Preparation of core-shell type nanoparticles of poly(epsilon-caprolactone)/poly(ethylene glycol)/poly(epsilon-caprolactone) triblock copolymers

A triblock copolymer based on poly(epsilon -caprolactone) (PCL) as the hydr ophobic part and poly(ethylene glycol) (PEG) as the hydrophilic portion was synthesized by a ring-opening mechanism of epsilon -caprolactone with PEG containing a hydroxyl group at both ends as an initiator. The synthesized b lock copolymers of PCL/PEG/PCL (CEC) were confirmed and characterized using various analysis equipment such as H-1 NMR. DSC, FT-IR, and WAXD. Core-she ll type nanoparticles of CEC triblock copolymers were prepared using a dial ysis technique to estimate their potential as a colloidal drug carrier usin g a hydrophobic drug. From the results of particle size analysis and transm ission electron microscopy, the particle size of CEC core-shell type nanopa rticles was determined to be about 20-60 nm with a spherical shape. Since C EC block copolymer nanoparticles have a core-shell type micellar structure and small particle size similar to polymeric micelles, CEC block copolymer can self-associate at certain concentrations and the critical association c oncentration (CAC) was able to be deter mined by fluorescence probe techniq ues. The CAC values of the CEC block copolymers were dependent on the PCL b lock length. In addition, drug loading contents were dependent on the PCL b lock length: the larger the PCL block length. the higher the drug loading c ontent. Drug release from CEC core-shell type nanoparticles showed an initi al burst release for the first 12 hrs followed by pseudo-zero order release kinetics for 2 or 3 days. CEC-2 block copolymer core-shell type nanopartic les were degraded very slowly, suggesting that the drug release kinetics we re governed by a diffusion mechanism rather than a degradation mechanism ir relevant to the CEC block copolymer composition.