LAUSR

The physical and chemical stability of various biorelevant media (FaSSGF, FaSSIF V1, FaSSIF V2, FaSSIF V3, and FeSSIF) were investigated over periods after preparation of up to 120 h at room temperature (RT) (22 °C) and 37 °C. It was shown that biorelevant instant powders are not a source of microbiological contamination. It was also established that the physical characteristics of FaSSGF and FeSSIF are invariant with time, so they can be used immediately after preparation, i.e., without any equilibration time. Alternatively, they can be stored for up to 96 h at RT before use. By contrast, FaSSIF V1 requires an equilibration time of 2 h, and FaSSIF V2 requires an equilibration time of 24 h to enable the media characteristics to stabilize. After this equilibration time, both FaSSIF V1 and V2 can also be stored for at least up to 96 h at RT prior to use; longer storage times have not yet been tested. The particle size of FaSSIF V3 appears to continually evolve over time. For FaSSIF V3, it is thus recommended that the waiting period between preparation and use be standardized among experiments. Additionally, the colloidal particle structures present in the various FaSSIF versions were analyzed by cryogenic transmission electron microscopy (Cryo-TEM). Various kinds of micelles (globular, disc, multilayer disc, and thread-like micelles) were observed in all samples, and some samples also contained unilamellar vesicles. Differences in solubility of drugs among the various FaSSIF versions can be partly explained by the results from Cryo-TEM.