Revealing isochoric water nucleation: a visual study.

The phenomena of water freezing at constant volume, or isochoric, is becoming more and more fascinating. However, because the system is subjected to extremely high pressures, it is exceedingly challenging to investigate it visually. Fewer properties have been found visually up till now, but many have been found through other means. Nevertheless, we were able to design a reactor so that it could be observed through a microscope as water was frozen and thawed at constant volume, reaching temperatures as low as - 12 °C and pressures up to 129 MPa. In this study, we observed critical characteristics visually, focusing on the location of the ice nucleus, its shape, and dynamics. Phase transitions from liquid to solid state are essential mechanisms in the physical sciences. The creation of ice stands as the quintessential and pervasive example of nucleation, playing a central role in diverse disciplines such as geology, biology, aviation, and climate research.

Preservation of black grapes by isochoric freezing.

Fruits are perishable. It's crucial to have an efficient preservation technique that may extend storage duration while maintaining the physical quality and nutritional values to avoid wastage. The majority of long-term storage solutions for fruits use refrigeration. In this study, we evaluate the potential of isochoric freezing as an alternative method of preservation for black grapes (Vitis vinifera L.). We compare the properties of black grapes preserved for 7 days in trehalose solution at -4 °C in isochoric conditions (average pressure 34.2 MPa) with those of fresh black grapes and with grapes preserved isobarically in four conditions (room temperature, in the fridge, in the freezer, and in a plastic bag filled with trehalose solution). The results indicate that grapes preserved by isochoric freezing at temperatures below the freezing point of water do not lose weight; on the contrary, they resulted in a very small (2%) weight gain. Freezing under isochoric conditions did not result in significant changes in terms of macroscopic appearance, colour, firmness, °Brix values, or pH. We consider that isochoric freezing has the potential to be used as a preservation method for grapes while maintaining physicochemical parameters similar to those of fresh fruits.

Temperature-pressure correlations of cryoprotective additives for the design of constant volume cryopreservation protocols.

In the recent years, the use of constant volume (isochoric) cryopreservation, in medicine and biotechnology has captured more attention from the research community and now there is an increasing interest in the use of this new technology. It has been established that the thermodynamics of isochoric freezing is different from that of isobaric (constant pressure) freezing. This study provides researchers in the field experimental results for various compositions of cryoprotectants commonly used in isobaric cryopreservation, in terms of temperature-pressure-molar concentration correlation. It also reveals experimental isochoric thermodynamic data for the following cryoprotectants, commonly used in isobaric cryopreservation: dimethyl sulfoxide, trehalose, ethylene glycol and diethylene glycol. Currently, the data on the pressure-temperature correlation in an isochoric system of cryoprotectants used in isobaric cryopreservation is not available. Our new experimental results indicate that the studied concentrations for each of the CPAs, lower and expands the range of temperatures in which cryopreservation by isochoric freezing can be safely practiced. We consider that these experiments will aid researchers developing new isochoric cryopreservation protocols.

Glucose and glycerol temperature-pressure correlations for the design of cryopreservation protocols in an isochoric system at subfreezing temperature.

There is growing interest in the use of isochoric (constant volume) freezing for cryopreservation of biological matter. The goal of this study is to generate fundamental experimental data on the pressure temperature relation during the freezing of an isochoric system of aqueous solutions of two compounds, glucose and glycerol. Glucose and glycerol are commonly used as cryoprotectants in conventional isobaric (constant pressure) cryopreservation protocols. Earlier studies have shown that the increase in pressure during isochoric freezing is detrimental to biological matter and limits the range of temperatures in which isochoric freezing can be used for preservation to temperatures corresponding to pressures below 40 MPa. In physiological saline solution this pressure corresponds to a temperature of - 4 °C. Our new experimental data shows that the addition of 2 M glycerol to the saline solution lowers the temperature at which the isochoric freezing pressure is 40 MPa to -11 °C, 3 M glycerol to - 16.5 °C, and 4 M glycerol to - 24.5 °C, thereby substantially expending the range of temperatures in which cryopreservation by isochoric freezing can be practiced.