One‐Step Synthesis of Hydrogen‐Bonded Microcapsules for pH‐Triggered Protein Release

One‐step microfluidic approach in which interfacial complexation of hydrogen bonding polymers is utilized to prepare pH‐responsive microcapsules is presented. Using water‐in‐oil‐in‐oil‐in‐water (W₁/O₁/O₂/W₂) triple‐emulsion droplets as templates, it is shown that polymeric microcapsules with an aqueous core and a shell that consists of two complementary hydrogen bonding polymers, poly(propylene oxide)(PPO) and poly(methacrylic acid)(PMAA), can be prepared in a robust manner. The presence of a buffer layer enables controlled interfacial complexation of PMAA and PPO at the water/oil interface, followed by spontaneous dewetting of the oil droplet to result in hydrogen‐bonded microcapsules dispersed in aqueous media. In addition, it is demonstrated that the permeability of the PPO/PMAA membrane can be readily tuned by varying the molecular weight of PMAA. Furthermore, it is shown that the resulting PPO/PMAA microcapsules are stable at a high salt concentration (>1 m NaCl) unlike analogous capsules prepared through electrostatic complexation while they release the encapsulated protein above the critical pH of which the PMAA ionizes and results in disassembly of the shell membrane.