Effect of a high-pressure-induced freezing process on the stability of freeze-dried nanocapsules

The objective of this study was to develop a freeze-drying process involving high-pressure techniques during freezing in order to optimize the stability of nanocapsules. Nanocapsules prepared by the emulsion-diffusion method were frozen at -20,-10, and -5 degrees C, respectively, and dried under vacuum as a conventional freeze drying (CFd). For the high-pressure freezing process, the nanocapsules suspensions were frozen at -20,-10, and -5 degrees C at 100, 200, and 300MPa, respectively, and then dried under vacuum conditions (abbreviated as HPFd). The size and morphological analysis of freeze-dried samples were investigated by using Mastersizer((R)), TEM, and SEM. From these experiments, the mean nanocapsules sizes were entirely aggregated depending on increasing pressure and decreasing freezing temperature in CFd. In HPFd, the nanocapsules frozen at -10 degrees C were stable depending on the increment of the pressure level. We concluded that the HPFd process was more effective for the stability of nanocapsules compared to the CFd process at freezing temperatures of -10 degrees C due to high supercooling of the internal phase during the high-pressure freezing process.