Microporous regenerated cellulose-based macrogels for covalent immobilization of enzymes

In this study, regenerated cellulose-based macrogels with abundant carboxyl groups and interconnected microporous structures were synthesized from cellulose fibers (CFs)/cellulose nanofibers (CNFs) and utilized as stable, efficient, and recyclable platforms for enzyme immobilization. CNFs with different carboxyl contents were prepared by a TEMPO (2, 2, 6, 6 -tetramethylpiperidine-1-oxyl radical)-medium oxidation system. The cellulose-based macrogels were prepared by dissolving CFs and CNFs in a NaOH/urea aqueous solution and a followed extrusion process. The carboxyl groups within the macrogels were then activated by an N-(3-Dimethylaminopropyl)-N’-ethylcarbodiimide hydrochloride (EDC·HCl)/Nhydroxysuccinimide (NHS) system, which provides these macrogels with efficient binding sites for enzyme immobilization. The three-dimensional network structures of the macrogels facilitate the enzymes to infiltrate into the core of the macrogels and be fixed on the abundant pore walls. The immobilized enzymes maintain activity at a higher pH than free enzymes. Moreover, the immobilized enzymes have higher temperature tolerance, and their optimal reaction temperature is about 10 °C higher than that of free enzymes. The immobilized enzymes retain 24% of the initial activity after repeated use for 7 times. The microporous regenerated cellulose-based macrogels show potential in the fields of enzyme immobilization and biocatalysis.