Ideas

Brainiac

A gecko walks into a museum...and cleans up

Hadi Izadi

The red balls are “dust particles” and the green rods are the gecko-inspired fibrils. A key thing to convey in the caption is that the shape of the tips of the fibrils attracts the dust, then conveys it up the length of the fibril, which clears the tip to pick up more dust.

The same remarkable climbing ability that enables the gecko to scale walls has inspired an innovative new approach to cleaning works of art.

The technique involves a thin film covered on one side with microscopic fibrils, pole-like structures similar to the ones that allow geckoes to create uniquely thorough contact with whatever surface they’re walking over. This contact generates low-level forces of attraction that could be useful for museum conservators who are always trying to find better ways of removing dust from art.

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“Any two materials, if you bring them into contact, they have physical attraction,” says Hadi Izadi, a postdoctoral engineer at Yale. “If you increase the contact area and increase the interfacial interaction, these surfaces act like an adhesive.”

Standard adhesives, like Scotch tape, create a pressure sensitive bond — they contain a liquid-like material on one side that when pressed, embeds into the roughness of the material they’re now attached to. The resulting bond is strong, but it would also create a lot of collateral damage if it were used to extract dust from the Mona Lisa. Given that, museums have a number of gentler methods, everything from lambs wool dusters to HEPA vacuums to infrared lasers.

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“Dust is . . . never just dust,” says Pam Hatchfield head of objects conservation at the Museum of Fine Arts. “It might be acidic, it might be alkaline it, might have strong abrasives in it so if you wiped it over the surface of something that had a fine surface, you could damage it.”

This is where the gecko comes in: Its unparalleled climbing ability has long mesmerized scientists, who’ve tried to recreate it in everything from a better bandage to devices that allow humans to climb walls. Geckoes are able to adhere so closely to surfaces—and detach so quickly—thanks to the fibril structures on the pads of their feet. These fibrils are made from keratin, the same hard material found in your fingernails, but they’re soft and flexible because they’re of such slender proportions. The fibrils allow geckos to adapt the bottoms of their feet to the contours of the surface—far more closely, for example, than your fingertips mold to whatever object you’re holding.

The net effect of such thorough coverage is a strong bonding force. Whenever two materials come in contact, there are forces in play that work to hold them together. One is an electrostatic charge — this is the charge that adheres dust so persistently onto non-conducting surfaces like acrylic paintings (or your dining room table) in the first place. The other is Van der Waals’ forces, which describe the attractive force between molecules. The more completely in contact two surfaces are, the stronger these forces become, and the flexible nature of a gecko’s fibrils allows it to increase that contact area many times over.

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Izadi, working in the lab of T. Kyle Vanderlick, dean of the School of Engineering at Yale, engineered a gecko-like fibril structure into a thin film that resembles a piece of tape even though it works completely differently. The larger the fibrils the more effective they are at picking up larger particles of dust. (In general, fibrils can adhere dust particles with diamaters as large as one-eighth to one-third their own diameters.) The fibrils Izadi has created range in width from 2 to 50 micrometers (five one-thousandths of a centimer) and they’re twice as tall as they are wide. They have a flat tip with rounded edges, which promotes just enough adhesion to collect dust, but not so much that the fibrils damage the artwork. The design also causes dust particles to advance up the fibrils each time the material is adhered to a surface, which clears the fibril tips to attract additional dust particles. Even small adjustment in the structure of the fibrils would dramatically alter their adhesive properties.

Izadi and his collaborators have filed for a patent on the technology and are in conversation with companies that might apply this dust removal technique in other sensitive areas, like high-tech manufacturing. The Yale team is also currently working with conservators at the university’s Institute for the Preservation of Cultural Heritage to refine the gecko adhesive for actual museum use.

Kevin Hartnett is a writer in South Carolina. He can be reached at kshartnett18@gmail.com.
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