Gecko‐Inspired Dry Adhesive for Robotic Applications

Abstract

Most geckos can rapidly attach and detach from almost any kind of surface. This ability is attributed to the hierarchical structure of their feet (involving toe pads, setal arrays, and spatulae), and how they are moved (articulated) to generate strong adhesion and friction forces on gripping that rapidly relax on releasing. Inspired by the gecko's bioadhesive system, various structured surfaces have been fabricated suitable for robotic applications. In this study, x–y–z asymmetric, micrometer‐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 a surface forces apparatus (SFA), the friction and adhesion forces of both vertical (symmetric) and angled/tilted (x–y–z asymmetric) microflaps under various loading, unloading and shearing conditIons were investigated. It was found that the anisotropic structure of tilted microflaps 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. These 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 are intimately coupled to a (also optimum) articulation mechanism. We discuss how both of these features can be simultaneously optimized in the design of robotic systems that can mimic the gecko adhesive system.

JKR Theory for the Stick–Slip Peeling and Adhesion Hysteresis of Gecko Mimetic Patterned Surfaces with a Smooth Glass Surface

“…The 1X flaps showed no measurable adhesion (F ad < 0.1 mN) to the silica surface which is consistent with our previous work ( Figure 4). 11 The graph of apparent area, A app vs the normal actual load, F ⊥ P for the 1X flaps showed no hysteresis between the loading and unloading curves (Figure 4), which is a characteristic signature of nonadhesive contact. This observation is attributed to the high surface roughness (RMS roughness ≈ 250 nm) of the top edge of the 1X flaps (as visualized in the SEM) that reduces the real area of contact between the flaps and the spherical silica surface.…”

“…The full details of the force measurements have been described in previous work. 10,11 As a summary, the spherical glass disc was mounted to the top friction device, which can slide laterally over a distance of 100500 μm at different sliding speeds (110 μm/s). The PDMS flaps were glued to a flat glass disc, which sits on a double cantilever spring with strain gauges that can measure the normal forces.…”

“…10,11,21−30 Previous works have shown that tilted micro structures perform most closely to the gecko adhesive system. 11,12,21,22,31,32 However, little effort has been made to understand the effect of the geometry and the areal density of the flaps at the micro level, which is crucial in determining the contact mechanics of the arrays of the flaps to a surface.…”

Rectangle-capped and tilted micropillar array for enhanced anisotropic anti-shearing in biomimetic adhesion

“…Using this property, they demonstrated sliding of a clean glass surface against and along the tilted microfibres without applying any external normal force and strong anisotropy for shear stresses was observed [17]. Friction and adhesion forces for tilted rectangular flaps were also investigated by Yu et al The structures were found to have strong friction and adhesion forces when sliding along the tilt direction, and low friction and adhesion forces when sliding against the tilt direction [18]. However, these artificial adhesives with inclined micropillars demonstrated a relatively lower magnitude of interfacial friction and adhesion.…”

“…Numerous methods and processes have been reported in literature to emulate this particular anisotropic adhesion produced using inclined micropillar arrays [16][17][18][19][20]. Jin et al studied adhesion and friction properties of micropillar samples at various tilt angles and found that the tilt angle of the micropillars can lead to significant anisotropic friction.…”