Not having air conditioning in my house, here's something I didn't know: the inner surfaces of air conditioner ventilation pipes are often covered in cockroaches. Nice. In order to keep the roaches out of those pipes – along with keeping other insects out of other places – scientists from Germany's University of Freiburg have developed new bio-inspired surface coatings that even sticky-footed bugs can't cling to.

The Freiburg researchers started by observing Colorado potato beetles as they walked across a number of plant surfaces, along with replicas of those surfaces made from synthetic resins. A sensor was used to measure how much traction the beetles were able to maintain.

It was found that while surfaces consisting of curved or wavy arrangements of cells provided the most traction, the least traction was offered by surfaces that incorporated "cuticular folds." As the name suggests, these are tiny folds that occur in the protective outer cuticle of a leaf.

On surfaces with cuticular folds that are sized just right – having a height and width of about 0.5 micrometers and a spacing between 0.5 and 1.5 micrometers – the beetles have even less grip than they do on glass. This is because of the reduced contact area between the surface itself and the adhesive hairs on the insects' legs.

As an added bonus, such surfaces are also very water-repellent.

The scientists are now working on bringing man-made versions of the insect-unfriendly surfaces into commercial production, with hopes of using them not only inside of air conditioner pipes, but also on things like window frames. They also want to establish a means of adapting the sizing of the folds, in order to customize the surfaces for keeping out different types of insects.

A paper on the research was recently published in the journal Acta Biomaterialia.