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.