One-Step Schiff Base Assembly of MOF-Chitosan IPN Hydrogels for α-Glucosidase Immobilization and Inhibitor Fishing

Abstract

Enzyme immobilization in hydrogels improves stability and reusability, while conventional single-network hydrogels often suffer from insufficient mechanical robustness and poor protection against environmental stressors. Herein, we report a one-step, room-temperature strategy for constructing metal–organic framework (MOF)-cross-linked interpenetrating polymer network (IPN) hydrogels via dynamic Schiff base chemistry between dialdehyde-terminated poly(ethylene glycol), ε-polylysine, and chitosan (CS) in the presence of ZIF-8 nanoparticles. α-Glucosidase (α-Glu) is simultaneously entrapped in situ to give the immobilized enzyme α-Glu@PPC/ZIF-8. Through systematic compositional optimization coupled with CS-free control hydrogels (PP and PP/ZIF-8), the distinct contributions of CS and ZIF-8 to the network scaffold are quantitatively deconvoluted. CS serves as the essential structural backbone: its addition alone increases the storage modulus (G′) from ∼3.4 × 10–4 kPa (PP, CS-free) to ∼43.3 kPa (A6, 6% CS), a more than five-order-of-magnitude enhancement, whereas ZIF-8 nanoparticles act as secondary reinforcing nodes. The optimal formulation (6% CS, 3 mg ZIF-8) achieves an exceptional balance among stiffness, toughness, and mass transport capacity. The immobilized α-Glu@PPC/ZIF-8 exhibits broad pH tolerance, retains 93.6% activity after 28 days of hydrated storage at −20 °C, and maintains 98.4% activity after seven consecutive catalytic cycles. Most distinctively, it retains ≥95% activity after 10 min of exposure to ten out of 12 common organic solvents covering a wide polarity range, substantially outperforming the CS-free counterparts. Coupled with HPLC, this platform enables selective affinity-based ligand fishing of two bioactive α-glucosidase inhibitors─2,4-dimethoxy-6,7-dihydroxyphenanthrene and batatasin I─from Dioscorea opposita Thunb. peel extracts, with blank-gel controls confirming binding specificity. This work provides a quantitative structure–property–function framework for designing high-performance MOF-IPN hydrogel composites and offers a robust platform for enzyme immobilization.