pH-temperature-sensitive supramolecular micelles based on cyclodextrin polyrotaxane

BACKGROUND: Based on the assembly strategy induced by host-guest recognition in weak selective solvent, a kind of supramolecular nano-micelles has been self-organized from a water-soluble diblock copolymer, poly(ethylene oxide) -block-poly(acrylic acid) (PEO-b-PAA), selectively included by -cyclodextrins (-CDs). RESULTS: The spontaneous aggregation of rod-like -CD/PEO-based pseudo-polyrotaxanes (pseudo-PRs) drove the formation of square-piece in aqueous media and thereafter evolved to spherical assemblies with or without hollow structure as time prolonged, which were stabilized by uncovered hydrophilic PAA segments. Such morphological evolvement attributed to hydrogen bonding between center dot center dot CCOOH in PAA and center dot center dot COH in -CD. However, when alkaline media was used to inhibit hydrogen bonding by ionizing.-CCOOH, the assemblies were only uniform spheres of ca. 100 mn. Meanwhile, the order stacking of PR rods became the basic building units all the time. Herein, the supramolecular PRs contributed to temperature-response character, namely the formation of assemblies is reversible stimulated with temperature changes. Additionally, the inhibition of deceasing pH to the ionization of free PAA segments made assemblies fuse as microspheres. CONCLUSION: Such pH- and temperature-sensitivity as well as the biocompatibility of components and water as media make a great potential of such nano-particles as the biomedical materials with controlled-release function. (c) 2007 Society of Chemical Industry