Programmable gradient-crosslinked chitosan films with dialdehyde cellulose nanocrystals and vanillic acid for...

The development of functional biopolymer films is often hampered by reinforcing fillers with a fixed crosslinking potential, which limits the ability to precisely fine-tune material properties. To overcome this, we introduce a programmable gradient-crosslinking strategy for biodegradable chitosan (CS) films. By creating dialdehyde cellulose nanocrystals (DACNC) with a controllable gradient of aldehyde contents, precise regulation over the network architecture was achieved. The incorporation of vanillic acid (VA) simultaneously conferred the film with essential bioactivities. This programmable approach allowed us to identify an optimal formulation (CDV3) that avoids the performance decline associated with over-crosslinking. Compared to the neat CS film, the CDV3 film exhibited a 63.3 % increase in tensile strength and a 31.8 % decrease in water vapor permeability. It also demonstrated potent antioxidant activity, with DPPH scavenging increasing by over 1197 %, while the film itself showed effective solid-state antibacterial activity against S. aureus and E. coli. In a practical application, the CDV3 film effectively extended the marketable shelf life of fresh blueberries to 7 days. This work establishes a clear structure-property relationship and offers a rational design principle for creating high-performance, sustainable active packaging from agricultural biomass.