A quantitative analysis of the thermal properties of porcine liver with glycerol at subzero and cryogenic temperatures.

There is a lack of information on the effect of cryoprotective agents (CPAs) on the thermal properties of biomaterials at cryobiologically relevant temperatures (i.e. <233.15K, -40 degrees C). Thermal properties that are of most interest include: thermal conductivity, density, specific heat, and latent heat resulting from phase change in tissue systems. Availability of such information would be beneficial for accurate mathematical modeling of cryobiological applications. Recently, we reported these thermal properties in phosphate buffered saline (PBS) with varying concentrations of glycerol, a widely used cryoprotective agent. In this study we extend these results by assessing the effects of glycerol on the thermal properties of porcine liver at subzero temperatures. Differential scanning calorimeter (DSC) was used to measure the specific heat and the latent heat release of porcine liver immersed in PBS and varying concentrations of glycerol. The specific heat data obtained from the DSC experiments were also used to predict the bulk thermal conductivity. This was done using a transient heat transfer model with a thermistor probe technique. Results show that the introduction of glycerol significantly alters thermal properties from known values for H2O and non-treated liver. Therefore, inaccuracies in thermal predictions can be expected due to the application of measured vs. predicted thermal properties such as from weight averaging. This supports the need for these and other measurements of biomaterial thermal properties, with and without CPA addition, in the cryogenic regime.