Charge-Tunable μ-Gelzymes Achieving Cellulose Affinity under Synergistic Ionic Liquid-Pretreated Biomass in Situ Saccharification

Enzyme-loaded microgels (μ-Gelzymes) have gained increasing attention for their facile fabrication, versatile applicability, and fine controllability. Herein, a series of poly(N-isopropylacrylamide) (PNIPAM)-based μ-Gelzymes (P-C) with a tunable surface potential were prepared to improve the cellulase biocatalytic effect. The P-C showed better cellulose affinity than free cellulase, highly reducing its nonproductive binding onto lignin, while the Langmuir adsorption affinity indexes (K) of P-C for cellulose and lignin were 1.19 and 0.34 g/L, whereas those of free cellulase were 0.44 and 3.92 g/L, respectively. Moreover, the biomass synergistic pretreatment with 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc) and choline acetate ([Ch]OAc) resulted in an almost equal ζ-potential on lignin, cellulose, and hemicellulose. Microcrystalline cellulose (MCC) and bagasse (BC) substrate conversions achieved by P-C were 19.8 and 12.1% higher than those with free cellulase under 3% [Ch]OAc + 7% [EMIM]OAc in situ saccharification. The P-C ζ-potential and biomass glucose production demonstrated that the more the electroneutrality on P-C, the higher the glucose generation, suggesting that biomass saccharification can be controlled by adjusting the surface charge on μ-Gelzymes.