Lowly Gecko Source of Inspiration for New Adhesion Process Controlled by Light
Inspiration for new chemical process applications sometimes come from a close study of nature itself. Such is the case with chemists in Germany who recently developed a new adhesion process by examining the feet of a small, commonly found lizard.
A team of German researchers has developed a new adhesion pad as a result of studying the Gecko, the small lizard often seen scurrying up and down walls. The secret to the Gecko’s amazing maneuverability is its sticky feet which give them traction on just about any surface in any direction quickly.
The scientists’ close examination of the Gecko’s feet found something amazing. They are full of millions of fibers called seta. Each seta is divided into hundreds of spatula-like nanostructures that individually grip a surface through weak interactions. But collectively, these millions of interactions lead to strong adhesion.
The German team, from Kiel University, used previously developed surfaces with mushroom-shaped polydimethylsiloxane microstructures to produce gecko-like adhesion. The challenge was to find a way to control the adhesion. They needed a system that would attach or detach its hold at will. They came up with the idea of controlling the adhesion by light.
To accomplish this, 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 cause the adhesive layer to bend. The layers revert back to normal when the researchers turn off the UV light.
When the adhesive surface lies flat against an object, it sticks. However, UV illumination acts to make the adhesive bend, releasing the grip on the object. This releases the bulk of its contact with the object and relinquishes its grip. The team demonstrated that the device could move objects such as glass beads and glass slides.
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