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 z=+28 mV. This novel coating procedure allows the electrostatic assembly of negatively charged poly-l-lactide (PLLA, z=−19 mV) and poly-(lactide-co-glycolide) (PLGA, z=−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.