Multiresponsive Microcapsules Based on Multilayer Assembly of Star Polyelectrolytes

Abstract

Star polyelectrolytes (poly­(<i>N</i>,<i>N</i>-dimethylaminoethyl methacrylate) (PDMAEMA)) with dual (temperature and pH) responsive properties were utilized to fabricate multiresponsive microcapsules via layer-by-layer (LbL) assembly. The LbL microcapsules are very robust and uniform, with higher stability and different internal structure compared with conventional microcapsules based on linear polyelectrolytes. Ionic strength in the polyelectrolyte solution during the microcapsule assembly process has a significant influence on the thickness and permeability of microcapsules. With increasing pH, the permeability of microcapsules decreases, and the transition from “open” to “closed” state for target molecules can be achieved within a narrow pH range (from pH 7 to 8). On the other hand, the overall size and permeability of the microcapsules decrease with increasing temperature (with a shrinkage of 54% in diameter at 60 °C compared with room temperature), thus allowing to reversibly load and unload the microcapsules with high efficiency. The organization and interaction of star polyelectrolytes within confined multilayer structure are the main driving forces for the responsiveness to external stimuli. The multiresponsive LbL microcapsules represent a novel category of smart microstructures as compared to traditional LbL microcapsules with “one-dimensional” response to a single stimulus, and they also have the potential to mimic the complex responsive microstructures found in nature and find applications in drug delivery, smart coatings, microreactors, and biosensors