Opposite world: developing anti-adhesion surfaces

The power of the metaphor/analogy is demonstrated in a Sept. 24, 2013 news item on ScienceDaily where they’ve mentioned insects in the context of anti-adhesion—the opposite of how insects are usually referenced, i.e., how well they stick to surfaces and the search for better adhesives. Or you could put it down to lazy reading on my part as it took me a minute or so to make sense of what I was reading (from the news item),

Beetles, cockroaches, and ants will have a harder time walking up the sides of buildings or air conditioners in the future — thanks to the bio-inspired, anti-adhesive surfaces Prof. Dr. Thomas Speck, Dr. Bettina Prüm, and Dr. Holger Bohn are developing together with the Plant Biomechanics Group of the University of Freiburg. The team studied plant surfaces in order to determine what influence cell form and microstructure as well as surface chemistry exert on the adhesion behavior of insects.

The Sept. 24, 2013 University of Freiburg (Germany) press release,which originated the news item, describes the research and the new anti-adhesive surface in more detail,

The researchers conducted adhesion experiments in which Colorado potato beetles walked across differently structured plant surfaces as well as replicas made of synthetic resins. The team used a highly sensitive sensor to measure the traction forces of the beetles on various surfaces. They discovered that wavy or strongly curved cells can increase the adhesive powers of beetles, whereas microstructures composed of wax crystals or cuticular folds reduce them. The latter are tiny folds in the cuticle, a protective layer on the surface of the leaf resembling polyester. The beetles had the hardest time walking on surfaces with cuticular folds with a height and width of approximately 0.5 micrometers and a spacing of between 0.5 and 1.5 micrometers. “That is the perfect anti-adhesion surface. The insects slip off of it much easier than off glass,” says project director Thomas Speck. The cuticular folds reduce the contact area between the adhesive hairs on the beetles’ legs and the plant surface. Unlike on more coarsely structured surfaces, the beetle can’t dig its feet firmly into the cuticular folds. Thus, the microstructure of the surface has a stronger effect on the adhesion of the beetle than the cell form.

The team also took contact angle measurements to investigate the wettability of the various surfaces. The researchers used hydrophobic and hydrophilic artificial moldings of the microstructured plant surfaces in order to study the influence of the surface chemistry on surface wettability and the beetles’ walking behavior. Much like wax crystals, cuticular folds are very good at repelling water. In contrast to the wettability, which depends on both the microstructure and the surface chemistry, the walking behavior of the beetles is not influenced by the surface chemistry. This means that the beetle’s adhesive power depends solely on the physical microstructure of the surface.

Here’s a link to and a citation for the researchers’ paper,

Plant surfaces with cuticular folds and their replicas: Influence of microstructuring and surface chemistry on the attachment of a leaf beetle by Bettina Prüm, Holger Florian Bohn, Robin Seidel, Stephan Rubach, and Thomas Speck. Acta Biomaterialia Volume 9, Issue 5, May 2013, Pages 6360–6368

This paper is behind a paywall.

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