Effects of pH-Sensitive Groups on Poly(ethylene oxide)-block-poly(ϵ-caprolactone) Block Copolymer Micelles Used as Drug Carriers

A new type of drug delivery system consisting of an amphiphilic polymer micelle with pH-sensitive groups is reported. The polymer comprises mPEG [poly(ethylene glycol) monomethyl ether], PCL [poly(ϵ-caprolactone)], and either PAA [poly(acrylic acid)] or PMAA [poly(methacrylic acid)]. Both mPEG -b- PCL and mPEG -b- PCL -b- PAA/PMAA are characterized by 1 H NMR, FTIR, and gel permeation chromatography (GPC). The diameters of the mPEG -b- PCL -b- PAA/PMAA micelles are found to increase with increases in pH and studies show that in vitro release of nifedipine from mPEG -b- PCL -b- PAA/PMAA micelles becomes faster as the pH value of phosphate-buffered saline (PBS) increases. This new type of pH-sensitive polymeric micelle can potentially be used as a drug carrier for oral administration of water-insoluble drugs.