Indometacin-loaded micelles based on star-shaped PLLA-TPGS copolymers: effect of arm numbers on drug delivery

Star-shaped copolymers based on star-shaped poly (L-lactide) (s-PLLA) and tocopheryl polyethylene glycol 1000 succinate (TPGS) (s-PLLA-TPGS) were synthesized with structural variation on arm numbers in order to investigate the relationship between the arm numbers of s-PLLA-TPGS copolymers and their micelle properties. The structure and Mw of s-PLLA-TPGS were characterized with 1H NMR, GPC, DSC, and XRD. The indometacin(IMC)-loaded s-PLLA-TPGS micelles were obtained by dialysis method. The effects of arm numbers of s-PLLA-TPGS copolymers on surface morphology, particle size, zeta potential, drug loading content (LC), drug encapsulation efficiency (EE), and in vitro drug release behavior of prepared micelles were studied. The results indicated that the average diameters, LC, and EE of IMC-loaded s-PLLA-TPGS micelles gradually increased in the order of 4-arm, 5-arm, and 6-arm s-PLLA-TPGS copolymers. The in vitro release studies showed that the IMC accumulative release can be decreased by increasing the arm numbers of the s-PLLA-TPGS copolymers, and the release profiles of IMC from the s-PLLA-TPGS copolymers followed the Baker-Lonsdale model equation. The results suggest that the arm number regulation of s-PLLA-TPGS copolymers can provide a new strategy for designing drug carriers of high efficiency.