The biomimetic replication of dry adhesion present in the gecko's foot has attracted great interest in recent years. All the microfabrication techniques used so far were not able to faithfully reproduce the hierarchical and complex three-dimensional geometry of the gecko's setae, with features at the micro- and nanoscale, thus reducing the effectiveness that such conformal morphology could provide. By means of direct laser lithography we fabricated artificial hairs that faithfully reproduce the natural model. This technique allows the fabrication of three-dimensional microstructures with outstanding results in terms of reproducibility and resolution at the micro- and nanoscale. It was possible to get very close to the morphology of the natural gecko setae, especially concerning the hierarchical shape. We designed several morphologies for the setae and studied the effects in terms of adhesion and friction performances compared to the natural counterpart, showing the interplay between morphology, dimensional scaling and materials. Direct laser lithography promises great applications in the biomimetics field, paving the way to the implementation of the concept of hierarchical bioinspired dry adhesives.

Biomimetics has introduced a new paradigm: by constructing structures with engineered materials and geometries, innovative devices may be fabricated. According to this paradigm, both shape and material properties are equally important to determine functional performance. This idea has been applied also in the field of the microfabrication of smart surfaces, exploiting properties already worked out by nature, like in the case of self-cleaning, drag reduction, structural coloration, and dry adhesion. Regarding dry adhesive properties, geckos represent a good example from which we take inspiration, since they have the extraordinary ability to climb almost every type of surface, even smooth ones, thanks to the hierarchical conformation of the fibrillary setae in their toe pads. Due to this design, they can increase the area of contact with a surface and thus the amount of attractive van der Waals forces. While reproducing with artificial materials the same functional morphology of gecko's pads is typically not achievable with traditional microfabrication techniques, recently Direct Laser Litography offered new opportunities to fabrication of complex three-dimensional structures in the microscale with nanometric resolution. Using direct laser lithography, we have fabricated artificial gecko setae, reproducing with unprecedented faithfulness the natural morphology in the same dimensional scale. Adhesion force of artificial setae toward different surfaces have been tested in dry condition by means of a dedicated setup and compared with natural ones.

Since the discovery of the mechanism of adhesion in geckos, many synthetic dry adhesives have been developed with desirable gecko-like properties such as reusability, directionality, self-cleaning ability, rough surface adhesion and high adhesive stress. However, fully exploiting these adhesives in practical applications at different length scales requires efficient scaling (i.e. with little loss in adhesion as area grows). Just as natural gecko adhesives have been used as a benchmark for synthetic materials, so can gecko adhesion systems provide a baseline for scaling efficiency. In the tokay gecko (Gekko gecko), a scaling power law has been reported relating the maximum shear stress σmax to the area A: σmax ∝ A−1/4. We present a mechanical concept which improves upon the gecko's non-uniform load-sharing and results in a nearly even load distribution over multiple patches of gecko-inspired adhesive. We created a synthetic adhesion system incorporating this concept which shows efficient scaling across four orders of magnitude of area, yielding an improved scaling power law: σmax ∝ A−1/50. Furthermore, we found that the synthetic adhesion system does not fail catastrophically when a simulated failure is induced on a portion of the adhesive. In a practical demonstration, the synthetic adhesion system enabled a 70 kg human to climb vertical glass with 140 cm2 of adhesive per hand.

A synthetic adhesion device is provided that includes a load plate, a load tendon, where the load tendon is connected to the load plate, an array of adhesive tiles, where each the adhesive tile includes adhesion microwedges, an array of degressive elastic elements, where each the degressive elastic element is configured to have a decreasing stiffness with an increasing displacement, where each the degressive elastic element includes a tile tendon, and an array of flexible pedestals, where each the flexible pedestal is connected to the load plate, where each the adhesive tile is connected to the flexible pedestal, where each the adhesive tile is further connected to the tile tendon, where each the degressive elastic element is connected to the load plate, where the array of adhesive tiles are configured for degressive load sharing to all the adhesive tiles.

The adhesive systems of geckos have been widely studied and have been a great source of bioinspiration. Load-sharing (i.e. preventing stress concentrations through equal distribution of loads) is necessary to maximize the performance of an adhesive system, but it is not known to what extent load-sharing occurs in gecko toes. In this paper, we present in vivo measurements of the stress distribution and contact area on the toes of a tokay gecko (Gekko gecko) using a custom tactile sensor with 100 μm spatial resolution. We found that the stress distributions were nonuniform, with large variations in stress between and within lamellae, suggesting that load-sharing in the tokay gecko is uneven. These results may be relevant to the understanding of gecko morphology and the design of improved synthetic adhesive systems.

Pressure and touch sensitivity is crucial for intuitive human‐machine interfaces. Here, we investigate the use of different microstructured elastomers for use as dielectric material in capacitive pressure sensors. We use finite element modeling to simulate how different microstructures can reduce the effective mechanical modulus. We found that pyramidal structures are optimal shapes that reduce the effective mechanical modulus of the elastomer by an order of magnitude. We also investigate the dependence of spacing of the pyramidal microstructures and how it impacts mechanical sensitivity. We further demonstrate the use of these elastomeric microstructures as the dielectric material on a variety of flexible and stretchable substrates to capture touch information in order to enable large area human‐computer interfaces for next generation input devices, as well as continuous health‐monitoring sensors.

Gecko adhesion has inspired climbing robots and synthetic adhesive grippers. Distributing loads between patches of adhesive is important for maximum performance in gecko-inspired devices, but it is unknown how the gecko distributes loads over its toes. We report in vivo measurements of stress distributions on gecko toes. The results are significantly non-uniform.

In this paper, a bioinspired mechanism is presented that allows large patches of directional dry adhesives to attain levels of adhesion previously seen only for small samples in precisely aligned tests. The mechanism uses a rigid tile supported by a compliant material and loaded by an inextensible tendon, and is inspired by the tendon system and the fluid-filled sinus in gecko toes. This mechanism permits the adhesive to make full contact with the surface and have uniform loading despite significant errors in alignment. The single-tile mechanism is demonstrated on the StickybotIII robot and the RiSE climbing robot (gross weight 4 kg). A tiled array of these mechanisms is also presented, with a total adhesive area of 100 cm 2 . This uses a pressurized sac to equalize adhesive forces among the tiles, and exhibits a comparable adhesive pressure and range of loading angles to those of single tiles. These results suggest that the tiled array can be scaled to larger areas and loads.

Directional dry adhesives are inspired by animals such as geckos and are a particularly useful technology for climbing applications. Previously, they have generally been manufactured using photolithographic processes. This paper presents a micro-machining process that involves making cuts in a soft material using a sharp, lubricated tool to create closely spaced negative cavities of a desired shape. The machined material becomes a mold into which an elastomer is cast to create the directional adhesive. The trajectory of the tool can be varied to avoid plastic flow of the mold material that may adversely affect adjacent cavities. The relationship between tool trajectory and resulting cavity shape is established through modeling and process characterization experiments. This micro-machining process is much less expensive than previous photolithographic processes used to create similar features and allows greater flexibility with respect to the micro-scale feature geometry, mold size, and mold material. The micro-machining process produces controllable, directional adhesives, where the normal adhesion increases with shear loading in a preferred direction. This is verified by multi-axis force testing on a flat glass substrate. Upon application of a post-treatment to decrease the roughness of the engaging surfaces of the features after casting, the adhesives significantly outperform comparable directional adhesives made from a photolithographic mold.

Dynamic surface grasping is applicable to landing of micro air vehicles (MAVs) and to grappling objects in space. In both applications, the grasper must absorb the kinetic energy of a moving object and provide secure attachment to a surface using, for example, gecko-inspired directional adhesives. Functional principles of dynamic surface grasping are presented, and two prototype grasper designs are discussed. Computer simulation and physical testing confirms the expected relationships concerning (i) the alignment of the grasper at initial contact, (ii) the absorption of energy during collision and rebound, and (iii) the force limits of synthetic directional adhesives.