pH-Triggered Dynamic Stabilization of PEG/Dextran-Based Water-in-Water Emulsions Using Double-Hydrophilic PEG- b -PAAc Copolymers for Sustainable Biocatalytic Microreactors

Water-in-water (W/W) emulsions represent a promising strategy for compartmentalizing, protecting, and controlling the release of sensitive bioactive ingredients (e.g., vitamins, probiotics, flavors) within entirely aqueous environments. However, their on-demand stabilization and destabilization for recyclable biocatalysis remains challenging. Here, a pH-responsive water-in-water (W/W) emulsion was developed using the amphiphilic block copolymer PEG 45 - b -PAAc 113 as a smart stabilizer and applied for enzymatic catalysis. Compared with traditional emulsion systems, this pH-responsive W/W emulsion system not only exhibits excellent biocompatibility but also enables in situ product separation, thereby enhancing enzymatic catalytic efficiency. Reversible emulsification and demulsification mechanism is governed by pH-triggered conformational switching of PAAc blocks, and this reversible emulsification behavior can be achieved through pH cycling (pH 5 → 10 → 5). When applied to the horseradish peroxidase (HRP)-catalyzed conversion to tetraguaiacol, HRP was enriched in the Dex phase, while the hydrophobic product preferentially migrated to the continuous PEG phase. This in situ separation alleviates integration challenges between reaction and separation steps in biocatalytic processes. As a result, the system achieved a 15.3% increase in product yield and a 21.7% enhancement in catalytic efficiency ( k cat /K m = 59.133 μM –1 s –1 ) compared to a pure Dex solution, and exceeded the performance of unstabilized emulsions by 49.4% in catalytic efficiency and 13.1% in yield. By combining reversible stability with intelligent product separation, this all-aqueous Dex/PEG emulsion constitutes a recyclable and efficient microreactor, offering a strategy for the development and application of responsive polymers.