Antibacterial and non-cytotoxic ultra-thin polyethylenimine film.

In recent years, a common strategy, to obtain more uniform and controlled synthesis of polyelectrolytes multilayers (PEMs), relies on a previous polyethylenimine (PEI) coating of the substrate surface. PEI is a synthetic cationic polymer which provides a positive charge distribution on the materials to be covered with PEMs. Despite being an important step, this pre-layer deposition is frequently overlooked and no comprehensive characterizations or deep discussions are reported in literature. In that sense, this work reports on the synthesis of a typical PEI film that works as a precursor for PEMs, and its detailed physicochemical characterization. As many PEMs are produced for antibacterial and biomedical applications, the cytotoxicity of the film was also tested using fibroblasts, and its antibacterial activity was studied using Staphylococcus aureus and Pseudomonas aeruginosa. Our results present the formation of an ultra-thin film of PEI with a thickness around 3.5nm, and with a significant percent of NH3+ (35% of the total amount of N) in its chemical structure; NH3+ is a key chemical group because it is considered an important bacterial killer agent. The film was stable and did not present important cytotoxic effect for fibroblasts up to 7days, contrary to other reports. Finally, the PEI film showed high antibacterial activity against the S. aureus strain: reductions in cell density were higher than 95% up to 24h.

Hyaluronan/chitosan nanofilms assembled layer-by-layer and their antibacterial effect: A study using Staphylococcus aureus and Pseudomonas aeruginosa.

In the last few years, chitosan-based coatings have been proposed as antibacterial surfaces for biomedical devices in order to prevent nosocomial infections. In that sense, this work reports the optimized synthesis of hyaluronan/chitosan (HA/CHI) nanofilms assembled layer-by-layer in order to maximize the antibacterial effect for two important human pathogenic bacteria, Staphylococcus aureus and Pseudomonas aeruginosa. In this assembly, HA forms a soft, highly hydrated, and nontoxic film, whereas CHI shows the antimicrobial characteristics. Our HA/CHI nanofilm synthesis optimization was based on changing pH values of the biopolymer stem-solutions and the consequent variation of their ionization degree. Furthermore, the surface density of primary amino groups, which are related to the antibacterial effect, was also enhanced by increasing the number of HA/CHI bilayers. The antibacterial effect of HA/CHI nanofilms was evaluated by the spread plate counting method for both bacteria. These results were correlated with the morphology of nanofilms (characterized using SEM and AFM), as well as with their chemical properties studied by UV-vis, Kelvin Probe Force microscopy and XPS spectroscopy.