Interfacial complexation induced controllable fabrication of stable polyelectrolyte microcapsules using all-aqueous droplet microfluidics for enzyme release.

Water-in-water ( w/ w) emulsions are particular advantageous for biomedical related applications, such as cell encapsulation, bioreactors, biocompatible storage and processing of biomacromolecules. However, due to ultralow interfacial tension, generation and stabilization of uniform w/w droplets is a challenge. In this work, we report a strategy of creating stable and size controllable w/w droplets that can quickly form polyelectrolyte microcapsules (PEMC) in a microfluidic device. A three-phase (inner, middle, outer) water system were applied to create streamline of inner phase which could be broken into droplet via a mechanical perturbation frequency, with size determined by the streamline diameter and vibration frequency. The interfacial complexation is formed via electrostatic interaction of poly-cations of poly(diallyldimethylammoniumchloride) (PDDA) with poly-anions of polystyrene sodium sulfate (PSS) in the inner and outer phases. With addition of negatively charged SiO nanoparticles, the stability, permeability and mechanical strength of the PEMC shell could be well manipulated. Prepared PEMCs were verified by encapsulating FITC labeled dextran (FITC-Dex) molecules and stimuli triggered releasing by varying pH value or osmotic pressure. A model enzyme, trypsin, was successfully encapsulated into PEMCs, and released without impairing their catalytic activity. These results highlight its potential applications for efficient encapsulation, storage, delivery and release of chemical, biological, pharmaceutical and therapeutic agents.