Few things are as disconcerting, or as curious, as the sight of a gecko or spider skittering effortlessly upside down along the ceiling. This ability is known to be facilitated by microscopic hairs or "setae" on the footpads of insects and mammals and a better understanding of their function could lead to advances in synthetic adhesives, wall climbing robots and yes, even the the holy-grail of the spiderman suit. Now for the first time, scientists studying leaf beetles have been able to measure the adhesive force from single setae in a live animal and in the process expand our knowledge of the role they play in clinging to diverse surfaces.
The individual setae on a beetle's feet are minute at only 1/200th of a millimeter across. To assess their properties, researchers James Bullock and Walter Federle from the University of Cambridge in England used a fine glass cantilever and observed its deflection through a microscope at the point of hair detachment, which allowed them to measure the "stickiness" of each individual hair as well as analyze the specific function of different types of setae.
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It is known that the leaf beetle has three shapes of adhesive hair arranged in a distinct pattern across its feet. Some are pointed, some are flat or "spatula-tipped", and some are disk-shaped and their arrangement suggested specific biological functions for each hair type.
It was found that the disk-shaped hairs were not only stiffer, but more adhesive than other hairs, perhaps providing greater stability to the insect and on smooth surfaces. They may also confer a greater ability to hang on to the back of females during copulation. The spatula-tipped hairs were the next "stickiest", followed finally by the pointed hairs. The researchers hypothesized that these less sticky hairs may enable running upside down by facilitating rapid detachment.
"The question of how forces in natural adhesive systems run from the single-hair to the whole-animal level is a central, unresolved problem. Its understanding will be a prerequisite for the design of bio-inspired synthetic adhesives," said Bullock and Federle.
The study was published online in the Journal Naturwissenschaften – The Nature of Science.