Large Thermal Conductivity Differences between the Crystalline and Vitrified States of DMSO with Applications to Cryopreservation.

<p>Thermal conductivity of dimethyl-sulfoxide (DMSO) solution is measured in this study using a transient hot wire technique, where DMSO is a key ingredient in many cryoprotective agent (CPA) cocktails. Characterization of thermal properties of cryoprotective agents is essential to the analysis of cryopreservation processes, either when evaluating experimental data or for the design of new protocols. Also presented are reference measurements of thermal conductivity for pure water ice and glycerol. The thermal conductivity measurement setup is integrated into the experimentation stage of a scanning cryomacroscope apparatus, which facilitates the correlation of measured data with visualization of physical events. Thermal conductivity measurements were conducted for a DMSO concentration range of 2M and 10M, in a temperature range of -180°C and 25°C. Vitrified samples showed decreased thermal conductivity with decreasing temperature, while crystalline samples showed increased thermal conductivity with decreasing temperature. These different behaviors result in up to a tenfold difference in thermal conductivity at -180°C. Such dramatic differences can drastically impact heat transfer during cryopreservation and their quantification is therefore critical to cryobiology.</p

Best-fit polynomial approximation data for the thermal conductivity curves displayed in Fig 7.

<p>* A dataset consisting of fewer than ten data points</p><p>Best-fit polynomial approximation data for the thermal conductivity curves displayed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125862#pone.0125862.g007" target="_blank">Fig 7</a>.</p

Solid fraction during solidification of a water-DMSO mixture, extracted from a phase diagram [13].

<p>Solid fraction during solidification of a water-DMSO mixture, extracted from a phase diagram [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125862#pone.0125862.ref013" target="_blank">13</a>].</p

Thermal conductivity as a function of solid fraction for DMSO at various concentrations, where the Bruggeman model is calculated with Eq (7) for 6M DMSO.

<p>Thermal conductivity as a function of solid fraction for DMSO at various concentrations, where the Bruggeman model is calculated with Eq (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125862#pone.0125862.e007" target="_blank">7</a>) for 6M DMSO.</p

Temperature measurements during thermal conductivity experiments: (a) temperature results of three consecutive thermal experiments, where the change in the bulk sample temperature is best-fitted with a 2^nd order polynomial; (b) a higher magnification of an experimental dataset; and (c) a temperature dataset used to calculate the thermal conductivity after the subtraction of the bulk sample rewarming curve, where the slope of the best-fitted curve on a semi-log plot is used to calculate the thermal conductivity (shown as a solid line in figure).

<p>Temperature measurements during thermal conductivity experiments: (a) temperature results of three consecutive thermal experiments, where the change in the bulk sample temperature is best-fitted with a 2^nd order polynomial; (b) a higher magnification of an experimental dataset; and (c) a temperature dataset used to calculate the thermal conductivity after the subtraction of the bulk sample rewarming curve, where the slope of the best-fitted curve on a semi-log plot is used to calculate the thermal conductivity (shown as a solid line in figure).</p

Schematic illustration of (a) the cryomacroscope experimentation stage (the red arrow represents the direction of view), and (b) the hot wire sensor setup in the cuvette (sample container).

<p>Schematic illustration of (a) the cryomacroscope experimentation stage (the red arrow represents the direction of view), and (b) the hot wire sensor setup in the cuvette (sample container).</p

Schematic illustration of the scanning cryomacroscope setup and peripheral instrumentation [11]; the modified experimentation stage for thermal conductivity measurements is displayed with more detail in Fig 2.

<p>Schematic illustration of the scanning cryomacroscope setup and peripheral instrumentation [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125862#pone.0125862.ref011" target="_blank">11</a>]; the modified experimentation stage for thermal conductivity measurements is displayed with more detail in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125862#pone.0125862.g002" target="_blank">Fig 2</a>.</p

Cryomacroscope images of samples in various states: (a) a vitrified 7.05M DMSO sample at a temperature of -147°C; (b) a 2M DMSO sample undergoing crystallization in the form of dendrites at temperature of -10°C; (c) a partially crystallized 6M DMSO sample at a temperature of -58°C; and (d) a completely crystallized 6M DMSO solution at a temperature of -65°C.

<p>Cryomacroscope images of samples in various states: (a) a vitrified 7.05M DMSO sample at a temperature of -147°C; (b) a 2M DMSO sample undergoing crystallization in the form of dendrites at temperature of -10°C; (c) a partially crystallized 6M DMSO sample at a temperature of -58°C; and (d) a completely crystallized 6M DMSO solution at a temperature of -65°C.</p

The liquidus temperature, <i>T</i>_<i>l</i>, and the solidus temperature, <i>T</i>_<i>s</i>, of solution concentrations observed to vitrify in this study, from a water-DMSO phase diagram [9].

<p>The liquidus temperature, <i>T</i>_<i>l</i>, and the solidus temperature, <i>T</i>_<i>s</i>, of solution concentrations observed to vitrify in this study, from a water-DMSO phase diagram [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125862#pone.0125862.ref009" target="_blank">9</a>].</p

The temperature of melting completion based on experimental results, <i>T</i>_<i>m</i>, observed during thermal conductivity measurements in comparison with the liquidus temperature, <i>T</i>_<i>l</i>, from a water-DMSO phase diagram [9].

<p>* No definite observation could be made</p><p>‡ Uncertainty only due to extraction of data from the phase diagram in [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125862#pone.0125862.ref009" target="_blank">9</a>]</p><p>† Uncertainty only due to temperature measurements in the current study</p><p>The temperature of melting completion based on experimental results, <i>T</i>_<i>m</i>, observed during thermal conductivity measurements in comparison with the liquidus temperature, <i>T</i>_<i>l</i>, from a water-DMSO phase diagram [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0125862#pone.0125862.ref009" target="_blank">9</a>].</p