Stimuli-Responsive Hollow Polymer Nanoparticles for Use as Novel Delivery Systems

The preparation of biocompatible N-isopropylacrylamide-co-acrylic acid polymer on sacrificial silica (SiO2) nanoparticles is reliably carried out using conventional free radical polymerization. Subsequent removal of the SiO2 core with diluted hydrofluoric acid leads to the formation of uniform hollow polymer structures containing COOH functional groups. The formation and properties of polymer-coated SiO2 and hollow polymer nanoparticles are thoroughly examined by electron microscopes, X-ray photoelectron spectroscopy, and dynamic light scattering. The resulting hollow nanoparticles (approximately 200 nm in diameter) exhibit much greater diameter changes (i.e., swelling and deswelling) than those of polymer-coated SiO2 nanoparticles as a function of pH and/or temperature. This is presumably due to the presence of a large hollow cavity in the polymer nanoparticles. Given their unique features, including their high guest molecule loading capacity, surface functional groups, homogeneity, external stimuli-responsiveness, and biocompatible nature, these hollow nanoparticles can serve as the novel biomedical delivery systems.