Nanostructural antimicrobial coatings containing chitosan produced by self-assembly technique (layer-by-layer) for textile substrates

The research on bioactive materials, especially coatings, enables the production of resistant, nontoxic, biodegradable, and suitable antimicrobial surfaces for contact with food or humans. This project combined the effect of different types of chitosan in the manufacture of nanostructured films for antimicrobial coatings on textile substrates and silicon slides. Chitosan-based thin films were assembled using the layer-by-layer technique and the axial composition was accessed by X-ray photoelectron spectroscopy with depth profiling. Chitosan (Chi) samples possessing different average degree of acetylation (DA) and viscosity average molecular weight (Mv) were used in this study as well as two different polyanions, namely sulfonated polystyrene (SPS) and carboxymethyl cellulose (CMC). When chitosan, a positively charged polymer in aqueous acidic medium was combined with a strong polyanion (SPS), the total positive charge of chitosan, directly related to its average degree of deacetylation, was the key factor affecting the film formation and its structure. However, when a weak polyanion (CMC) was combined with chitosan, pH and viscosity average molecular weight of chitosan strongly affected film structure and composition. Following, we studied the molecular interdiffusion in thin films of CMC/Chi. There are few studies in the literature which explore the diffusion of a negatively charged polymer (in our case, the SPS) into a biopolymer thin film. This system illustrated in a simple way how chitosan interacts with different macromolecules (CMC and SPS). Higher binding energy values were observed for the Chi/SPS complex, as a result of the strong electrostatic interactions between the polymers. The CMC/Chi system is complemented with electrostatic interactions of weaker nature (i.e. hydrogen bounds). These changes in the binding energies were verified by the XPS high resolution spectra and provided a better understanding of LbL systems containing chitosan. Finally, we explored the spray LbL approach as a methodology to easy scale-up and capable of reducing the time required for the film build-up in comparison to the traditional dipping method. The variation of chitosan architecture, polyanion pair and pH shows that it is possible to molecularly control the chemical and structural properties of nanostructured coatings at the molecular level, thus opening up new possibilities to adapt them for the desired application, as shown by the antimicrobials tests. (author)