The creation of antibacterial fibres through physical adsorption of polyelectrolytes

Abstract: Contact-active antibacterial surfaces with irreversibly attached antibacterial com-pounds are a sustainable alternative to traditional biocides. No chemicals are released into nature and the antibacterial mechanism reduces the risk of the evolution of re-sistant bacteria. However, the preparation of such surfaces is far from sustainable, as organic solvents and harsh reaction conditions commonly are required. An alter-native option is to use polyelectrolyte multilayers (PEM), based on physical ad-sorption, which can be performed in water-based solutions at room temperature. Although contact-active antibacterial PEMs have been reported previously, this is the first study of renewable cellulosic wood fibres.The build-up of cationic polymer polyvinylamine (PVAm) and anionic polyacrylic acid (PAA) multilayers on model surfaces was studied to optimise adsorption. The amount of adsorbed polyelectrolytes was continuously growing with increasing number of layers, but remained dense and flat as the number of layers increased. The largest adsorption was obtained at a high salt concentration, which shielded the repulsion between the polymers.Model surfaces were also used to evaluate the influence of the polymer and number of layers on the antibacterial properties. Multilayers on model surfaces showed a low bacteriostatic effect, with up to approximately 40 % inhibition for 3 layers of un-modified PVAm/PAA. In contrast, when the same multilayers were applied on cel-lulosic fibres, bacterial-growth inhibition of > 99.9% was obtained. Hydrophobically modified PVAm did not yield better results, despite being superior in solution. An increase in fibre charge by fibre oxidation led to the largest amount of adsorbed pol-ymer and the best antibacterial properties, an effect that lasted for weeks. Electron microscopy study of bacteria on the fibres showed that the bacteria interacted more on a highly charged surface and that the morphology of the bacterial cell could be affected. The effect was suggested to be due to electrostatic interaction with the pos-itively charged modified fibres. The promising results offer the possibilities of a new generation of antibacterial surfaces based on a renewable resource.