"Giant" Hollow Multilayer Capsules by Microfluidic Templating

Monodisperse microgels were synthesized by a microfluidic setup and used as a sacrificial template for the fabrication of "giant" hollow polyelectrolyte capsules with rigid walls consisting of covalently cross-linked polyelectrolytes and metal nanoparticles. First, a simple tubing-needle-based microfluidic system is utilized to produce size-monodisperse, degradable "giant" microgels consisting of dextran chains linked via carbonate esters. Second, these monodisperse microgels are subjected to a layer-by-layer coating of negatively charged platinum nanoparticles (Pt-NP'S) and a positively charged diazoresin (DAR). Three bilayers of Pt-NP'S and DAR are used to obtain a stable membrane on the microgels. Finally, the sacrificial dextran-based microgel cores are smoothly hydrolyzed and removed without rupture of the polyelectrolyte membrane due to the covalently linked hybrid polyelectrolyte/nanoparticle nature of the membrane. Scanning electron and confocal microscopy are used to characterize the capsules. The capability of encapsulating materials of interest is also shown by the addition of fluorescent polystyrene particles to the monomer mixture and subsequent visualization of embedded polystyrene particles in coated microgels after microfluidic polymerization and layer-by-layer coating. The obtained "giant" microcapsules are envisaged to be used as microreactors or drug-delivery systems.