Effect of Moisture Sorption On Free Volume and Relaxation of Spray Dried Dispersions: Relation to Drug Recrystallization

Document Type


Publication Date



Mathematics and Natural Sciences


The effect of vapor sorption on the free volume of drug-polymer spray dried dispersions (SDDs) was investigated, along with the crystallization propensity of drug molecules in SDDs after exposure to humidity. Subsequently, the correlation of free volume change and relaxation time with drug recrystallization was examined. Four polymers, including polyvinylpyrrolidone (PVP], polyvinylpyrrolidone vinyl acetate copolymer (PVPVA], hydroxypropyl cellulose (HPC] and hydroxypropyl methylcellulose acetate succinate (HPMCAS), and two drugs (indomethacin and ketoconazole) were selected for preparing SDDs. Free volume data of the exposed SDDs were obtained with positron annihilation lifetime spectroscopy (PALS) while the relaxation time was measured using a TA rheometer. Additionally, the crystallization propensity of APIs in the exposed SDDs was assessed using both polarized light microscopy (PLM) and powder X-ray diffraction (PXRD), followed by relating API crystallization inclination with expansion of holes and relaxation time. Finally, Cohen and Turnbull molecular transport model, along with its extensions by Vrentas and Duda, was qualitatively utilized for interpreting the recrystallization propensity of API molecules. In conclusion, API recrystallization is closely related to free volume change upon moisture sorption and relaxation time, but system dependent; overall, drug-HPMC-AS SDDs appear physically stable against recrystallization due to less increase in free volume.


Polymers and High Performance Materials

Publication Title

Journal of Pharmaceutical Sciences

Find in your library