Bactericidal and bioinspired chitin-based anisotropic layer-by-layer brushed-nanocoating

Top-down biomimetic surfaces with micro/nanotopographic features have emerged as a strategy to prevent bacterial attachment and biofilm formation. These nanostructured surfaces mimic the nano-micro topographical features found naturally on cicada wings. However, their development requires expensive equipment and complex processes. Here, inspired by butterfly wings and crustacean exoskeletons, we present the simple design of fully bio-based, anisotropic, and antibacterial layer-by-layer (LbL) coatings based on chitin nanocrystals (ChNCs). Composed exclusively of US Food and Drug Administration-approved materials, the LbL nanocoatings were obtained by manual brushing of ChNC and Tannic Acid (TA), a natural polyphenol, coordinated by iron III (Fe3+). In contrast to those obtained by the dipping method, the brushed TA/Fe3+/ChNC coatings exhibit highly oriented ChNC nanostructures that enable contact-killing antibacterial properties against Staphylococcus aureus (a Gram-positive bacterium) and Escherichia coli (a Gram-negative bacterium). This antibacterial property is due to the orientation of the ChNC into spike-like nanotopographies with a high density of positive charge on the surface. Similar to cicada and dragonfly wings, the positively charged spikes of the oriented ChNC films are likely to damage the bacterial cell wall by (i) puncturing it upon contact with the spikes and/or (ii) stretching and tearing it when a shear force detaches the cell from the highly positive surface. The fully bio-based nature of ChNC-based nanocoatings and their brush-based fabrication method make them a suitable and affordable candidate as a sustainable antibacterial film for (bio)materials in biomedical and environmental applications.