Ethylene Vinyl Alcohol Copolymer Nanofibrous Cation Exchange Chromatographic Membranes with a Gradient Porous Structure for Lysozyme Separation

Abstract

Lysozyme, a common antimicrobial agent, is widely used in the food, biopharmaceutical, chemical, and medicine fields. Rapid and effective isolation of lysozymes is an everlasting topic. In this work, ethylene vinyl alcohol (EVOH) copolymer nanofibrous membranes with a gradient porous structure used for lysozyme adsorption were prepared through layer-by-layer nanofiber wet-laying and a cost-efficient ultraviolet (UV)-assisted graft-modification method, where benzophenone was used as an initiator and 2-acrylamide-2-methylpropanesulfonic acid as a modifying monomer. As indicated in the Fourier Transform Infrared (FTIR) and X-ray photoelectric energy spectrometer (XPS) investigation, sulfonic acid groups were introduced on the surface of the modified nanofibrous membrane, which possessed the ability to adsorb lysozyme. Compared with membranes with homogenous porous structures, membranes with a gradient porous structure present higher static (335 mg/g) and dynamic adsorption capacities (216.3 mg/g). Meanwhile, the adsorption capacity remained high after five cycles of the adsorption–desorption process. The results can be attributed to the gradient porous structure rather than the highest porosity and specific surface area. This suggests that the membrane with comprehensive separation performance can be designed from the view of the transmembrane porous structure, which is of significance for the development of next-generation advanced chromatographic membranes.

Nanofibrous Membranes with High Mechanical Strength for the Separation and Purification of Lysozyme

“…With the increasing lysozyme concentration, the membrane’s adsorption capacity gradually decelerated, ultimately reaching saturation at a lysozyme concentration of 3 mg/mL, with a stable adsorption capacity of 336 mg/g. This result is similar to that obtained by Tang et al ( Q max = 335 mg/g) for the preparation of membrane adsorbers with a strong cation-exchange group (−SO 3 H) as a ligand, whereas we obtained similar results with a weaker carboxylate (−COOH) group providing electrostatic interaction, together with hydrophobicity given by ligands, suggesting that the MMC plays an important role. However, the hydroxyl group of RC NFM has weak hydrogen bonding interactions with lysozyme and possesses only a single force, so that its equilibrium adsorption was 30 mg/g at a lysozyme concentration of 1 mg/mL.…”