Self-assembled thermoresponsive micelles of poly( N-isopropylacrylamide- b-methyl methacrylate)

Abstract

To achieve a combination of spatial specificity in a passive manner with a stimuli–response targeting mechanism, a temperature-responsive polymeric micelle was prepared using block copolymers of poly( N-isopropylacrylamide- b-methyl methacrylate) (PNIPAAm- b-PMMA). The critical micelle concentration of amphiphilic block copolymers in aqueous solution was determined by fluorescence spectroscopy using pyrene as a fluorescence probe. Transmission electron microscopy images showed that these nanoparticles were regularly spherical in shape. Micelle size determined by size analysis was around 190 nm. The micelles showed reversible dispersion/aggregation in response to temperature cycles through an outer polymer shell lower critical solution temperature (LCST) for PNIPAAm at around 33 °C, observed by optical absorbance measurements and dynamic light scattering (DLS). The anti-inflammation drug prednisone acetate was loaded as the model drug in the polymeric nanoparticles. In vitro release behavior of prednisone acetate was investigated, which showed a dramatic thermoresponsive fast/slow switching behavior according to the temperature-responsive structural changes of a micellar shell structure. The reversible and sensitive thermoresponse of this micelle might provide opportunities to construct a novel drug delivery system in conjunction with localized hyperthermia.