Two-component, ultrathin microcapsules prepared by a core-mediated layer-by-layer approach

We report the preparation of two-component microcapsules by a method termed coremediated layer-by-layer (LbL) growth, which utilizes a core particle to mediate the formation of thin multilayer coatings on particles, followed by core removal. In the first (model) system to demonstrate the process, multilayers were prepared on spherical, decomposable melamine formaldehyde (MF) particles by the alternating deposition of poly(styrenesulfonate) (PSS) from solution and MF originating from partial decomposition of the MF core (in-situ acid-decomposed MF, dMF) in a pH 4.0 buffer. The core-mediated LbL method was also applied to a purely biocompatible system, consisting of a sodium alginate (Alg) coating on calcium phosphate (CaP) cores. Ultrathin, two-component PSS/dMF and Ca2+/Alg microcapsules were prepared by decomposing the multilayer-coated cores using 0.1 M hydrochloric acid. Confocal laser scanning microscopy and transmission electron microscopy verified the formation of ultrathin multilayer capsules. Binding of a positively charged fluorescent molecule (doxorubicin) to the multilayer capsules showed that the fluorescence intensity of the capsules regularly increased with increasing capsule wall thickness, confirming that the core mediates PSS/dMF and Ca2+/Alg multilayer formation. Unlike conventionally prepared polyelectrolyte capsules from sacrificial cores, which are three component systems due to the presence of decomposed core material in the oppositely charged polyelectrolyte multilayers, the microcapsules reported here are two-component, as the core material itself forms one of the multilayer components.