Thermoresponsive release from poly(L-lactic acid) microcapsules containing poly(N-isopropylacrylamide) gel

Abstract

Many internal cavities of poly(L-lactic acid) (PLLA) microcapsules have been filled partly or completely with poly(N-isopropylacrylamide) (PNIPAAm) gel by two different procedures to obtain microcapsules for thermoresponsive drug release. In one procedure, the PLLA microcapsules have been incubated with N-isopropylacrylamide (NIPAAm) for different hours, and the polymerization has been carried out by using a redox initiator. The longer the incubation time, the more PNIPAAm gel is loaded. In the other procedure, the internal cavities of PLLA microcapsules fully loaded with PNIPAAm gel have been prepared by evaporation of a w/o/w emulsion after the polymerization of NIPAAm contained in the internal aqueous phase. Dextran as a model drug has been loaded in the microcapsules, and the release has been examined at two different temperatures which are above or below the lower critical solution temperature (LCST) of PNIPAAm. The dextran release is accelerated above LCST, and nearly stops below LCST. The release rate of dextran is dependent on the amount of PNIPAAm gel loaded in the microcapsules as well as on the size of the internal cavities which is controllable by the preparation method of w/o emulsion.