Nature-Inspired Surface Structures Design for Antimicrobial Applications

Abstract

Surface contamination by microorganisms such as viruses and bacteria may simultaneously aggravate the biofouling of surfaces and infection of wounds and promote cross-species transmission and the rapid evolution of microbes in emerging diseases. In addition, natural surface structures with unique anti-biofouling properties may be used as guide templates for the development of functional antimicrobial surfaces. Further, these structure-related antimicrobial surfaces can be categorized into microbicidal and anti-biofouling surfaces. This review introduces the recent advances in the development of microbicidal and anti-biofouling surfaces inspired by natural structures and discusses the related antimicrobial mechanisms, surface topography design, material application, manufacturing techniques, and antimicrobial efficiencies.

Keywords: anti-bacteria; anti-biofouling; anti-virus; antimicrobial surface; structure; surface topography.

Figure 1

Classification of structure-related antimicrobial surfaces and their natural inspirations. The mechano-bactericidal surface and virucidal surface kill microbes; as superhydrophobic surfaces and slippery surfaces perform self-cleaning and anti-biofouling characteristics to prevent microbial adhesion. These surfaces are inspired by cicada wings, lotuses, and nepenthes, respectively.

Figure 2

Mechanisms of bactericidal surfaces. (a) Penetration mechanisms shows that the cell wall of bacteria is penetrated by sharp structures of the bactericidal surface. (b) The stretching mechanism shows that the cell walls of bacteria may experience increased stretching tension and deformation as they land on nanostructures. The green arrows indicate the direction of cell wall movement on surface structures, and the red dots indicate the breakpoints of cell wall.

Figure 3

Antimicrobial mechanism of Cassie droplet on superhydrophobic surfaces. (a) Anti-biofouling mechanism of the Cassie droplet (compared with the Wenzel droplet) provides a smaller contact area between the liquid and the surface, allowing microbes to gather at the liquid-vapor interface between structures. At the same time, the cleaning characteristic of droplets takes the microbes off the surface. (b) Cassie droplet shows that the smaller the solid-liquid fraction, the greater the apparent contact angle is. (c) Superhydrophobic surfaces with biocide release kill microbes and bring the microbes off the surface. The green arrows indicate the direction of droplet movement and rotation on the superhydrophobic surface.

Figure 4

Approaches to obtaining superhydrophobic surfaces (a) Superhydrophobic methods, such as roughening hydrophobic surface or hydrophobic coating to a rough surface. (b) DRT structures provide upward surface tension for droplet suspension even on highly wetted materials, which have mechano-superhydrophobic and anti-biofouling characteristics.

Figure 5

Antimicrobial mechanisms of slippery surfaces. (a) The anchored lubricant layer forms a slippery surface that prevents microbes from contacting and colonizing surfaces, hence preventing microbial adhesion. (b) A slippery surface can be preloaded with biocides on the structure substrate or in the lubricant to kill microbes. The green arrows indicate the direction of droplet movement on the slippery surface.