Layer-by-layer assembled microcapsules: Fabrication, stimuli-responsivity, loading and release

Layer-by-layer (LBL) assembly of polymers and polymers/small molecules on colloidal particles forms core-shell particles, which produce hollow microcapsules with a layered structure after core removal. This article reviews the recent progress in driving forces for fabricating the LBL microcapsules, intelligent stimuli-responsivity and loading and release properties. The manipulation of the electrostatic and hydrogen bonded microcapsules by chemical crosslinking in terms of their structures and properties is first presented. Then the microcapsules based on new driving forces, i.e. covalent interaction, base pair and host-guest interaction, are introduced. The microcapsules thus obtained are responsive to pH, temperature, charge, light, electricity, magnetic field and chemical compounds. The typical loading and release properties and techniques established so far, such as direct encapsulation by the multilayers, pre-adsorption or pre-incorporation into the templates and charge controlled deposition, are discussed subsequently. Finally, aiming at the target delivery of the microcapsules and functional capsule devices, the methods for arraying the microcapsules on the substrates based on the electrostatic interaction and bioconjugation are described.