Micellar formation of poly(caprolactone-block-ethylene oxide-block-caprolactone) and its enzymatic biodegradation in aqueous dispersion

The water-insoluble triblock copolymer poly(epsilon-caprolactone-b-ethylene oxide-b-epsilon-caprolactone) (PCL-b-PEO-b-PCL) can form core-shell-like polymeric micelles in aqueous solution where the core and shell are respectively made of collapsed hydrophobic PCL and swollen hydrophilic PEO blocks. Four PCL-b-PEO-b-PCL triblock copolymers with different PEO/PCL molar ratios were prepared and characterized. The degradation of these copolymer micelles in the presence of enzyme lipase PS was much faster than the bulk PCL or PCL thin film. The degradation kinetics was investigated using a combination of laser light scattering and pH measurements. The results revealed that the in-situ biodegradation of the copolymer chains inside the micelle could be effectively monitored by a pH meter, while laser light scattering measures the biodegradation-induced dissociation of the micelles in water. The effects of the enzyme and copolymer concentrations as well as the PCL/PEO molar ratios on the biodegradation kinetics were studied.