Roles of cryo/thermal strength for redispersibility of drug nanocrystals: a representative study with andrographolide

Due to limited understanding about the effect of cryo/thermal strength from drying process on the redispersibility of drug nanocrystals, the impact of the different type and concentration of stabilizers and matrix formers on the redispersibility of nanocrystals were systematically investigated. Andro nanosuspensions were transformed into Andro nanocrystals (Andro-NC) via different drying process. The results demonstrated that the redispersibility of Andro-NC at the aggressive cryo-strength (meant higher freezing rate) was more excellent than those at conservative and moderate condition. Compared to the thermal stress from drying, the employed amount and type of stabilizers more dramatically affected the redispersibility of Andro-NCP during lyophilization. The HPMC-sucrose and HPMC-sorbitol system achieved excellent performance that protected Andro-NC from crystal growth during lyophilization. During spray-drying, the impacts of types and amounts of stabilizers on the redispersibility of Andro-NCP were more significant compared to those induced by the thermal stress conditions. The polymers HPMC, PVPK30 and MCCS with high Tg played an outstanding role in preventing the Andro-NCP from breakage during spray-drying, due to the firmly steric barrier effect of polymeric stabilizers. It is concluded that Andro-NCP is subjected to agglomeration or crystal growth due to cryo/thermal stresses during drying. The polymeric stabilizers are more effective to protect Andro-NCP from the cryo/thermal damage during solidification process, which behaved strong surface adsorption and high glass transition property at different solidification stress.