Microwedge Machining for the Manufacture of Directional Dry Adhesives

Directional dry adhesives are inspired by animals such as geckos and are a particularly useful technology for climbing applications. Previously, they have generally been manufactured using photolithographic processes. This paper presents a micromachining process that involves making cuts in a soft material using a sharp, lubricated tool to create closely spaced negative cavities of a desired shape. The machined material becomes a mold into which an elastomer is cast to create the directional adhesive. The trajectory of the tool can be varied to avoid plastic flow of the mold material that may adversely affect adjacent cavities. The relationship between tool trajectory and resulting cavity shape is established through modeling and process characterization experiments. This micromachining process is much less expensive than previous photolithographic processes used to create similar features and allows greater flexibility with respect to the microscale feature geometry, mold size, and mold material. The micromachining process produces controllable, directional adhesives, where the normal adhesion increases with shear loading in a preferred direction. This is verified by multi-axis force testing on a flat glass substrate. Upon application of a post-treatment to decrease the roughness of the engaging surfaces of the features after casting, the adhesives significantly outperform comparable directional adhesives made from a photolithographic mold.