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.