Durable Polyelectrolyte Microcapsules with Near-Infrared-Triggered Loading and Nondestructive Release of Cargo

Microcapsules formed using a "layer-by-layer" alternating deposition of oppositely charged polyelectrolytes on sacrificial templates have reached high interest because of their facile fabrication procedure using a broad range of materials and tailored properties. However, their practical applications as microcarriers are limited as the capsules commonly suffer from low mechanical stability that can be enhanced by chemical or physical crosslinking but at the expense of decreasing permeability of the capsules' walls. It is demonstrated here that the incorporation of multiwalled carbon nanotubes in a relatively small amount (3.5%) arranged in the direction perpendicular to the capsules' walls led to an almost 20-fold increase of the apparent elastic modulus of the microcapsules as shown using the osmotic pressure method. Importantly, the introduced carbon nanotubes due to their absorption in the near-infrared region and specific arrangement enabled also a light-triggered increase of permeability of the capsules in a reversible, nondestructive manner as shown using fluorescently labeled dextrans of various molar masses. Such results imply durability and facile loading/unloading of the microcapsules that are both crucial for their practical applications as microcontainers and microreactors.