Phosphonate vs Alkoxysilane Grafting of Antibacterial Pyridyl-Pyridinium in Chitosan Films: Structure-Property...

Chitosan is a promising film-forming platform for embedding antibacterial and antiviral agents, but its moderate intrinsic bioactivity necessitates additional functionalization. Although metal nanoparticles exhibit exceptional antibacterial activity, the search for safer and more sustainable coatings dictates metal-free additives, ideally covalently anchored to prevent leaching and maintain long-term efficacy. In this work, we conceive micrometer-thick, transparent, and flexible chitosan films functionalized with pyridyl-pyridinium moieties, comparing two postgrafting chemistries (trimethoxysilane and diethylphosphonate) to elucidate their influence on film structure, stability, and bioactivity. Trimethoxysilane grafting yielded stiffer films with superior hydrolytic and thermal stability, whereas phosphonate linkers provided greater flexibility. Both routes enhanced antibacterial performance relative to pristine chitosan; silane-modified films showed stronger antimicrobial effects, while phosphonate-grafted films exhibited higher antioxidant activity. These findings highlight the distinct property-function relationships afforded by silane and phosphonate linkers, offering guidelines for the rational design of ultrastable, bioreactive chitosan coatings for antimicrobial applications.