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A Gecko‐Inspired Reversible Adhesive

Geckos, as well as many insects, have evolved a robust reversible adhesion mechanism, enabling them to traverse rough, smooth, vertical or inverted surfaces. This feat is enabled by a hierarchical structure of 20mm diameter setae splitting into 200 nm wide spatulae. The setae are able to conform to the microscale roughness of a surface, enabling the spatulae to make intimate surface contact – enhancing shortrange van der Waals interactions. In addition, the hierarchical structure provides a fast and effective release mechanism. Here we report, for the first time, the fabrication and demonstration of a synthetic, fully reversible adhesive. The biomimetic system is composed of 10mm wide, 130mm long flexible nickel paddles which are suspended parallel to and above the substrate, and which are coated by 200 nm diameter aligned vertical polymeric nanorods (analogous to the gecko’s setae and spatulae, respectively). When subjected to a magnetic field, the nickel paddles undergo a reversible conformational change, greatly reducing the contact area, and decreasing adhesion by a factor of 40. The mechanism of adhesion in the gecko has been of scientific interest since Aristotle. Since then scientific investigations have revealed much about the construction of the pad in the gecko’s foot. Most recently there has been an intensifying scientific investigation into the fundamental physics of the adhesive, isolating van der Waals as the primary source of adhesion, with additional evidence that humidity may also play an important role. Van der Waals interactions produce weak and short-range forces, therefore the gecko must create a large amount of intimate surface contact to have enough adhesion to hang from a vertical or inverted surface. The gecko accomplishes this with a highly compliant pad structure, which allows it to conform to surfaces, without creating a large amount of elastic repulsive force. This ability to comply to a wide range of surfaces, from the curvature of a tree branch to microand nano-scale roughness