I-GLAD: a new strategy for fabricating antibacterial surfaces.

The paper uses inverted glancing angle deposition (I-GLAD) for creating antibacterial surfaces. Antibacterial surfaces are found in nature, such as on insect wings, eyes, and plant leaves. Since the bactericidal mechanism is purely physical for these surfaces, the antimicrobial resistance of bacteria to traditional chemical antibiotics can be overcome. The technical problem is how to mimic, synthesize, and scale up the naturally occurring antibacterial surfaces for practical applications, given the fact that most of those surfaces are composed of three-dimensional hierarchical micro-nano structures. This paper proposes to use I-GLAD as a novel bottom-up nanofabrication technique to scale up bio-inspired nano-structured antibacterial surfaces. Our innovative I-GLAD nanofabrication technique includes traditional GLAD deposition processes alongside the crucial inverting process. Following fabrication, we explore the antibacterial efficacy of I-GLAD surfaces using two types of bacteria: Escherichia coli (E. coli), a gram-negative bacterium, and Staphylococcus aureus (S. aureus), a gram-positive bacterium. Scanning electron microscopy (SEM) shows the small tips and flexible D/P (feature size over period) ratio of I-GLAD nanoneedles, which is required to achieve the desired bactericidal mechanism. Antibacterial properties of the I-GLAD samples are validated by achieving flat growth curves of E. coli and S. aureus, and direct observation under SEM. The paper bridges the knowledge gaps of seeding techniques for GLAD, and the control/optimization of the I-GLAD process to tune the morphologies of the nano-protrusions. I-GLAD surfaces are effective against both gram-negative and gram-positive bacteria, and they have tremendous potentials in hospital settings and daily surfaces.