Fabrication of Nano-engineered Stainless Steel to Prevent Biofilm Formation by Foodborne Pathogens

Introduction: Biofilms, the surface-associated complex communities of bacteria, adhered to both biotic and abiotic surfaces, have been explored in omnipresent environments. In particular, surface structure and related nano/microscale fabrication technologies have been intensively studied for prevention of microbial adhesion and consequent biofilm formation.

Purpose: This study demonstrated nanofabrication and anti-biofilm characterization of the self-cleanable surface on stainless steel substrates.

Methods:   The 304 grade stainless steel surfaces were electrochemically etched in dilute Aqua Regia solution, consisting of 3.6% HCl and 1.2% HNO₃, at various voltages (5, 10, 15, and 20 V) and treatment times (5, 10, 15, and 20 min) to fabricate hierarchical nanoporous structures. Under static and dynamic flow environments, Escherichia coli, Salmonella Typhimurium, Listeria monocytogenes, and Pseudomonas aeruginosa PAO1 were used for testing antibacterial adhesion and antibiofilm performances of the developed surfaces.

Results: Differences in applied voltage and treatment durations led to variations in the etch rate and surface morphologic characteristics. The plates treated at 10 and 15 V showed nanoscale pores, which are needed to improve the self-cleanability, while maintaining the intrinsic food grade quality of stainless steel. The etched samples coated with an additional hydrophobic Teflon layer showed a maximum static water contact angle above 150°. The surfaces etched at 15 V with Teflon coating, compared to the control stainless steel, showed significant antibacterial adhesion effects (P < 0.05) in both static and dynamic flow conditions.

Significance: The successful fabrication of superhydrophobic etched surfaces can be used in food industries to prevent biofilm development, resulting in the improvement of food safety.