Formulation of Next‐Generation Multicompartment Microcapsules by Reversible Electrostatic Attraction

The combination of several active substances into one carrier is often limited due to solubility, stability and phase‐separation issues. These issues have been addressed by an innovative capsule design, in which nanocapsules are assembled on the microcapsule surface by electrostatic forces to form a pH‐responsive hierarchical capsule@capsule system. Here, melamine‐formaldehyde (MF) microcapsules with a negative surface charge were synthesized and coated with a novel MF‐polyethyleneimine (PEI) copolymer to achieve a positive charge of ζ=+28 mV. This novel coating procedure allows the electrostatic assembly of negatively charged poly‐l‐lactide (PLLA, ζ=−19 mV) and poly‐(lactide‐co‐glycolide) (PLGA, ζ=−56 mV) nanocapsules on the microcapsule surface. Assembly studies at pH 7 gave a partial surface coverage of PLLA nanocapsules and full surface coverage for PLGA nanocapsules. The pH‐responsive adsorption and desorption of nanocapsules was shown at pH 7 and pH 3.