Geckos, a type of creatures that can climb rapidly everywhere, have been amazing humans for centuries[1]. It is found that fibrillar structures on their attachment pads allow both strong adhesion and easy release for locomotion[2]. Adhesion in gecko attributed to micro/nano fibrils found on its feet relies on van der Waals forces to adhere to an opposing surface, hence the terminology of dry adhesive[3]. Biological fibrillar dry adhesives have a hierarchical structure closely resembling a tree: the surface of the skin on the animal’s feet is covered in arrays of slender micro-fibrils, each of which supports arrays of fibrils in submicron dimensions[4], Shown in Figure 1. (Images are adapted from Ref. [4].)

Inspired by nature, the dry adhesive concept as seen in climbing lizards especially the gecko has drawn significant interest from researchers. Bioinspired dry adhesives have been developed in research laboratories for more than a decade[3]. In practice, Visco and hyper-elastic materials are often used to achieve the bionic structure and mimic the natural performance[5] (Figure 2; Images are adapted from Ref. [7].) While immense progress has been made in the design and fabrication of multiscale hierarchical adhesive structures in the research domain[6], we highlight the design considerations for the implementation and development in engineering and real application. Therefore, recently we are focusing on the various manufacture procedures for this micro-structure and optimizing the profile to inspire its potential performance, as well as some related work on visual sensor of soft finger.

Figure 1 (Images are adapted from Ref. [4].)

Figure 1 (Images are adapted from Ref. [4].)

Figure 2 (Images are adapted from Ref. [7].)

Figure 2 (Images are adapted from Ref. [7].)

References:

[1] Aristotle. The History of Animals, translated by D’Arcy Wentworth Thompson, n.d.

[2] Boesel L F, Greiner C, Arzt E, et al. Gecko‐inspired surfaces: a path to strong and reversible dry adhesives[J]. Advanced Materials, 2010, 22(19): 2125-2137.

[3] Autumn K, Liang Y A, Hsieh S T, et al. Adhesive force of a single gecko foot-hair[J]. Nature, 2000, 405(6787): 681.

[4] Autumn K, Majidi C, Groff R E, et al. Effective elastic modulus of isolated gecko setal arrays[J]. Journal of Experimental Biology, 2006, 209(18): 3558-3568.

[5] Patil S, Mangal R, Malasi A, et al. Biomimetic wet adhesion of viscoelastic liquid films anchored on micropatterned elastic substrates[J]. Langmuir, 2012, 28(41): 14784-14791.

[6] Sahay R, Low H Y, Baji A, et al. A state-of-the-art review and analysis on the design of dry adhesion materials for applications such as climbing micro-robots[J]. Rsc Advances, 2015, 5(63): 50821-50832.

[7] Hawkes E W, Jiang H, Cutkosky M R. Three-dimensional dynamic surface grasping with dry adhesion[J]. The International Journal of Robotics Research, 2016, 35(8): 943-958.