Phase Change Behavior of Biomedically Relevant Solutions

Understanding the phase change behavior of biomedically relevant solutions is critical to the development of cryopreservation and cryosurgery protocols. In the present study, the phase change characteristics, particularly thermodynamically non-equilibrium phenomena including supercooled ice nucleation and eutectic formation, of various compositions and concentrations of biological solutions with/without glycerol as a cryoprotective agent (CPA) were investigated using a differential scanning calorimeter (DSC) and cryomicroscopy. The eutectic transitions (crystallization and melting) were observed in not only water-NaCl binary solutions, but also phosphate buffered saline (PBS) solutions. The eutectic transitions in both water-NaCl and PBS solutions were depressed during freezing far below their thermodynamic equilibrium eutectic temperatures. Contrary to freezing, eutectic melting starts very close to the thermodynamic equilibrium eutectic temperature during thawing. However, the eutectic transitions disappeared when a small amount of glycerol (∼0.1M) was added.