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Shell cross-linked (SCL) thermoresponsive hybrid micelles consisting of a cross-linked thermoresponsive hybrid hydrophilic shell and a hydrophobic core domain were synthesized from poly(N-isopropylacrylamide-co-3- (trimethoxysilyl)propyl methacrylate)-b-polymethyl methacrylate (P(NIPAAm-co-MPMA)-b-PMMA) amphiphilic block copolymers. Transmission electron microscopy (TEM) images showed that the SCL micelles formed regularly globular nanoparticles. The SCL 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 degrees C, observed by turbidity measurements and dynamic light scattering (DLS). The drug loading and in vitro drug release properties of the SCL micelles bearing a silica-reinforced PNIPAAm shell were further studied, which showed that the SCL micelles exhibited a much improved entrapment efficiency (EE) as well as a slower release rate which allowed the entrapped molecules to be slowly released over a much longer period of time as compared with pure PNIPAAm-b-PMMA micelles.

A novel seven-arm star block copolymer poly(L-lactide-star block-N-isopropylacrylamide) (PLLA-sb-PNIPAAm), comprised of a hydrophobic poly(L-lactide) (PLLA) arm and an average of six hydrophilic poly(N-isopropylacrylamide) (PNIPAAm) arms, was designed and synthesized. The amphiphilic PLLA-sb-PNIPAAm copolymer was capable of self-assembling into nano-sized micelle in water, which was confirmed by FT-IR, 1H NMR and fluorescence spectroscopy. Transmission electron microscopy images showed that these nano-sized micelles were regularly spherical in shape. Micelle size determined by size analysis was around 100 nm in diameter. The micelles showed reversible dispersion/aggregation in response to temperature changes through an outer polymer shell of PNIPAAm at around 31 degrees C, observed by optical absorbance measurements. The anticancer drug methotrexate (MTX) as model drug was loaded in the polymeric nano-sized micelles. In vitro release behavior of MTX was investigated, which showed a drastic 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., ((c) 2007 Wiley Periodicals, Inc. J Biomed Mater Res, 2007.)