For decades, when people have wanted to stick two things together but later pull them back apart, Velcro has been the answer. In the future, however, the material may get some competition from bird feather-inspired technology.

Composed of keratin (our fingernails are also made of the stuff), feathers have a central shaft going down the middle, with softer and skinnier barbs sprouting off to either side. Along the edges of those barbs are small structures known as barbules.

Those barbules hook onto one another, holding adjacent barbs together (see the microscope image below). As anyone who has ever played with a feather will know, though, the barbs can still be pulled apart, then subsequently "zipped" back together.

Tarah Sullivan, a researcher at the University of California San Diego, discovered that in birds of all sizes, the barbules are always spaced within eight to 16 micrometers of one another (a micrometer is one thousandth of a millimeter).

Keeping this ratio in mind, she proceeded to create large-scale 3D-printed models of barbs and barbules. Using these, she demonstrated that objects with such a structure could repeatedly be joined to one another and pulled apart – as is the case with the hook-and-loop structure of Velcro.

Additionally, natural barbs and barbules are capable of trapping air on a feather's underside, while diverting it on top. Sullivan believes that this quality could also be replicated in bioinspired man-made materials, which may have applications in fields such as aerospace.

"We believe that these structures could serve as inspiration for an interlocking one-directional adhesive, or a material with directionally tailored permeability," she says.

A paper on the research, which was conducted under the supervision of Prof. Marc Meyers, was published this week in the journal Science Advances.

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