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.

Preparación y Caracterización de Nanocompositos Quitosano-Cobre con Actividad Antibacteriana para aplicaciones en Ingeniería de Tejidos / Preparation and characterization of Copper Chitosan Nanocomposites with Antibacterial Activity for Applications in Tissue Engineering

RESUMEN: El presente trabajo describe la preparación de nanocompositos formulados a partir de quitosano (QS)/nanopartículas de cobre (nCu) con características antibacterianas y aplicación potencial en ingeniería de tejidos. Para ello, se prepararon nanocompositos mediante mezclado en solución asistido con ultrasonido con el objetivo de incrementar la dispersión de la carga nanométrica en el biopolímero. El análisis de FTIR demostró que la presencia de nCu en la matriz de QS favorece la interacción del nCu con los grupos amino/hidroxilo de la molécula del QS. Se determinó mediante UV-Vis que los nanocompositos QS/nCu presentan absorción asociada con la presencia de nanopartículas y la posible liberación de iones Cu2+ en medio líquido. Mediante AFM se determinó que el QS hidratado forma una malla con microporos, que puede favorecer la penetración de bacterias en el nanocomposito y su interacción con las nCu. Finalmente, se determinó el efecto antibacteriano del material al contacto con la bacteria Staphylococcus aureus, en donde se presenta una actividad antibacteriana superior al 90% entre los 90 y 180 min de interacción. Dichos resultados sugieren que es posible obtener nanomateriales antibacterianos biocompatibles para su posible aplicación en ingeniería tisular.

ABSTRACT: The Present work describes the preparation of nanocomposites based on chitosan (QS)/copper nanoparticles (nCu) with antibacterial properties and potential application in tissue engineering. For this purpose, nanocomposites were prepared by solution blending with ultrasound assisted, aiming to increase the nanoparticles dispersion in the biopolymer. FTIR analyses demonstrates that nCu supported in QS increase their interaction of nanoparticles with amine/hydroxyl groups of QS molecule. UV-Vis analyses demonstrates that QS/nCu nanocomposites have an absorption signal associated with the presence of nanoparticles and the possible Cu2+ ions release in liquid media. AFM analyses shown that hydrated QS form a mesh with micro pores, improving the bacterial penetration and the direct contact with nCu. This behavior was corroborated by antibacterial assays, where QS/nCu nanocomposites shown an antibacterial activity higher than 90% between 90-180 minutes of interaction. Our results suggest that is possible to obtain combined antibacterial/biocompatible nanomaterials with potential application in tissue engineering.

In vitro activity of nalidixic acid and its iron (III) complex on Entamoeba histolytica.

The in vitro activity of the antibacterial agent nalidixic acid (HNal) and its iron (III) complex (FeNal) against Entamoeba histolytica HM1 strain trophozoites in axenic or monoxenic (associated with Clostridium symbiosum) cultures was investigated. Using a dilution test with TYI-S-33 medium, this protozoan was found to be susceptible to both drugs, but FeNal showed amoebicidal activity only at concentrations higher than those used with HNal.