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.