How Geometry Affects the Adhesion of Gecko‐like Adhesives

The famous ability of geckos to climb nearly any surface originates from delicate hairs covering their toes. These so‐called setae branch into hundreds of tiny endings, the about 200 nm wide spatulae (Gekko gecko). Despite the high elastic modulus of beta‐keratine forming the setae, this hierarchical design is very compliant enabling geckos to achieve high real contact area even to rough substrates. The smart design of the setae provides not only strong attachment but also rapid and easy detachment. Mimicking these structures for technical applications requires understanding the correlation of design and functionality.

In this chapter an iterative approach for designing robust gecko‐inspired adhesives is applied for a systematic design study and adhesion analysis of gecko‐like adhesives. Applying 3D direct laser writing, a rapid prototyping technique based on multi‐photon absorption, artificial hierarchical gecko‐type structures were fabricated on the micro‐ and nanometer scale. In this way, the dimensions and elastic modulus of the inspiring example of the gecko were very closely matched. 3D direct laser writing allows arbitrary designs making this technique perfect for design studies. The influence of several design parameters like density, aspect ratio, and tip‐shape on dry adhesion performance was examined by force measurements with an atomic force microscope (AFM). Adhesion maps obtained with colloid AFM tips support the interpretation of the measured adhesion. In this way, the positive impact of mushroom‐shaped tips for stiff materials with lateral dimensions in the nanometer range is demonstrated. In addition, it is confirmed that hierarchy is favorable for artificial gecko‐inspired dry adhesives.