Insects have built-in, bacteria-fighting features – characteristics that a team of researchers in Australia wants to recreate.

Engineers from RMIT University are making anti-bacterial surfaces that resemble the wings of a cicada or dragonfly. Like the insects, the RMIT-developed material has tiny nanopillars that rupture and kill bacterial cells.

The disinfection process requires surface modification, and no drugs or chemicals, limiting the bacteria’s ability to adapt or develop resistance. The nature-mimicking achievement may someday support the food and manufacturing industry as packaging, according to researcher and RMIT Professor Elena Ivanova.

“We have now created a nanotexturing that mimics the bacteria-destroying effect of insect wings and retains its antibacterial power when printed on plastic,” Prof. Ivanova said in a recent news release from the university .

Ivanova and the team aim to build antimicrobial surfaces for use in medical implants and hospitals.

The synthetic biomimetic nanostructures, however, vary substantially in their anti-bacterial performance, and research on the optimal shape and dimensions of a nanopattern is ongoing.

The nanotexturing holds its own when used in rigid plastic, but the team wants to work with more flexible materials.

“Our next challenge is adapting it for use on softer plastics,” said Ivanova.

In a short Q&A with Tech Briefs below, Ivanova explains why the team’s achievement is an important step in fighting the next big superbug – and why making the surface more insect-like is far from simple.

Tech Briefs: Nanotexturing sounds difficult – making fine cicada-esque markings. Can this be achieved easily, and technologically?

Prof. Elena Ivanova: In the last decade despite an array of emerged or advanced nanofabrication techniques that allow nanotexturing of different material surfaces, it is still a challenge to achieve a highly reproducible pattern with nano-dimensions on large scale.

Tech Briefs: How is nanotexturing possible currently, and do you think the process will improve enough so that anti-bacteria applications can be easily supported?

Prof. Ivanova: This will require a long answer because there is no universal technology that applies to all materials. There are specialized nanofabrication techniques that are being developed for nanotexturing metallic surfaces, ceramics, or plastic. For example, for metals such as titanium and titanium alloys: There’s hydrothermal treatment or plasma etching. For plastics: nanoimprint lithography or oxygen plasma treatment.

Often the resulting pattern is so-called self-organized and dependent on treatment parameters. Therefore, the design and optimization of the treatment parameters require extended knowledge, skills, and time. The process of nanotexturing is certainly advancing quickly, and anti-bacteria applications can be easily supported.

The nanopillars on the surface of a dragonfly wing, magnified 20,000 times. (Photo: RMIT)

Tech Briefs: What does this nanotextured surface look like?

Prof. Ivanova: Nanotextured surfaces have features such as pillars, wrinkles, or pores at the nanoscale. There are multiple examples of these in nature, such as on lotus leaves, shark skin, and, of course, insect wings.

Indeed, 1 nanometer is 1 millionth of a millimeter; hence we have to use electron microscopy to visualize these tiny features. (see the above image)

Tech Briefs: How does nanotexturing truly eliminate bacteria? As I try to visualize the design, it seems like the nanotexturing only kind of slices and dices the bacteria, no? Or tucks it away somehow? Any nanotextured surface can’t really kill bacteria, right?

Prof. Ivanova: The mechanism behind bactericidal activity associated with the nanopatterns found on cicada and dragonfly wings was shown experimentally and confirmed theoretically, in collaboration with theoretical physicists from Spain Drs. Baulin and Pogodin. It appeared that the cell membrane is stretched when the cell is attached onto the surface and breaks in between the nanopillars.

The video shown below is a three-dimensional representation of the modeled interactions between a rod-shaped cell and the wing surface showing the physical rupturing of bacterial cell.

Tech Briefs: Has this kind of cicada-inspired nanotexturing been done before?

Prof. Ivanova: Indeed, cicada-like nanotexturing has been done previously for fabrication of superhydrophic surfaces with self-cleaning effect; however, it was not known before we published our first work in 2012 that nanotextured surfaces can physically kill bacterial cells. We discovered and were first to demonstrate that these nanostructured surfaces are antibacterial, but not through the repelling of bacterial cells. The bacteria are physically ruptured and, most importantly, the cell debris are not built up in between the nanopillars; they are washed off in the solution.

Tech Briefs: Is this meant to be a retroactive fix – applied to current surfaces?

Prof. Ivanova: It is not that simple. True, there is a great diversity of the nano-patterns, however, the bactericidal activity – specifically, the rate of bactericidal efficacy – is highly dependent on the inter-related topographical parameters of the nanopattern; these also include the density and the geometry of the nanofeatures. This means that the topographical parameters of every type of nanotextured surface need to be carefully optimized in order to achieve the highest bactericidal effect.

Golden staph bacteria being ruptured and destroyed by black silicon nanoneedles, an anti-bacterial surface inspired by insect wings (image magnified 30,000 times. (Photo: RMIT)

Tech Briefs: To be used in food packaging, will you have to wait until this can be done on flexible plastic? And is this nanotexturing on plastic a much more difficult process?

Prof. Ivanova: The application of nanotechnology in the food industry is a relatively new concept. To meet the demands of a modern society, new types of “active” packaging can be utilized to prevent food spoilage and contribute to global food waste problem. The biomimetic smart packing has a great significance in preserving the food to make it marketable and to prevent food spoilage.

Tech Briefs: What’s next with the packaging?

Prof. Ivanova: The outcomes from this project are the development of highly bactericidal nanostructured polymers that are flexible, durable, and suitable for a wide array of packaging solutions. Utilizing the extensive production capabilities of the KAITEKI Institute Inc. and Mitsubishi Chemical Holdings Corporation, the packaging will be manufactured and marketed as a viable solution to active antimicrobial packaging.

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