Self-assembled, thermosensitive micelles of a star block copolymer based on PMMA and PNIPAAm for controlled drug delivery

A four-arm star block copolymer, comprised of a hydrophobic PMMA arm and an average of three hydrophilic poly(N-isopropylacrylamide) (PNIPAAm) arms were designed and synthesized from the molecular level. The amphiphilic star block copolymer is capable of self-assembling into micelles in water, which was confirmed by FT-IR, 1H NMR and fluorescence spectroscopy. Transmission electron microscopy images showed that these nanoparticles were regularly spherical in shape. 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 34 °C, observed by optical absorbance measurements. Resulted polymeric micelles loaded with prednisone acetate showed a much improved drug release behavior due to the special micellar structure.