Effect of freeze-drying process conditions on the stability of nanoparticles

The purpose of this study was to optimize the freeze-drying processes of nanoparticles in order to improve their end-used properties and their stability. Polycaprolactone (PCL) nanoparticles were prepared by the emulsification-diffusion method and then were frozen at different freezing rates. Finally, the nanoparticles were freeze-dried under different operating conditions by using a laboratory-made freeze-dryer. Then, the average particle size was analyzed by using a Coulter((R)) LS 230 apparatus firstly after the freezing step and finally after the sublimation step. The surface morphology and the thermophysical characteristics of the nanoparticles were determined by SEM and by DSC, respectively. It was observed that, the freezing process can break the nanoparticles and cause the leakage of their contents during the freeze-drying step. The higher the freezing rate, the larger the size of nanoparticles during the freezing process. From the results DSC data, it could be assumed that the nanoparticles in the nanosuspensions may have been broken not by water crystallization in the external phase, but by the solidification of the oil (miglyol) in the internal phase.