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Materials

Gecko-inspired adhesion controlled by light

Adhesive grips and releases objects thanks to UV-triggered azobenzene chemistry

by Ryan Cross
January 19, 2017 | APPEARED IN VOLUME 95, ISSUE 4

Credit: Sci. Robotics
Under UV light, azobenzene (R = various groups) changes conformation from trans to cis, allowing the adhesive to lift up.

A team of German researchers have created an adhesive pad inspired by the sticky feet of geckos that unsticks from objects when triggered by ultraviolet light. The pad could lead to robotic fingers controlled by light that can pick up and release delicate objects.

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Credit: Shutterstock
Credit: Shutterstock
[+]Enlarge
Credit: Shutterstock
Credit: Shutterstock

Geckos can scurry up and down walls thanks to about half a million fibers called seta on each of their feet. Each setae is divided into hundreds of spatula-like nanostructures that individually grip a surface through weak van der Waals interactions. Collectively, these millions of interactions lead to strong adhesion.

In the new work, Emre Kizilkan of Kiel University and his colleagues used previously developed surfaces with mushroom-shaped polydimethylsiloxane microstructures to produce geckolike adhesion. But for easy manipulation, they desired a system that could attach and detach its adhesive hold at will. “We wanted to control the adhesion by light,” Kizilkan says.

To do so, the team incorporated a stretchy liquid crystalline elastomer layer containing azobenzene molecules underneath the adhesive pad. Azobenzene undergoes a trans to cis isomerization in the presence of UV light, which causes the adhesive layers to bend (Sci. Robotics 2017, DOI: 10.1126/scirobotics.aak9454). The layers revert to normal when the researchers turn off the UV light.

When the adhesive surface lies flat against an object, it sticks. Under UV illumination, the adhesive bends, releasing the bulk of its contact with the object, relinquishing its grip. Kizilkan showed that the device could move objects such as glass beads and glass slides.

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