Gecko-Inspired Adhesives with Asymmetrically Tilting-Oriented Micropillars.

The anisotropic adhesion behavior of the gecko is closely related to their feet and is comprised of keratinous hairs, setae, where van der Waals forces permit attachment and detachment during locomotion. Previous research either achieved only isotropic adhesion behaviors or involved the complicated photolithography method. Here, we reported a simple way to achieve the anisotropic adhesion behaviors of gecko-inspired adhesives, consisting of micropillars with asymmetrically tilted orientation via the 3D printing technique. The adhesive forces of structured polymer pillars achieved 4-fold stronger, compared to controls with the plain surface. The anisotropic adhesion behavior is presented on the patterned surface and is two times stronger along the gripping direction compared to the releasing direction on the adhesives, which is attributed to the asymmetric stress distributions at the edges, as well as the stresses resulting from the moment with the sheared top. The finite element analysis is applied to demonstrate the stress distributions and displacement variations. This work provides the insight into the design and fabrication of gecko-inspired adhesives with anisotropic adhesion behaviors in practical applications.