Study on redispersibility of drug nanocrystals particles during storage: Novel understanding based on water adsorption and glass transition of amorphous matrix formers

The objective of this study was to understand the influence of the water adsorption and glass transition of matrix formers on redispersibility in water of drug nanocrystals-aggregated particles(NAP) during storage, and the critical storage strategy for NAP powders were determined based on the Guggenheim-Anderson-de Boer (GAB) and the Gordon-Taylor models. Apigenin was used as model drug. Six kinds of matrix formers sucrose(SU), lactose(LA), trehalose(TR), inulin(IN), maltodextrin(MA) and PVPK30(PV) were used to prepare apigenin nanocrystals-aggregated particles (AN-NAPs). The results demonstrated that the adsorption isotherms curves of six kinds of matrix formers based AN-NAPs all showed typical II (S) type adsorption. The water activity significantly influenced the redispersibility of AN-NAP, which could be attributed to the microstructure collapse of amorphous matrix induced by moisture adsorption at high water activity or high moisture. MD based AN-NAP(AN-NAP/MD) exhibited much better redispersibility at high water activity(0.689) compared with the other amorphous matrix formers. MD was able to significantly enlarge the Tg of AN-NAP system and prevent from aggregation of AN-NAP compared to other matrix formers. And the critical water activity and moisture content of AN-NAPs were in the ranges of 0.015-0.545 and 0.0412-0.1508 g water/g dry matter, respectively. Of all amorphous matrix based NAPs, the critical water activity of AN-NAP/MD was the highest (0.545), and the critical moisture content was 0.1003 g water/g dry matter, and followed by TR based on AN-NAP. MD could be used as an excellent matrix former for nanocrystals-aggregated particles during storage. Therefore, the roles of water adsorption and glass transition of matrix formers on redispersibility of drug nanocrystals-aggregated particles during storage was successful elucidated, and the critical storage strategy was proposed based on the GAB model and the Gordon-Taylor model.