Enzymatic Bio-Oxidation of Ethyl Hydroxyethyl Cellulose and UV-Assisted Cross-Linking with Chitosan for Enhanced Aqueous Stability in Biomaterial Production

Ethyl hydroxyethyl cellulose (EHEC) is a promising sustainable biomaterial, but its high hydrophilicity limits its use in moisture-resistant applications. Conventional cross-linking to improve aqueous resistance often requires toxic reagents, organic solvents, or high temperatures. Here, we developed a green cross-linking method by enzymatically oxidizing EHEC with laccase/TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl), followed by UV-induced cross-linking with chitosan at room temperature, yielding a robust macromolecular network. The optimal conditions (4 h oxidation, 50 wt % chitosan, 24 h cross-linking) yielded prolonged aqueous-stable films that maintained structural stability for 3–5 months in aqueous media, depending on pH. Compared to purified EHEC, the biomaterial exhibited enhanced thermal behavior, a 44% increase in elastic modulus (775.6 ± 172.8 MPa), reduced hydrophilicity (75.2 ± 0.7° contact angle, compared to 56.5 ± 0.6° from the original EHEC film), and no release of toxic compounds in cytotoxic assays with L929 fibroblast cells. This methodology is tunable and efficiently produces stable, sustainable EHEC-based films, demonstrating significant promise for advanced aqueous applications and active-ingredient encapsulation.