UC Riverside

Bacterial contamination and biofilm formation on material surfaces remain major challenges in USDA-relevant food and agricultural environments, where durable coatings are needed to reduce microbial attachment, persistence, and cross-contamination, including from multidrug-resistant pathogens. Silk fibroin is an attractive coating platform because it is a biocompatible structural protein whose surface chemistry and interfacial behavior can be tailored through chemical modification. In this study, silk fibroin was functionalized with 1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) using EDC/NHS coupling to create a phosphonate-modified surface with enhanced ion-binding capability and altered wettability. The resulting silk-HEDP materials were characterized by Fourier transform infrared (FTIR) spectroscopy, water contact angle measurements, and calcium depletion experiments. FTIR confirmed successful incorporation of phosphonate functionality while preserving the characteristic amide features of silk. Secondary-structure analysis further indicated changes in the relative β-sheet and α-helix contents after modification and post-treatment, showing that chemical grafting influenced both surface composition and protein organization. Contact-angle measurements showed that silk-HEDP exhibited a lower water contact angle than unmodified silk, consistent with increased surface hydrophilicity due to the introduction of polar phosphonate groups. Calcium depletion assays demonstrated substantially greater ion-binding interactions for silk-HEDP than for unmodified silk and glass controls. Overall, covalent HEDP grafting provides an effective route to engineer silk-based coatings with tunable structure, wettability, and calcium-chelating functionality, establishing a promising platform for future antimicrobial and antifouling surfaces aimed at limiting bacterial attachment and biofilm development.