Self-assembly and characterization of paclitaxel-loaded N-octyl-O-sulfate chitosan micellar system.

N-octyl-O-sulfate chitosan micellar system loaded paclitaxel was prepared by using dialysis method. The critical micelle concentration (CMC) of the modified chitosan was found to be 0.45 mg/ml. Compared with the amount of N-octyl-O-sulfate chitosan, the paclitaxel loading amount in the system was up to 25% (w/w), depending on both of the solvents used in dialysis and the feed weight ratio of paclitaxel to the derivative. The polymeric micelles forming and loading occurred simultaneously in the dialysis process when ethanol and water were utilized as the solvents for paclitaxel and the polymer, respectively. Paclitaxel-loaded micellar system of N-octyl-O-sulfate chitosan was characterized by DSC, WXRD and TEM. TEM photograph revealed that paclitaxel existed as the colloid particulates in ethanol before loading and in the cores of the spherical polymeric micelles after loading. The results of DSC and WXRD indicated that paclitaxel was transferred from the crystalline state to amorphous state after loading. The lyophilized powder of micellar system (25% (w/w) loading) could be reconstituted easily in aqueous media even after 2 months storage at 4 degrees C without the change of paclitaxel entrapment and micelle size. The reconstituted solution (2.1 mg paclitaxel/ml) also showed good stability. The dilution with saline may decrease the loading and physical stability based on the dilution times which was related with CMC of the polymer. In vitro tests showed that paclitaxel was slowly released from micellar solution and the release lasted up to 220 h by means of the dialysis method.