Nanoengineering of polymeric capsules with a shell-in-shell structure

Polymeric capsules possessing a shell-in-shell structure were fabricated by assembling layers of polyelectrolytes with interlayers of silica nanoparticles onto microspheres of melamine formaldehyde. Subsequently the cores were removed with hydrochloric acid and the silica layers with hydrofluoric acid. Removal of the silica layers leaves an aqueous phase of a poly(allylamine hydrochloride) solution between an outer and an inner polyelectrolyte shell. The interlayer thickness could be varied by the diameter of silica particles or by the number of deposition steps. The double-shell structure of the microcapsules was determined by scanning force microscopy, confocal laser scanning microscopy, and transmission electron microscopy on ultramicrotome sections in detail. In contrast to one-shell capsules of polyelectrolytes, the permeability for small molecules does not change with time and temperature. In addition, the shell-in-shell capsules exhibit a remarkably higher mechanical stability as shown by experiments of osmotically induced deformations.