Chitosan/copper nanocomposites: Correlation between electrical and antibacterial properties.

Correlation between electrical and antibacterial properties of chitosan/copper nanocomposites (CS/CuNPs) is investigated. We aim at achieving the minimum CuNPs concentration in a CS-matrix while keeping high antibacterial activity. UV-vis, TEM and XRD measurements confirms the formation of polygonal metallic CuNPs (ca. 30-50 nm). Interactions between NH2/OH groups of CS and CuNPs were determined by FTIR and XPS suggesting Cu chelation-induced mechanism during the CuNPs formation. DC electrical conductivity measurements reveals a percolation threshold at CuNPs volumetric concentration of ca. 0.143%. Antibacterial assays against Gram-positive bacteria and DC measurements helps correlate the antibacterial potency to the electron transfer between the negatively charged bacteria and CuNPs. Our study suggests that nanocomposite's maximum antibacterial activity is obtained below the electrical percolation threshold at extremely low CuNPs concentrations; this fact may prove useful in the design of nontoxic nanocomposites for biomedical applications.

Combined antibacterial/tissue regeneration response in thermal burns promoted by functional chitosan/silver nanocomposites.

We report the combined antibacterial/tissue regeneration responses to thermal burns promoted by functional chitosan/silver nanocomposites (CS/nAg) with ultralow silver content (0.018wt.%, 7-30nm). Our approach allows one to produce CS/nAg nanocomposites without silver nanoparticles (nAg) agglomeration, with bactericide potency higher than 1wt.% of nAg (ca. 10nm) content and, promoting the healing process in controlled thermal burns. CS/nAg films exhibit high antibacterial activity against S. aureus and P. aeruginosa after 1.5h of incubation, demonstrating the bacterial penetration into hydrated films and their interaction with nAg. Additionally, exceptional healing of induced thermal burns was obtained by increasing myofibroblasts, collagen remodeling, and blood vessel neoformation. These factors are associated with epiderma regeneration after 7days of treatment with no nAg release. Our results corroborate the controlled synthesis of nAg embedded in CS matrix with combined antibacterial/biocompatibility properties aiming to produce functional nanocomposites with potential use in wound dressing and health care applications.