Nanopillared surface inspired by insect wings counteracts bacteria
Keeping surfaces bacteria-free is particularly important when it comes to medical devices and implants. In a move that could replace the use of biocidal coatings and antibiotic drugs in such applications, scientists have developed a germ-repelling synthetic polymer inspired by the antibacterial powers of insect wings, which they say could form the basis of resilient new types of eye implants.
It was back in 2013 that a team of scientists took a microscope to cicada wings to reveal an array of nanoscale spikes. While each was relatively blunt on its own, the team found this grid of studs would suspend bacterium that settles on the insect's wings until it sagged into the gaps, eventually rupturing over time and dying.
Hailed as the first known instance of a living organisms eradicating microbes exclusively using its own biomaterial, this neat trick from nature inspired a new way of looking at antibacterial surfaces. And now it appears to be taking its first steps toward practical applications.
"Other research groups have also created antibacterial nanopillar surfaces, but none of their approaches can be used on ordinary polymer surfaces or be scaled up easily," says Albert F. Yee, Professor of chemical engineering and materials science at the University of California, Irvine.
Yee and his team built a flexible mold to replicate the cicada's studs with the aim of crafting an artificial cornea that doesn't require a separate coating to deal with bacteria. They then used the mold to create a curved nanopillared surface using poly(methyl methacrylate) (PMMA), a material more commonly known as Plexiglass or Lucite. The team was able to demonstrate that the matrix of tiny barbs was able to kill bacteria without harming other cells in the eye.
While promising, the team wasn't content with these initial results. Through previous research it had learnt that the nanopillars on cicada wings can kill bacteria known as "gram-negative," a group that includes E. coli and Salmonella. But when faced with "gram-positive" bacteria that feature thicker cell walls, such as Staphylococcus aureus, they are unable to eliminate the threat.
To solve this problem, the researchers are again turning to nature. Dragonfly wings also feature nanopillar patterns that fend off microbes, but these are taller and skinnier, which enables them to fend of gram-positive bacteria. The team is now working to recreate this effect on PMMA, but has encountered numerous hurdles along the way. The lean, brittle pillars tend to break when removed from the mold, which features billions of tiny cavities within an area of just a few square inches.
In an attempt to craft dragonfly-inspired antibacterial-surfaces, the team is testing out different chemical compositions to form the mold, and also incorporating fluorinated silane coatings which may help free the pillars on removal. Meanwhile, the researchers have already filed patents for the artificial cornea, with hopes of commencing animal trials this year.
"Our method is based on one developed in the early 2000s for the semiconductor industry," says Mary Nora Dickson, a graduate student in Yee's lab. "It is robust, inexpensive and can be used in industrial production. So it can now be applied to medical devices that could improve people's quality of life."
The research will be presented at a meeting of the American Chemical Society.
Source: American Chemical Society