Controlled Association of Amphiphilic Polymers in Water:  Thermosensitive Nanoparticles Formed by Self-Assembly of Hydrophobically Modified Pullulans and Poly(N-isopropylacrylamides)

Abstract

Thermoresponsive hydrogel nanoparticles were prepared by self-assembly of two different hydrophobically modified polymers, namely a cholesterol-bearing pullulan (CHP) and a copolymer of N-isopropylacrylamide butyl]-N-n-octadecylacrylamide] (PNIPAM-C 18Py). The interactions between CHP and PNIPAM-C18Py were investigated by fluorescence spectroscopy, dynamic light scattering, and size exclusion chromatography. After ultrasonication of a mixture of CHP and PNIPAM-C18Py (5:1 by weight) at 25°C, monodisperse nanoparticles (Dh ) 45 nm) were obtained, consisting of self-assembly of the two polymers associated via their hydrophobic moieties. Evidence from fluorescence and dynamic light scattering demonstrated that, above 32°C, the lower critical solution temperature (LCST) of PNIPAM-C18Py, the colloidal mixed nanoparticles increase in diameter (from 47 to 160 nm), but no macroscopic aggregation could be detected. This phenomenon was thermoreversible: upon cooling the particles recovered their original diameter.

Conventional Synthesis of Amphiphilic Block Copolymer Utilized for Polymeric Micelle by Mechanochemical Solid-State Polymerization

“…[29][30][31][32][33][34] When a unitary solvent, such as water, is used as a selective solvent to form star micelles, spherical micelles are obtained and other micellar shapes not formed within our knowledge. [1][2][3][4][5][6][7][8][9][10]31,32,[35][36][37][38] The PMG-Te possessed much longer hydrophilic blocks than hydrophobic blocks. Therefore, a spherical micelle would be formed by the aggregation of PMG-Te.…”

“…Such micelles have attracted much attention in drug delivery systems because of their ability to solubilize hydrophobic molecules; nanoscale size; good thermodynamic solution stability; extended release of various drugs; and prevention of rapid clearance by the reticuloendothelial system. [1][2][3][4][5][6][7][8][9][10] One needs to use model polymers with well-controlled molecular weight, narrow molecular weight distribution, and low compositional heterogeneity for systematic studies of micellar properties. Living polymerization is eminently suitable to prepare block copolymers with these properties.…”

Nanoparticles Based on Modified Polysaccharides

“…The characteristic temperature to cause a structural change of the nanoparticles decreased with an increase in the DS and the ionic strength of the medium. Moreover, they also prepared thermo-responsive nanoparticles by self-assembly of two different hydrophobically modified polymers, namely, cholesterol-pullulan and a copolymer of Nisopropylacrylamide and N-[4-(1-pyrenyl) butyl]-N-n-octadecylacrylamide via their hydrophobic moieties (Akiyoshi et al, 2000) , as well as hexadecyl group-bearing pullulan self-assembly nanoparticles (Kuroda et al, 2002).…”

Novel pH-Responsive Polymeric Micelles Prepared through Self-assembly of Amphiphilic Block Copolymer with Poly-4-vinylpyridine Block Synthesized by Mechanochemical Solid-State Polymerization

“…Considerable attention has been paid to the use of polymeric micelles in drug delivery systems because of their ability to solubilize hydrophobic molecules and their nanoscale size, good thermodynamic stability in solution, capacity for extended release of various drugs, and their resistance to rapid clearance by the reticuloendothelial system. [1][2][3][4][5][6][7][8][9] Stimulus-responsive polymeric micelles have recently emerged as a novel controlled-release system in which drugs can be released by applying an appropriate stimulus, such as a specific temperature, pH, or ultrasound. A pHsensitive polymeric micelle would be particularly useful for targeting tumor tissues, endosomes, and lysosomes because these sites are more acidic than other parts of the body, such as the blood.…”