Thermo-responsive microcapsules using poly(N-isopropylacrylamide)

Two different types of thermo-responsive microcapsules were prepared by combining biodegradable polymer microcapsules and poly(N-isopropylacrylamide) (PNIPAAm). First, PNIPAAm was grafted on the surface of the polypeptide microcapsule by a new method of surface grafting. Dextran release from the microcapsule was faster below the lower critical solution temperature (LCST) of PNIPAAm than the rate above it. Then the temperature changed across the LCST, a reversible and thermo-responsive release from the microcapsule was observed. Notably, the transition of the release rate by changing the temperature occurred quickly in a narrow temperature range. Secondly, poly(L-lactic acid) (PLLA) microcapsules containing PNIPAAm gel were prepared. Internal cavities of PLLA microcapsules were filled partly or completely with PNIPAAm gel to obtain microcapsules for thermo-responsive drug release. The dextran release from the microcapsules showed a positively thermo-responsive release as the release was accelerated at the temperatures above the LOST, and nearly stopped below the LCST. The release rate of dextran was dependent on the amount of PNIPAAm gel loaded in the microcapsules as well as on the size of the internal cavities. The response rate of the microcapsules was also fast.