Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)/poly(epsilon-caprolactone) (PCL) amphiphilic block copolymeric nanospheres - II. Thermo-responsive drug release behaviors

Amphiphilic block copolymers composed of relatively hydrophilic PEO-PPO-PEO block copolymer (Pluronic) and poly(epsilon-caprolactone) with hydrophobic character were synthesized by ring-opening polymerization of epsilon-capro lactone in the presence of PEO-PPO-PEO block copolymer using stannous octoa te as a catalyst. Pluronic/PCL block copolymeric nanospheres with core-shel l structure were prepared by dialysis method. They showed the average diame ter of 116-196 nm depending on the type of copolymer. All the nanosphere sa mples exhibited a narrow size distribution. The critical micelle concentrat ions of Pluronic/PCL amphiphilic block copolymers determined by fluorescenc e spectroscopy were lower than that of the common low molecular weight surf actant. Their core-shell structure was confirmed by H-1 NMR spectroscopy. P luronic/PCL block copolymeric nanospheres exhibited the reversible change o f size depending on the temperature. Release behaviors of indomethacin from Pluronic/PCL block copolymeric nanospheres also showed temperature depende nce and a sustained release pattern. In addition, cytotoxicity test using a n MTT assay method revealed that these indomethacin-loaded Pluronic/PCL nan ospheres could remarkably reduce the cell damage compared with the unloaded free indomethacin. (C) 2000 Elsevier Science B.V. All rights reserved.