Fabrication of uniform "smart" magnetic microcapsules and their controlled release of sodium salicylate.

Uniform stimuli-responsive ("smart") magnetic chitosan or chitosan/poly(N-isopropylacrylamide) microcapsules were successfully prepared by using carboxyl-functionalized polystyrene particles as a core template. Magnetic nanoparticles (FeO) were dispersed on the surface of microcapsules under mild conditions and the "smart" response of microcapsule shells was still retained. The structure and morphology of magnetic microcapsules were characterized by SEM, TEM, XRD and TGA. Microcapsules were prepared after removing the polystyrene core by exposing it to solvent, and the microcapsules exhibited a hollow structure. The magnetic nanoparticles also appeared on the surface of microcapsules and the chitosan/poly(N-isopropylacrylamide) composite microcapsules could be readily and quickly collected by an external magnetic field. The pH values of the aqueous dispersion and the temperature response properties of the magnetic microcapsules were investigated with sodium salicylate as the hydrophilic drug.