Almost all living organisms are uniquely adapted to the environment in which they live, some so well that researchers investigate them with the view to replicating their natural designs in products and technologies for human-use. This process, called biomimetics or biomimicry, is the exciting arena where nature and engineering meet. An example of this are cicadas and dragonflies whose wings are coated with tiny pointed ‘nanopillars’ that impale and kill bacterial cells which land on them. Now, researchers from University of California, Irvine have replicated these antibacterial nanopillars on synthetic polymers that are being developed to restore vision. The study was presented at the 251st National Meeting & Exposition of the American Chemical Society.
Previous studies from other groups have have also developed antibacterial nanopillar surfaces, as it stands, none of these developments could be used on ordinary polymer surfaces or be scaled-up easily. Earlier studies from the lab showed that their cicada wing nanopillars can kill gram-negative bacteria, a group of microorganisms which include E. coli. However, the cicada nanopillars were unable to kill gram-positive bacteria as these microbes have thicker cell walls. Wiping out these bacteria, which include MRSA and Streptococcus, is important because they cause infections on medical devices and in hospitals. Therefore, the team decided to investigate dragonfly wing nanopillars which are taller and skinnier, and can kill gram-positive bacteria. The current study follows the proof-of-concept to form these types of nanopillars on PMMA.
The current study utilises a method which is based on one developed in the early 2000s for the semiconductor industry. The group note that it is robust, inexpensive and can be used in industrial production, therefore it can now be applied to medical devices that could improve people’s quality of life.
One such proof-of-concept from the lab is an artificial cornea that they aim to construct from PMMA. The team explain that the material is already commonly used in medical devices including implantable intraocular lenses and traditional hard contact lenses. They go on to add that by building nanopillars into the surfaces of these types of devices, they plan to make them bactericidal without the need for a separate biocidal coating or antibiotic drugs.
The researchers state that one version of the process uses commercial molds that contain billions of tiny pits in an area that covers just a few square inches. Results show that pressing the mold onto a heated polymer film reshapes the film, leaving it decorated with nanopillars once the mold is removed. Data findings show that this method works just fine for the stubbier cicada-like pillars, however, the finer dragonfly-like pillars tend to break apart when the mold is removed. Therefore, the lab is experimenting with fluorinated silane coatings for the mold which could help free the pillars when it’s time to remove the polymer film; they are also testing different chemical compositions for the mold itself.
The team surmise that they are now applying their technique to an artificial cornea and the cicada nanopillared PMMA surface produced retains the ability to kill bacteria without harming other kinds of cells in the eye. For the future, the researchers state that they are developing a mold for the taller, dragonfly-type pillars. They go on to conclude that they have filed for patents on the bactericidal surface and artificial cornea application and hope to begin animal trials this year.
Source: American Chemical Society (ACS)
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