Top capping of nanosilver-loaded titania nanotubes with norspermidine-incorporated polymer for sustained anti-biofilm effects

Abstract

Detrimental biofilms in water and wastewater treatment systems have become a great concern. Norspermidine is a potent inhibitor for biofilm growth through a non-biocidal mechanism. Nanosilver is a widely used and efficient inorganic biocide. In this study, using a titania nanotube (TNTs) array as the loading carrier of nanosilver and a norspermidine-incorporated polymer poly(lactic-co-glycolic acid) (PLGA) as the top cap of TNTs, a composite anti-biofilm coating (TNTs-Ag-PLGA/norspermidine) with multiple effects was fabricated, and its anti-biofilm efficiency against biofilms by wastewater mixed culture was investigated. Results showed that the addition of a PLGA/norspermidine cap to the top of TNTs greatly retarded silver ion release and extended antimicrobial validity. The TNTs-Ag-PLGA/norspermidine coating showed a biofilm inhibition of 48.42 ± 2.71% after 16 days of leaching, much higher than that without the PLGA/norspermidine cap (4.10 ± 3.32%). Confocal laser scanning microscopy (CLSM) showed that the biofilm attached to the surface of the TNTs-Ag-PLGA/norspermidine showed a much lower exopolysaccharide/exoprotein ratio (0.44) compared to the control (0.94), indicating that norspermidine incorporated into the PLGA layer could act on biofilm bacteria by reducing exopolysaccharides and destroying the EPS matrix. The TNTs-Ag-PLGA/norspermidine coating inhibited biofilm formation both through a killing mechanism by silver and a non-killing mechanism of norspermidine biofilm disassembly. The combination of nanosilver-loaded TNTs and a norspermidine-incorporated PLGA cap provides a novel and effective strategy to mitigate biofilm formation by wastewater mixed cultures and has potential application in water and wastewater treatment systems.