Cicada wings and shark denticles may hold the solution to creating antibacterial hospital surfaces.
Keeping surfaces free of bacteria is one of the most complex issues faced at hospitals. For doctors and patients, it is essential to reduce contact with bacteria, but bacteria thrive on the metal and plastic surfaces common in hospitals. Biomimicry might provide an innovative solution to this problem. Scientists have begun to explore how some animals naturally repel or kill harmful bacteria. These scientists are looking in unlikely places, from insects in leafy trees to fish in the deep sea.
Most people know cicadas for the noise they make in the spring and summer when they gather in leafy, deciduous trees. Scientists from Spain and Australia, however, have been studying them for something else. They have examined the structure of cicadas’ wings and have found that those wings have antibacterial properties. Now in the wake of COVID-19, and inevitable future pandemics, we can begin to imagine how this strategy could be emulated in our medical facilities. But first we need to understand how the wing’s structure functions.
The surface structure of cicada wings is composed of spiky, cone-shaped nanopillars. The nanopillars are around 200 nanometers tall. These tiny nanopillars provide the main antibacterial property of the wings. Their structure kills bacteria cells. As bacteria cells land on a cicada wing, the cells make contact with the nanopillars and begin to slide downwards. As they slide, the cone shape of the nanopillars stretches their membranes. Eventually, the nanopillars tear the membrane of the cell, killing the bacterium. Less rigid bacteria cells are stretched and killed easily, while bacteria cells with a rigid structure and membrane are able to defy the nanopillars for a longer amount of time.
Scientists from Kansai University in Japan conducted an experiment to test the antibacterial properties of the cicada wing structure. To do so, they replicated the cicada wing’s nanopillar surface using a silicone board as the base of the wing and resin beads as the nanopillars. Then, the scientists placed E. Coli molecules on this surface. They found that “after 24 hours the [E. Coli’s] survival rate was far below 1 percent.” This is a huge reduction compared to a plain silicon board for which, “the bacteria survival rate… was in the range of several tens of percent.” The positive result of this experiment gives hope to mimicking the structure of cicada wings and greatly reducing bacterial survival on hospital surfaces.
Diving from the trees into the deep sea, scientists have found another promising antibacterial surface for hospital use. Shark skin is covered in v-shaped scales called denticles. These denticles act similarly to the nanopillars on cicada wings. When bacteria or other microorganisms land on the surface of a shark’s skin, the denticles create mechanical stress on the cell’s membranes. This stress damages the cells’ shape and ability to move, eventually killing the bacteria.
Inspired by this naturally antibacterial surface, a company called Sharklet™ Technologies has created a material modeled after the structure of shark skin. The Sharklet material mimics the pattern of shark denticles — v-shaped scales that line a shark’s skin — to produce the same antibacterial effects as shark denticles. Sheets of the Sharklet™ material can be used to coat plastic hospital surfaces and medical devices, altering the current surface to have the qualities of shark skin.
Scientists from Sharklet™ have tested this material by comparing it to a common smooth surface and a copper alloy surface, which has antimicrobial and antibacterial properties. They sprayed these surfaces with a solution that included the bacteria MRSA and MSSA. These surfaces were then tested for MRSA and MSSA 90 minutes later. After 90 minutes, MSSA on the Sharklet surface was reduced by 97 percent compared to the smooth control surface and the copper alloy surface. The MRSA on the Sharklet surface was reduced by 94 percent compared to the smooth surface, while copper reduced MRSA by 80 percent compared to the smooth surface. The substantial reduction of bacteria on the Sharklet™ surface presents an exciting possibility in the future of healthier hospital surfaces.
Innovative solutions to healthcare problems can be found in many places. However, as the importance of clean, antibacterial hospital surfaces grows, so does the importance of looking for solutions in unique places. From the sea to the sky, the answers to many of our complex issues can be found in the nature that surrounds us.
Faye Berry is a rising senior at Lower Merion High School in Pennsylvania. She has enjoyed nature from a young age and continues to explore the world around her.
