Functionalization of a chemically treated Ti6Al4V-ELI alloy with nisin for antibacterial purposes

This research aims to define a protocol for nisin adsorption onto Ti6Al4V- Extra Low Interstitial content (ELI) alloy to reduce the risk of peri -implant infections. The substrate is, first, etched to get a nanotextured surface with a high density of acidic hydroxyl groups and then functionalized with the antimicrobial peptide nisin. Nisin adsorption is performed at different pH values, in the range of 5–7. The nisin release in inorganic solutions mimicking physiological or pro-inflammatory conditions is tested. The surfaces are characterized by profilometry, SEM/EDS, contact angle and surface free energy measurements, zeta potential titrations, DLS, XPS, and UV–visible spectroscopy. Effective surface adsorption was achieved and maximized at pH 6. The coated surface has high surface energy suitable for tissue integration and it releases nisin in a time longer than 1 day. As a confirmation of the antibacterial properties due to the nisin adsorption, specimens were incubated with Staphylococcus aureus, whose metabolic activity was reduced by ≈ 70% in comparison to the untreated control, and the number of viable adhered colonies was ≈ 6 times reduced. In conclusion, coupling of nisin to a chemically treated titanium surface is promising for a bioactive and antibacterial surface for tissue integration.