An insect-inspired approach to antibacterial surfaces takes off

Insects have built-in bacteria-fighting traits – traits that a team of researchers in Australia want to recreate.

Engineers at RMIT University are making antibacterial surfaces that look like the wings of a cicada or a dragonfly. Like insects, the material developed by RMIT has tiny nanopillars that rupture and kill bacterial cells.

The disinfection process requires surface modification, and no drugs or chemicals, which limits the bacteria’s ability to adapt or develop resistance. This nature-mimicking achievement could one day sustain the food and manufacturing industry as packaging, according to RMIT researcher and professor Elena Ivanova.

“We have now created a nanotexturing that mimics the bacteria-killing effect of insect wings and retains its antibacterial potency when printed on plastic,” Professor Ivanova said in a recent university press release. . .

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

Synthetic biomimetic nanostructures, however, vary widely in their antibacterial performance, and research into the optimal shape and dimensions of a nanopattern is ongoing.

Nanotexturing holds up when used in rigid plastic, but the team wants to work with softer materials.

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

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

Technical Briefs: Nanotexturing seems difficult – making fine cicada marks. Can this be achieved easily and technologically?

Professor Elena Ivanova: Over the past decade, despite an array of emerging or advanced nanofabrication techniques that allow nanotexturing of different material surfaces, it is still difficult to achieve a highly reproducible pattern with large-scale nano-dimensions.

Technical Briefs: How is nanotexturing possible now, and do you think the process will improve enough that antibacterial applications can be easily supported?

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

Often the resulting model is supposedly self-organizing and depends on the processing parameters. Therefore, designing and optimizing process parameters requires extensive knowledge, skill, and time. The nanotexturing process is certainly progressing rapidly and antibacterial applications can be easily accommodated.

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

Technical Briefs: What does this nanotextured surface look like?

Professor Ivanova: Nanotextured surfaces exhibit features such as pillars, wrinkles, or nanoscale pores. There are many examples in nature, such as on lotus leaves, shark skin and, of course, insect wings.

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

Technical Briefs: How does nanotexturing actually kill bacteria? As I try to visualize the design, it looks like the nanotexturing is just slicing and dicing the bacteria, right? Or is he hiding it somehow? Any nano-textured surface can’t really kill bacteria, can it?

Professor Ivanova: The mechanism behind the bactericidal activity associated with the nanopatterns found on cicada and dragonfly wings has been demonstrated experimentally and confirmed theoretically, in collaboration with Spanish theoretical physicists, Drs. Baulin and Pogodin. It appeared that the cell membrane is stretched when the cell is attached to the surface and breaks between the nanopillars.

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

Technical Briefs: Has this kind of cicada-inspired nanotexturing ever been done?

Professor Ivanova: Indeed, cicada-type nanotexturing has already been carried out for the manufacture of superhydrophilic surfaces with a self-cleaning effect; however, prior to the publication of our early work in 2012, it was not known that nanotextured surfaces could physically kill bacterial cells. We discovered and were the first to demonstrate that these nanostructured surfaces are antibacterial, but not repelling bacterial cells. The bacteria are physically disrupted and, more importantly, cellular debris does not accumulate between the nanopillars; they are washed in the solution.

Technical Briefs: Is this supposed to be a retroactive fix – applied to current surfaces?

Professor Ivanova: it is not so simple. Admittedly, there is a great diversity of nano-models, however, the bactericidal activity – in particular, the rate of bactericidal effectiveness – strongly depends on the interdependent topographical parameters of the nano-model; these also include the density and geometry of the nanoparticles. This means that the topographic parameters of each type of nanotextured surface must be carefully optimized in order to achieve the highest bactericidal effect.

Staphylococcus aureus bacteria are ruptured and destroyed by black silicone nanoneedles, an antibacterial surface inspired by insect wings (image magnified 30,000 times. (Photo: RMIT)

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

Professor 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 used to prevent food spoilage and contribute to the global problem of food waste. Biomimetic smart packaging has great importance in preserving food to make it marketable and to avoid food spoilage.

Technical Briefs: What’s next with the packaging?

Professor Ivanova: The results of this project are the development of highly bactericidal nanostructured polymers that are flexible, durable and suitable for a wide range of packaging solutions. Utilizing the extensive production capabilities of 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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