Gecko-Inspired Dry Adhesive for Robotic Applications

Geckos have the supreme ability to rapidly attach and detach from almost any kind of surface. This ability is attributed to the hierarchical structure of their feet and its articulation to generate strong adhesion and friction forces on gripping cycle and comes off the surface within milli seconds during the releasing cycle. This phenomena has inspired the fabrication of structured surfaces for robotic applications. In this study, micron-sized rectangular flaps composed of polydimethylsiloxane (PDMS) were fabricated using massively parallel micro-electromechanical systems (MEMS) techniques with the intention of creating directionally responsive, high-to-low frictional-adhesion toe pads exhibiting properties similar to those found in geckos. Using the Surface Forces Apparatus (SFA), we investigated the friction and adhesion forces of both vertical (symmetric) and angled/tilted (x-y-z asymmetric) micro-flaps under various loading, unloading and shearing conditions. We find that the anisotropic structure of tilted micro-flaps gives very different adhesion and tribological forces when articulated along different x-y-z directions: high friction and adhesion forces when articulated in the y-z plane along the tilt (+y) direction, which is also the direction of motion, and weak friction and adhesion forces when articulated against the tilt (-y) direction. Our results demonstrate that asymmetric angled structures, as occur in geckos, are required to enable the gecko to optimize the requirements of high friction and adhesion on gripping, and low frictional-adhesion on releasing. These properties, when coupled with suitable articulation mechanisms, produce a reversible adhesive system.