An Integrated Bio‐Based Film With Dynamic Covalent Networks for Coupled pH‐Responsive Release and Colorimetric Reporting

ABSTRACT

A multifunctional smart film was fabricated via dynamic Schiff base cross‐linking between quaternary ammonium chitosan (HACC) and dialdehyde cellulose (DAC), enabling the integrated encapsulation, controlled release, and visual indication of curcumin within a single matrix without external sensors. Structural analyses (FTIR, XPS) confirmed the formation of the pH‐responsive dynamic network. Curcumin incorporation significantly enhanced the film's performance, increasing tensile strength (TS) by ∼60%, improving barrier properties, and providing potent antioxidant activity (DPPH scavenging efficiency approaching 90%). The swelling behavior and release kinetics of the films were highly pH‐dependent. Rapid burst release dominated by nonFickian diffusion was observed under acidic conditions (pH 4.0), whereas slow, sustained Fickian diffusion‐controlled release occurred in neutral and alkaline environments (pH 7.0 and 9.0). Owing to the intrinsic chromophoric properties of curcumin, the films displayed distinct and reversible pH‐dependent color changes, transitioning from bright yellow in acidic media to reddish‐brown in alkaline conditions, enabling intuitive visual monitoring of environmental changes. This work demonstrates an effective strategy for designing bio‐based innovative packaging materials that integrate sensing, protection, and controlled release functions within a unified, dynamically responsive polysaccharide network.