Core–Shell Spheroidal Hydrogels Produced via Charge-Driven Interfacial Complexation

Through charge-driven interfacial complexation, we produced millimeter-sized spheroidal hydrogels (SH) with a core-shell structure allowing long-term stability in aqueous media. The SH were fabricated by extruding, dropwise, a cationic cellulose nanofibril (CCNF) dispersion into an oppositely charged poly(acrylic acid) (PAA) bath. The SH have a solid-like CCNF-PAA shell, acting as a semipermeable membrane, and a liquid-like CCNF suspension in the core. Swelling behavior of the SH was dependent on the osmotic pressure of the aging media. Swelling could be suppressed by increasing the ionic strength of the media as this enhanced interfibrillar interactions and thus strengthened the outer gel membrane. We further validated a potential application of SH as reusable matrixes for glucose oxidase (GOx) entrapment, where the SH work as microreactors from which substrate and product are freely able to migrate through the SH shell while avoiding enzyme leakage.