutions or in proximity to tissues with non-invasive radiofrequency fields (360 kHz, 20 kA/m). Directly measured warming rates within solutions exceeded 1000 °C/min with specific absorption rates (W/g) of 100, 450 and 1000 for copper foam, aluminum foil, and nitinol mesh, respectively. As proof of principle, a carotid artery diffusively loaded with VS55 and DP6 CPA was successfully warmed with high viability using aluminum foil, while standard convection failed for the DP6 loaded tissue. Modeling suggests this approach can improve warming in tissues up to 4-mm thick where diffusive loading of CPA may be incomplete. Finally, this technology is not dependent on the size of the system and should therefore scale up where convection cannot.

Vitrification Assessment: Thermal Analysis of Cryoprotective Aqueous Solutions 1,2 Propanediol and Ethylene Glycol.

Cryopreservation of viable cells and cell materials is being developed for biological and biopharmaceutical applications. The inhibition of ice formation during the cooling and warming phase of vitrified living biological samples is important for their survival. The tendency to form glasses (glass transition temperature, Tg) upon cooling in the vitrification solution and the stability of the amorphous state upon warming to determine the critical cooling rate (Vccr) and critical warming rates (Vcwr) are evaluated. The study of thermal properties of ethylene glycol (EG) and 1,2-propanediol (PD) solutions were performed to improve vitrification through better understanding of their molecular mobility and viscosity. Two sets of aqueous solutions were tested. In group A, 35% EG (w/w) was added to different PD concentrations (5%, 10%, and 15%). In group B, 20% PD (w/w) was combined with varying concentrations of EG (20%, 24%, 27%, and 30%). Using the semiempirical model of Boutron, the values of Vccr and Vcwr for group A were 10, 8, <2.5°C/min, and 1.65 × 105, 678, 32°C/min, respectively. For group B, the values were 24, 10, <2.5, <2.5°C/min, and 9.5 × 103, 144, 48, 7°C/min, respectively. While the values of Vccr and Vcwr for 40% EG were 123 and 8.84 × 105°C/min, respectively. The methyl group in PD enhanced the vitreous state, lowering the melting point. Adding a small concentration of PD (3%) to VM3 vitrification solution improved and increased the Tg and enhanced their thermal stability. Analyzing the thermal properties of cryoprotectant is useful when designing the cryopreservation protocols.

Vitrification tendency and stability of DP6-based vitrification solutions for complex tissue cryopreservation

Vitrification tendency and stability of the amorphous state were analyzed by means of differential scanning calorimetry (DSC) for the vitrification solution DP6, with and without additional solutes to enhance ice suppression. This study is a part of an ongoing research effort to characterize the thermophysical and mechanical properties of DP6 and its derivatives, and their qualities as cryoprotective solutions. DP6 was determined to have a critical cooling rate necessary to ensure vitrification of 2.7 °C/min. The following additional solutions were tested: DP6 + 6% (2R, 3R) 2,3-butanediol, DP6 + 6% 1,3-cyclohexanediol, DP6 + 6% (0.175M) sucrose, DP6 + 12% PEG 400, and DP6 + 17.1% (0.5 M) sucrose. The additives decreased the critical cooling rate of the DP6 solution to rates below 1 °C/min that were not quantifiable by the DSC techniques used. The following critical warming rates necessary to avoid devitrification were identified for DP6 and the modified solutions, respectively: 189 °C/min, 5 °C/min, ≈ 1 °C/min, 15 °C/min, <1 °C/min, and <1 °C/min. Glass transition temperatures and melting temperatures were also measured. Sucrose was the least effective additive on a per mass basis, with 1,3-cyclohexanediol appearing to be the most effective additive for suppressing ice formation in DP6.

134 Fundamentals of ice formation during rapid cooling and warming

We have examined ice formation in aqueous solutions containing common cryoprotectants during cooling and warming at rates from ∼10 K/s to >10,000 K/s. For all solutes tested, the critical cooling rate below which ice forms varies exponentially with solute concentration. The exponential’s characteristic concentration for each solute correlates with the solute’s Stokes radius. We have developed a simple statistical mechanical extension of classical nucleation theory that assumes solutes must be excluded from the critical nucleus. This theory provides an excellent account of our data, and relates the characteristic concentration for each solute to the solute radius and the critical nucleation radius of ice in pure water. This microscopic theory of glass formation in the presence of solutes has consequences for cryobiology, for cloud physics, and for general glass forming systems. Ice formation on warming is of comparable or greater importance to ice formation on cooling in determining survival of cryopreserved samples. Measurements of solutions of several common cryoprotectants show that the critical warming rates below which ice transiently forms on warming are typically one to three orders of magnitude larger than critical cooling rates. Critical warming rates also depend upon cooling rates, due to the presence of small ice fractions in nominally vitrified samples. Current phenomenological models of ice nucleation and growth with current best estimates for their input parameters derived from data at large concentrations and small cooling rates overestimate both critical warming rates and critical cooling rates by orders of magnitude in the low concentration, high rate regime. In vitrification protocols, minimizing concentrations of potentially damaging cryoprotectants while minimizing ice formation thus requires ultrafast warming rates as well as fast cooling rates to minimize the required warming rates. Source of funding: NIH, NSF. Conflict of interest: None declared. ret6@cornell.edu

Effect of common cryoprotectants on critical warming rates and ice formation in aqueous solutions

Ice formation on warming is of comparable or greater importance to ice formation on cooling in determining survival of cryopreserved samples. Critical warming rates required for ice-free warming of vitrified aqueous solutions of glycerol, dimethyl sulfoxide, ethylene glycol, polyethylene glycol 200 and sucrose have been measured for warming rates of order 10–104K/s. Critical warming rates are typically one to three orders of magnitude larger than critical cooling rates. Warming rates vary strongly with cooling rates, perhaps due to the presence of small ice fractions in nominally vitrified samples. Critical warming and cooling rate data spanning orders of magnitude in rates provide rigorous tests of ice nucleation and growth models and their assumed input parameters. Current models with current best estimates for input parameters provide a reasonable account of critical warming rates for glycerol solutions at high concentrations/low rates, but overestimate both critical warming and cooling rates by orders of magnitude at lower concentrations and larger rates. In vitrification protocols, minimizing concentrations of potentially damaging cryoprotectants while minimizing ice formation will require ultrafast warming rates, as well as fast cooling rates to minimize the required warming rates.

Vitrification Solutions for the Cryopreservation of Tissue-Engineered Bone

Vitrification solutions were explored for the cryopreservation of tissue-engineered bone constructs using differential scanning calorimetry, visual inspection, toxicity and viability assays. Two vitrification "cocktails" (VS55 and VEG; concentration range of 80–100%)—40% (vol/vol) DMSO and 40% (vol/vol) glycerol solutions—were studied with and without an ice blocker (IB). Results show that 95% VEG + IB solution is the best option to preserve the OB:HA scaffold-cell complex from the standpoint of critical cooling rate (5°C/min), critical warming rate (35°C/min), minimal scaffold damage, toxicity, and preliminary cryopreservation results (92.0% ± 1.4% for suspended cells, 43.0% ± 2.7% for attached cells). Ice blocker was found to reduce the critical warming rates of VS55 and VEG solutions at higher concentrations but worsen devitrification of lower concentration solutions. The fact that the critical cooling and warming rates are larger for larger systems as judged by visual inspection indicates that visual inspection is a reasonable practical guide to determine the critical cooling and warming rates for larger volume solutions, especially with embedded HA samples. Fracture of vitrified solutions is detrimental to cells, but such fracture should be avoidable by slow and uniform cooling combined with a minimum storage temperature just below the glass transition temperature rather than lower temperatures.

Thermal properties of ethylene glycol aqueous solutions*1

Preventing ice crystallization by transforming liquids into an amorphous state, vitrification can be considered as the most suitable technique allowing complex tissues, and organs cryopreservation. This process requires the use of rapid cooling rates in the presence of cryoprotective solutions highly concentrated in antifreeze compounds, such as polyalcohols. Many of them have already been intensively studied. Their glass forming tendency and the stability of their amorphous state would make vitrification a reality if their biological toxicity did not reduce their usable concentrations often below the concentrations necessary to vitrify organs under achievable thermal conditions. Fortunately, it has been shown that mixtures of cryoprotectants tend to reduce the global toxicity of cryoprotective solutions and various efficient combinations have been proposed containing ethanediol. This work reports on the thermal properties of aqueous solutions with 40, 43, 45, 48, and 50% (w/w) of this compound measured by differential scanning calorimetry. The glass forming tendency and the stability of the amorphous state are evaluated as a function of concentration. They are given by the critical cooling rates v ccr above which ice crystallization is avoided, and the critical warming rates v cwr necessary to prevent ice crystallization in the supercooled liquid state during rewarming. Those critical rates are calculated using the same semi-empirical model as previously. This work shows a strong decrease of averaged critical cooling and warming rates when ethanediol concentration increases, V ccr =569 and V cwr =1.08×10 10 K/min for 40% (w/w) whereas V ccr =11 and V cwr =853 K/min for 50% (w/w). Those results are compared with the corresponding properties of other dialcohols obtained by the same method. Ethylene glycol efficiency is between those of 1,2-propanediol and 1,3-propanediol.

Thermal properties of ethylene glycol aqueous solutions

Preventing ice crystallization by transforming liquids into an amorphous state, vitrification can be considered as the most suitable technique allowing complex tissues, and organs cryopreservation. This process requires the use of rapid cooling rates in the presence of cryoprotective solutions highly concentrated in antifreeze compounds, such as polyalcohols. Many of them have already been intensively studied. Their glass forming tendency and the stability of their amorphous state would make vitrification a reality if their biological toxicity did not reduce their usable concentrations often below the concentrations necessary to vitrify organs under achievable thermal conditions. Fortunately, it has been shown that mixtures of cryoprotectants tend to reduce the global toxicity of cryoprotective solutions and various efficient combinations have been proposed containing ethanediol. This work reports on the thermal properties of aqueous solutions with 40, 43, 45, 48, and 50% (w/w) of this compound measured by differential scanning calorimetry. The glass forming tendency and the stability of the amorphous state are evaluated as a function of concentration. They are given by the critical cooling rates v ccr above which ice crystallization is avoided, and the critical warming rates v cwr necessary to prevent ice crystallization in the supercooled liquid state during rewarming. Those critical rates are calculated using the same semi-empirical model as previously. This work shows a strong decrease of averaged critical cooling and warming rates when ethanediol concentration increases, V ccr=569 and V cwr=1.08×10 10 K/min for 40% (w/w) whereas V ccr=11 and V cwr=853 K/min for 50% (w/w). Those results are compared with the corresponding properties of other dialcohols obtained by the same method. Ethylene glycol efficiency is between those of 1,2-propanediol and 1,3-propanediol.

A Theoretical Model of Intracellular Devitrification

Devitrification of the intracellular solution can cause significant damage during warming of cells cryopreserved by freezing or vitrification. Whereas previous theoretical investigations of devitrification have not considered the effect of cell dehydration on intracellular ice formation, a new model which couples membrane-limited water transport equations, classical nucleation theory, and diffusion-limited crystal growth theory is presented. The model was used to explore the role of cell dehydration in devitrification of human keratinocytes frozen in the presence of glycerol. Numerical simulations demonstrated that water transport during cooling affects subsequent intracellular ice formation during warming, correctly predicting observations that critical warming rate increases with increasing cooling rate. However, for cells with a membrane transport activation energy less than approximately 50 kJ/mol, devitrification was also affected by cell dehydration during warming, leading to a reversal of the relationship between cooling rate and critical warming rate. Thus, for low warming rates (less than 10°C/min for keratinocytes), the size and total volume fraction of intracellular ice crystals forming during warming decreased with decreasing warming rate, and the critical warming rate decreased with increasing cooling rate. The effects of water transport on the kinetics of intracellular nucleation and crystal growth were elucidated by comparison of simulations of cell warming with simulations of devitrification in H2O-NaCl-glycerol droplets of constant size and composition. These studies showed that the rate of intracellular nucleation was less sensitive to cell dehydration than was the crystal growth rate. The theoretical methods presented may be of use for the design and optimization of freeze-thaw protocols.

Effects of Solute Methoxylation on Glass-Forming Ability and Stability of Vitrification Solutions

The effects of replacing hydroxyl groups with methoxyl (OCH3) groups in the polyols ethylene glycol (EG), propylene glycol (PG), glycerol, and threitol were studied by differential scanning calorimetry (DSC) during cooling of aqueous solutions to −150°C and subsequent rewarming. For 35% (w/w) PG, 40% EG, and 45% glycerol, a single substitution of a terminal hydroxyl group with a methoxyl group reduced the critical cooling rate necessary to avoid ice on cooling (vitrify) from approximately 500 to 50°C/min. This reduction was approximately equivalent to increasing the parent polyol concentration by 5% (w/w). The critical warming rate calculated to avoid formation of ice on rewarming (devitrification) was also reduced by methoxyl substitution, typically by a factor of 104 for dilute solutions. Double methoxylation (replacement of both terminal hydroxyls) tended to result in hydrate formation, making these compounds less interesting. An exception was threitol, for which substituting both terminal hydroxyls by methoxyls reduced the critical rewarming rate of a 50% solution by a factor of 107 without any hydrate formation. These glass-forming and stability properties of methoxylated compounds, combined with their low viscosity, enhanced permeability, and high glass transition temperatures, make them interesting candidate cryoprotective agents for cryopreservation by vitrification or freezing.

Critical Cooling and Warming Rates to Avoid Ice Crystallization in Small Pieces of Mammalian Organs Permeated with Cryoprotective Agents

Measurements were made by differential scanning calorimetry on small pieces of rabbit kidney permeated with 2,3-butanediol containing mainly the levo- and dextro-isomers. The critical cooling rates necessary to vitrify the pieces of organ, and the corresponding critical warming rates which are required to avoid crystallization in the vitrified samples, were determined. The dynamic method used for these determinations is described. The glass-forming tendency and the stability of the amorphous state were both greater in the kidney tissue samples than in the bulk cryoprotective solution. This result is discussed in the context of the lowering of the freezing point of water in emulsions and the promotion of supercooling in hydrogels and porous materials. In corresponding experiments with rat hearts impregnated with 1,2-propanediol, only the critical warming rate was reduced.

Theoretical Prediction of Vitrification and Devitrification Tendencies for Cryoprotective Solutions

Based on Boutron's semi-empirical crystallization theory, exact analytical expressions for variation in the quantity of ice crystallized have been obtained by the integral method without using finite expansions. With the aid of the experimental data from DSC, these expressions can be used to calculate the critical cooling rates required for vitrification and the critical warming rates necessary to avoid devitrification, thereby predicting the glass-forming tendency and the stability of the amorphous state for cryoprotective agents (CPAs), respectively. It is shown that an aqueous solution of l-2, 3-butanediol has the highest glass-forming tendency and the most stable wholly amorphous state, followed by 1, 2-propanediol and DMSO, ethylene glycol, and glycerol. It is also found that the high polymers have obvious non-Arrhenius properties. Therefore, the stability of the CPAs can be enhanced by adding PVP or PEG.

Nucleation and Crystal Growth in a Vitrification Solution Tested for Organ Cryopreservation by Vitrification

Nucleation and crystal growth are investigated for vitrification solution VS41A (dimethyl sulfoxide, formamide, and 1,2-propanediol) in an aqueous carrier solution giving, when added to these three cryoprotectants, a concentration of other solutes in the whole solution the same as that in Euro-Collins, with a 55% (w/v) cryoprotectant concentration. This concentration is assumed to achieve physical properties under 1 atmosphere similar to those of solution VS4 used under 1000 atmospheres. The thermal range and the kinetics of nucleation and crystal growth are investigated by DSC through different thermal treatments. It is found that the nucleation thermal range is below -90°C and that of crystal growth is above -85°C for a relatively long experimental time. The nucleation density is also studied through direct observations by cryomicroscopy and is related to the amount of crystallization calorimetrically recorded. The effect of storage below the glass transition shows the possibility of a slow increase in nucleation below the glass transition, as already observed by other authors for different aqueous solutions. Isothermal crystallization is analyzed within the Johnson-Mehl-Avrami model for temperatures above -75°C. The corresponding samples have been cooled and warmed at the same rate of 40°C/min and calculations give, at constant nuclei numbers, an activation energy of 9.3 ± 0.3 kcal/mol and the Avrami exponent n = 2.2 ± 0.05. This shows a two-dimensional crystal growth as observed by cryomicroscopy. The estimated critical warming rate relevant to the preservation of rabbit kidneys by vitrification is 270°C/min with or without an increase in the nucleus density during storage. The present results support the possibility of using VS4 solution for vitrification of rabbit kidneys if pressure is not a limiting factor.

Theoretical prediction of devitrification tendency: Determination of critical warming rates without using finite expansions

Previously, critical warming rates vcr above which ice did not have enough time to crystallize had been roughly evaluated for many wholly amorphous aqueous solutions. These evaluations were obtained by extrapolation of the linear variation of the devitrification temperature Td with log v, where v is the warming rate, observed experimentally between 2.5 and 80 °C/min, Theory also gives such a linear variation, but only using the first term of a finite expansion. The other terms can be neglected only for small variations of Td. These evaluations were sufficient for classification of the solutions, but large errors were made in vcr. A new and more accurate method of determination of the variation of Td with v is presented here. The general equation giving in our models the derivative of the quantity of ice formed versus temperature T is differentiated, instead of integrated using a finite expansion. This gives an explicit expression of v versus Td assuming that the ratio xd of the quantity of ice formed at Td to the total quantity of ice formed on warming is constant. Experimentally, xd is constant within a good approximation. Theoretical curves representing the variation of Td with v have been drawn for solutions of 35 or 45% (ww) 1,2-propanediol in water. Td never reaches the temperature of the end of melting Tm, but as v tends toward infinity, Td tends toward an asymptotic value of 0.96Tm for 35% solute. For that solution, above about 103 °C/min, Td deviates appreciably from linearity with log v, but 1Td remains almost linear with log v up to Td = 0.95Tm. Therefore, systematic comparison of the theoretical variation of Td with v with a linear variation of 1Td with log v has been done, varying the parameters of the equations within the entire experimental range. Similar conclusions can be given for all the solutions. Experimentally for Td = 0.95Tm, the quantity of ice crystallized is generally less than 0,1% of the solution, reaching 1% only once. Therefore, a new definition of the critical warming rate vcr has been used, corresponding to extrapolation of the linear variation of 1T with log v up to Td = 0.95Tm. New values of vcr have been calculated for all the binary systems previously studied. The order of the solutions is almost the same, but the new values of vcr are significantly smaller than the former.

Theoretical prediction of devitrification tendency—Determination of critical warming rates without using finite expansions

Theoretical prediction of devitrification tendency—Determination of critical warming rates without using finite expansions

Ternary systems with 1,2-propanediol—A new gain in the stability of the amorphous state in the system water-1,2-propanediol-1-propanol

Three ternary systems with water and 1,2-propanediol were investigated, where the third component is 1-propanol, ethanol, or glycerol. 1-Propanol and ethanol give hydrates in their aqueous solutions as well as in these ternary systems, while glycerol gives none. No gain in the stability of the amorphous state and glass-formation tendency is obtained, for the same water contents, when 1,2-propanediol is partially replaced by ethanol. The gain is negligible when it is partially replaced by glycerol. On the contrary, a large maximum in the stability of the amorphous state is obtained, with a critical warming rate dropping from 10 8 to 10 4 °C/min in the presence of 65% (w/w) water when 15% (w/w) of the 1,2-propanediol is replaced by 1-propanol. The decrease in the glass formation tendency due to this replacement and corresponding to a few hydrate crystallization is small. Not only the higher stability of the amorphous state, but also in some cases the replacement of ice crystallization by clathrate crystallization at lower temperatures could perhaps contribute to a better cryoprotection of cells for some cooling and warming rates. The similarities observed between the ternary systems investigated gives an idea of the general behaviour of these systems