Facile fabrication of well-defined hydrogel beads with magnetic nanocomposite shells

Well-defined magnetic nanocomposite beads with alginate gel cores and shells of iron oxide (γ-Fe2O3) nanoparticles were prepared by self-assembly of colloidal particles at liquid–liquid interfaces and subsequent in situ gelation. Fe2O3 nanoparticles could spontaneously adsorb onto the water droplet surfaces to stabilize water-in-hexane emulsions. Water droplets containing sodium alginate were in situ gelled by calcium cations, which were released from calcium-ethylenediamine tetraacetic acid (Ca-EDTA) chelate by decreasing pH value through slow hydrolysis of d-glucono-δ-lactone (GDL). The resulting hybrid beads with a core–shell structure were easily collected by removing hexane. This facile and high efficient fabrication had a 100% yield and could be carried out at room temperature. Insulin microcrystal was encapsulated into the hybrid beads by dispersing them in the aqueous solution of alginate sodium in the fabrication process. The sustained release could be obtained due to the dual barriers of the hydrogel core and the close-packed inorganic shell. The release curves were nicely fitted by the Weibull equation and the release followed Fickian diffusion. The hybrid beads may find applications as delivery vehicles for biomolecules, drugs, cosmetics, food supplements and living cells.