Scientists are developing artificial surfaces that insects cannot stick to, making it harder for beetles, cockroaches and ants to walk up the sides of buildings or air conditioners in the future.
The bio-inspired, anti-adhesive surfaces are being developed by Professor Dr Thomas Speck, Dr Bettina Prum, and Dr Holger Bohn with the Plant Biomechanics Group of the University of Freiburg in Germany.
The team studied plant surfaces in order to determine what influence cell form and microstructure as well as surface chemistry exert on the adhesion behaviour of insects.
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 micrometres and a spacing of between 0.5 and 1.5 micrometres.
"That is the perfect anti-adhesion surface. The insects slip off of it much easier than off glass," said 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 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 behaviour.
They found that the beetle's adhesive power depends solely on the physical microstructure of the surface.
In the future, the anti-adhesion surfaces could be used to line the ventilation pipes of air conditioners, which are often teeming with cockroaches and other insects.
In addition, they could also be applied to facades and window frames to prevent insects that move predominantly by walking from entering the house, researchers said.
Further research will now be conducted at the Freiburg Center for Interactive Materials and Bioinspired Technologies (FIT), where the researchers will press ahead with the material development and begin constructing a prototype.
The study was published in the journal Acta Biomaterialia.
