Biomimetic Bidirectional Switchable Adhesive Inspired by the Gecko

The gecko adhesive system has attracted significant attention since the discovery that van der Waals interactions, which are always present between surfaces, are predominantly responsible for their adhesion. The unique anisotropic frictional-adhesive capabilities of the gecko adhesive system originate from complex hierarchical structures and just as importantly, the anisotropic articulation of the structures. Here, by cleverly engineering asymmetric polymeric microstructures, a reusable switchable gecko-like adhesive can be fabricated yielding steady high adhesion (F-perpendicular to approximate to 1.25 N/cm(2)) and friction ((F-perpendicular to approximate to 2.8 N/cm(2)) forces when actuated for gripping, yet release easily with minimal adhesion ((F-perpendicular to approximate to 0.34 N/cm(2)) and friction ((F-perpendicular to approximate to 0.38 N/cm(2)) forces during detachment or releasing, over multiple attachment/detachment cycles, with a relatively small normal preload of 0.16 N/cm(2) to initiate the adhesion. These adhesives can also be used to reversibly suspend weights from vertical (e. g., walls), and horizontal (e.g., ceilings) surfaces by simultaneously and judiciously activating anisotropic friction and adhesion forces. This design opens the way for new gecko-like adhesive surfaces and articulation mechanisms that do not rely on intensive nanofabrication in order to recover the anisotropic tribological property of gecko adhesive pads, albeit with lower adhesive forces compared to geckos.