Key Points
Years of studying natural surfaces-like the nanopillared wings of cicadas and dragonflies-have revealed a powerful way to kill microbes: by stretching, puncturing or tearing cells the moment they land.
- Scientists are leveraging these insights to develop mechano-bactericidal surfaces made from diverse materials and patterned with nanoprotrusions, ranging from pillars to spinules.
- The surfaces could be used to prevent biofilms on medical devices, food‑processing surfaces and more.
- A thorough understanding of how mechano-bactericidal surfaces work can help improve scalability, efficacy and, ultimately, applicability.
A bacterial cell settles onto a nondescript surface. It is plump, healthy and functioning as it should. Nothing appears amiss.
But within minutes, the once taut cell is a deflated blob. Zoom in to the nanoscale, and you will see why: it was punctured to death, its corpse draped across a sea of minuscule spikes.
This demise is ultimately bad news for the bacterium. But for us, the humans impacted by surfaces contaminated with bacteria and their sticky biofilms, the effects of this "nanopatterned" surface are a welcome development.
Biofilms seed infections and can cause serious health and economic consequences, posing major headaches in health care environments and food processing facilities. The best way to mitigate biofilms is to prevent them from forming in the first place. Treating surfaces with coatings containing antiadhesive, antimicrobial or bactericidal compounds (e.g., antimicrobials and heavy metals) can help. But, depending on the surface and use, limitations like antimicrobial resistance, toxicity and depletion of the chemical agent over time can dampen their efficacy.
Which means it might be time to get physical.
Inspired by Insect Wings
Over a decade ago, Elena Ivanova, Ph.D., Distinguished Professor at Royal Melbourne Institute of Technology University, peered at a scanning electron microscopy image of a cicada wing. The wing had been dipped in a suspension of Pseudomonas aeruginosa cells and incubated overnight. Ivanova noted that bacteria were stuck to the wing-but they didn't look great.
"It was obvious that the bacteria were not healthy; the morphology was altered, and [they were] not happy," she said. "So, then we started digging, trying to understand what was happening."
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It turned out the bacteria weren't happy because they were dead.
Ivanova's path to this moment was rooted in a broader desire to understand superhydrophobic (extremely water resistant) surfaces. Her work had started with lotus leaves (a prime example of superhydrophobicity, in which water beads slide off the leaves, taking contaminants with them). The lab had since turned to other examples in nature to study how these repellent surfaces work, particularly in the context of microbial contaminants.
Enter: cicadas. Known for their multi-year breeding cycles, and occasionally deafening songs, the insects also have wings that repel water to remove dirt and debris. But when it came to shedding bacteria, Ivanova's lab found something more than water-beading was at play. "As always in science, everything comes as a surprise," she noted.
The insects' wings are covered with itty bitty protrusions, or nanopillars. Ivanova and her colleagues showed that these nanopillars killed P. aeruginosa applied to cicada wings within 3 minutes.
Additional microscopy experiments revealed the mechanism: as cells land on the nanopillars, the unsupported parts of the cell sag between pillars, stretching the membrane until it tears. "It actually cracks right in between the nanopillars," Ivanova said. Notably, when a gold coating was applied to the wings, thus altering their chemical composition, their antibacterial properties were unaffected. This result indicated that cicadas inhibit bacterial contamination of their wings through mechanical and structural means-not chemical ones.
Bactericidal nanoprotrusions have since been discovered on the wings of other insects, like dragonflies, as well as on the skin of non-insect organisms like geckos. Time and again, nature shows that a good way to combat microbial foes is to poke and prod them to death. This physical mode of bacterial destruction has inspired researchers like Ivanova to develop nanopatterned materials that could help mitigate biofilms on or in medical devices, like catheters, or in food processing facilities.
Poke, Prod and Puncture
But how does one turn insights about insects into so-called mechano-bactericidal surfaces? Different materials like metals (e.g., copper, titanium), glass and polymers can be patterned with nanoprotrusions that run the gamut of shapes, from pillars to spikes to spinules. The protrusions are created using various nanofabrication techniques; they may, for instance, be etched into surfaces with a laser or grown like crystals under highly pressurized and heated conditions.
Despite these differences, there is a sweet spot in terms of protrusion height and spacing. The nanofeatures can't be too tall or too short. They can't be too sparse, where bacteria barely encounter them. But they can't be too dense, either, as this can cause a "bed of nails" situation, where there are so many pressure points the cell sits on top, unharmed.
"You need to have a specific density and specific height and diameter of the nano features to achieve the maximum bactericidal efficiency, and that is not easy in the context of nanofabrication," Ivanova explained. Nano features are often self-organized (they spontaneously assemble into particular formations due to molecular interactions and constraints), making control over the resulting pattern tricky. One must check to see what pattern they ended up with using a scanning electron microscope before testing how well the surface kills bacteria. The structural differences between gram-negative and gram-positive bacteria also mean that, generally, there is broad variation in how effective a given surface is against microbes from each category.
How exactly nanopatterned surfaces kill is an area of active investigation. As a bacterium settles onto an array of dense, blunt nanopillars, its membrane may stretch and tear, as happens with cicada wings. Some surfaces, like those made of graphene, have layers of knife-like nanostructures that stab and slice into bacterial cells.
Rather than popping or shredding cells, mechano-bacterial surfaces can also cause them to self-destruct. Nanopillars may trigger a stress response that ends in programmed cell death; signals released by the stressed cell may cause nearby cells to destroy themselves, too. Ivanova's lab showed something similar with Candida albicans, in which a nano-pillared titanium surface triggered apoptosis of the fungus and prevented it from proliferating. Thus, mechano-bactericidal surfaces are not just useful against bacteria, but also other microbes like fungi and viruses (e.g., influenza).
Improving Scalability
But there's a hiccup: producing nanopatterned materials is difficult to do on large scales. This limits the ability to make these materials for diverse purposes. Zhejian Cao, Ph.D., a postdoctoral fellow in the Mijakovic Lab at Chalmers University of Technology, highlighted his work growing vertical nano-shards of graphene (which stab into bacteria that settle upon them) as an example.
"When we try to grow vertical graphene, we need to heat up the machine over 700°C, which means you have very limited substrate [options]," he said, noting that materials like polymer plastic would burn up under such toasty conditions. The process is also not very sustainable from an energy usage standpoint.
All is not lost, though. In a recent study, Cao and his colleagues suggested a work-around that involves coupling mechanical bacterial killing with a little Nobel Prize-winning chemistry.
The team showed that mechano-bactericidal surfaces could be based on metal-organic frameworks (MOFs)-crystalline molecular structures made of metal ions/clusters linked with organic molecules. MOFs-the subject of the 2025 Nobel Prize in Chemistry-are highly adaptable (i.e., their geometry and chemical composition can be easily modified) and, importantly, can already be synthesized at large volumes.
"You can play with them [in so many ways]. You can tune the metal ions [and] functionalize the organic molecule. Then you will have different properties of your MOF. That's why I think [MOFs] got the name 'rooms for chemistry,'" Cao said, referencing the porous structure of the molecules.
In their study, Cao's team used MOFs consisting of a zirconium-based core with iron-based spikes that, together, resemble a piece from the game of jacks. To create the mechano-bactericidal surface, the MOFs were either grown directly on a substrate or dropped on top, fully formed.
"In this way, it's actually [easier] to scale up, because then you can dropcast [the MOFs] to any kind of substrate," he shared. The surfaces can be made at lower temperatures than, say, vertical graphene, which is also a bonus. The MOF-based surfaces were bactericidal against both gram-negative and gram-positive bacteria (e.g., Escherichia coli and Staphylococcus epidermidis) by stretching, impaling or injuring the cells, with the dropcast surface showing the greatest killing efficiency (~83%) due to more comprehensive surface coverage by the nanospikes.
Other researchers are working on upscaling nanopatterned surfaces using alternative mechanisms. Ivanova and her collaborators, for instance, created nanopillar polymer films that can be used as antibacterial packaging materials, with greater ability to upscale.
"I'm confident that advances in nano fabrication will allow [us] not only to achieve accurate reproduction of specific nanoparticles on different types of the nano surfaces, [but] also in upscaling from the lab bench to the market," she said.
The Next Frontier
It's clear that mechano-bactericidal surfaces are a promising tool in the anti-biofilm toolbox. Now, it's about working out the details that, like scalability, hinder their broad application. For example, the buildup of bacterial debris on nanostructures can limit bactericidal efficacy over time. The integration of self-cleaning functionalities can help keep nanostructures primed and ready for action. Cao and his colleagues are working on mixing their MOFs with a biodegradable polymer; when bacteria land/die, they degrade the polymer to reveal a new layer of MOFs underneath. "In this way, we are trying to get long-term protection." How long the surfaces last depend on the number of MOF layers, and how thick they are.
Ivanova is less concerned with bacterial debris on nanopatterned surfaces (research from her lab suggests that bacterial cell remnants on the surfaces are so tiny, they simply float away) than she is with enhancing their overall bactericidal efficacy. "Most of the time, the surfaces…may kill bacterial cells, but they don't kill them up to 90% or 100%; they kill maybe 50% or 40%," she noted. In her mind, even 80-90% efficacy is not good enough. "We're trying to achieve complete elimination on bacterial surfaces."
Combining mechanical killing mechanisms with chemical agents or near-infrared light irradiation could enhance efficacy against diverse organisms. A thorough understanding of how mechano-bactericidal surfaces work is needed to optimize them for varying microbial targets.
Nevertheless, it's less a question of if nanopatterned surfaces will check all the boxes to be applied in "the real world," but when. Researchers have barely scratched the surface of what is possible with nanofabrication. Many of the possibilities are still unclear even to those steeped in the field-and that's the fun part.
"For most of us in science, it's the unexpected results that're the most exciting thing," Ivanova said. "Sometimes you are expecting something, and then you get something totally different-[and] maybe it's even more interesting."
Mechanisms matter. To understand how we can harness microbial life, we must first discover how it works. If your research explores the mechanistic underpinnings of microbes and their interactions, the ASM Mechanism Discovery Meeting at ASM Microbe is the place to share it.
