Preparations and temperature-and pH-dependent release property of ethylcellulose microcapsules containing N-isopropylacrylamide copolymer

摘要

Microcapsules composed of poly(N-isopropylacrylamideco-methacrylic acid) [P(NIPAM-co-MAA)] cores and ethylcellulose matrix were prepared by an emulsification and spray-drying method. First, water-inoil (W/O) emulsions were prepared using P(NIPAM-co-MAA) solution in distilled water (3%) as a water phase, and ethylcellulose solution in dichloromethane (8%) as an oil phase. The emulsion was spray-dried around 50°C to evaporate dichloromethane, and then the resulting particle was air-dried to remove residual water. Blue dextran loaded in the cores of microcapsules readily released below lower critical solution temperature (LCST) but the release was suppressed above the phase transition temperature. It is believed that the NIPAM copolymer acts as a thermal trap for blue dextran when temperature is above LCST. In addition, the microcapsules were also pH-sensitive in terms of release, which could be explained by the pH-dependent contraction and expansion of the copolymer.