Abstract
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.
Highlights
Segregative phase separation is a common phenomenon observed upon mixing of oppositely charged polyelectrolytes.[1]
In contrast to common microreactors containing covalently immobilized enzymes on a substrate, the physical enzyme entrapment in the liquid-like core enables high-performance biocatalysis due to the fast diffusion of targeted species from and/or into the hydrogel while overcoming drawbacks related to costs, laborious purification procedures, and preservation of the native enzymatic conformation.[20−22] Driven by the potential applications of spheroidal hydrogels (SH) in biotechnology applications, we investigate the structure−property relationship of cellulosebased SH in relevant conditions and provide a proof-ofconcept application of SH as matrixes for enzyme entrapment
We found that via extruding, dropwise, a dispersion of positively charged cellulose nanofibrils, cationic cellulose nanofibril (CCNF), into an aqueous bath containing negatively charged polymer, poly(acrylic acid) (PAA), SH were formed
Summary
Segregative phase separation is a common phenomenon observed upon mixing of oppositely charged polyelectrolytes.[1]. Ionic strength and pH are crucial factors in the formation and stability of coacervates or precipitates with the coexisting phase.[2,4,5,7] For instance, Hamad et al demonstrated that by increasing the ionic strength, the coacervate exhibited a more liquid-like behavior; they attributed this to the lowering of the electrostatic attraction between oppositely charged moieties, facilitating chain motion.[5]
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