Gecko-inspired Structure Research Articles

Fabrication methods of dry adhesive with various shaped microsuction cups

Bio-inspired micro- and nanostructures are emerging as novel dry adhesives owing to their high aspect ratio micropillar structure, resulting in collective van der Waals attraction between the adhesive and the substrate. Specifically, gecko-inspired structures exhibit great adhesive properties on smooth surfaces; however, the pull-off strength of micropillars in gecko-inspired surfaces can be decreased by applying a preloading force. Therefore, octopus suckers or suction cup-like structures have been considered as alternative microstructures providing high adhesion force. The fabrication of both microsuckers and micropillar structures is complicated and requires sophisticated control of the microstructure using photolithography and sequential polymer-based replica molding. Therefore, in this study, a fabrication method for octopus-like and suction cup-like micropatterns on polymer matrix is suggested by simple replica molding using a single master wafer. The relationship between the total adhesion force and the effective surface area of micropatterns was established and calculated by summing the preloading force, the suction force in the normal direction, and the shear force induced by van der Waals attraction. The results of adhesion force measurement and the repeatability test show that the micropatches with square microholes have high adhesion force (16 N/cm2) and good repeatability of attachments/detachments over 100 cycles.

A practical fabrication method of the gecko-inspired easy-removal skin adhesives

Abstract Easy-removal skin adhesives require a robust reversible adhesion. This requirement is addressed in this study with the fabrication of PDMS micro-patterned surfaces that inspired by gecko feet. The design of these gecko-inspired structures were aimed to maximize the ratio between pull-off strength and peel strength. They were fabricated using the laser cutting technology which is typically used for industrial manufacturing applications. Several kinds of PDMS specimens in triangular, square and hexagonal patterns, as well as triangular, square, diamond and circular cross-sections were made. The wetting properties of the gecko-inspired surfaces were evaluated by contact angle measurements. Pull-off strength and peel strength measurements were performed against a silicon skin substitute. Multiple attachments were achieved on a range of preloads. The averaged pull-off strength under a preload 10 N for 10 s can reach up to approximately five times of peel strength when the peel angle is 30 degree. Also compared with conventional Band-Aids, a slight enhancement in attachment ability and a significant decrease in peel strength between the skin and the adhesives were consistently observed. Therefore, the fabrication of the gecko-inspired structures on the micro-molding of PDMS appeared to offer a near-practical way for manufacturing an easy-removal skin adhesives, albeit in its present form with a comparable adhesion strength and a decreased peel strength. The originality of this work is the reverse de-molding approach based on the combination of the cost- and time-efficient laser cutting methods and the Teflon film as the mold material, which avoid the limitation caused by taking PDMS structure out of the molds, so that provide more variations of the tip geometry. As such, a further development of this fabrication method might be of significant interest in a number of practical applications in skin tissue industrial design.

A Gecko-Inspired Robot for Wind Power Tower Inspection

In order to accomplish the task of wind power tower inspection, a heavy-loaded climbing robot inspired by geckos is presented in this paper. The robot not only imitates body’s functions of geckos but also shows a design method. Wind power tower is a conical wall surface and its smallest radius is less than 2m. There will be a great gap when a robot climbing on such wall with small radius. The extraordinary climbing ability of geckos is considered as a remarkable design of nature that is attributed to its soft body, its multi-degree-of-freedom legs, and its strong-adsorbed toes. Focus on the feature of working on such wall surface, gecko’s body, toes and legs are simplified as free joints, magnetic units and redundant tracks respectively, based on the functions of gecko’s limbs and body. The adaptability of the robot is tested by the experiments in laboratory. With the gecko-inspired structure, the robot can climb on the wall surface with minimum 2m in diameter in any direction.

Adhesive Evidence for Gecko-Inspired Biomimetic Fiber: Combination of Experiments and Modeling

A gecko-inspired silicone rubber array was successfully fabricated by ICP etching strategy. Adhesion properties of this gecko-inspired structure were studied through two parallel and independent approaches: experiments and model simulations. In our former work, based on the JKR (Johnson-Kendall-Roberts) contact theory, we proposed a nonlinear mechanical model to formulate the adhesion between a fiber and substrate. Now SPM experimental results verify the maximum adhesion force; show that fiber structure has being relatively better adhesion than unstructured. Moreover, some experimental phenomena explained by our present model.

Adhesive behaviour of gecko-inspired nanofibrillar arrays: combination of experiments and finite element modelling

A polypropylene nanofibrillar array was successfully fabricated by template-assisted nanofabrication strategy. Adhesion properties of this gecko-inspired structure were studied through two parallel and independent approaches: experiments and finite element simulations. Experimental results show relatively good normal adhesion, but accompanied by high preloads. The interfacial adhesion was modelled by effective spring elements with piecewise-linear constitution. The effective elasticity of the fibre-array system was originally calculated from our measured elasticity of single nanowire. Comparisons of the experimental and simulative results reveal quantitative agreement except for some explainable deviations, which suggests the potential applicability of the present models and applied theories.

Directional adhesion of gecko-inspired angled microfiber arrays

Arrays of angled microfibers with a gecko-inspired structure were fabricated from a stiff thermoplastic polymer (polypropylene) with elastic properties similar to those of β-keratin of natural setae. Friction experiments demonstrated that this fibrillar polymer surface exhibits directional adhesion. Sliding of clean glass surfaces against and along the microfiber direction without applying an external normal force produced an apparent shear stress of 0.1 and 4.5 N/cm2, respectively. This directional adhesion is interpreted in the context of a nonlinear elastic bending model of an angled beam. Shearing and normal contact experiments yielded further evidence of the anisotropic adhesion of the fibrillar polymer and revealed the occurrence of a pull-off (adhesive) force at the instant of surface detachment, unlike vertically aligned microfiber arrays of the same material that exhibited a zero pull-off force. The results of this study provide impetus for the design of gecko-inspired adhesives with angled structures that demonstrate directional adhesion against different material surfaces.