Long-term shelf stability of amphiphilic β-cyclodextrin nanosphere suspensions monitored by dynamic light scattering and cryo-transmission electron microscopy

Amphiphilic β-cyclodextrins (βCDa) were synthesized by statistically grafting hexanoyl carbon chains on the secondary hydroxyl functions of the βCD glucopyranosyl units. The obtained derivative was used to prepare sub-micronic colloidal nanosphere suspensions using a nano-precipitation method. The fresh suspensions contained particles with a diameter ranging from 60–100?nm. Taking into account that the physical stability of colloidal systems remains one of the major problems which can restrict their use in pharmaceutical particulate carrier formulations, the long-term stability of the aqueous nano-dispersions was investigated. Two complementary characterization methods, namely dynamic light scattering and cryo-transmission electron microscopy, were used to control the size distribution and morphology of the nanospheres during storage. The zeta potential was measured as well. An unexpected good physical stability of the suspensions after 3 year storage at room temperature was observed. This behaviour appears to be related to the small size and structural organization of the nanoparticles. The mean diameters determined from light scattering experiments are consistent with those measured from electron micrographs. The slight difference between the values obtained by both methods is discussed.