Sticking to the story: outstanding challenges in gecko-inspired adhesives

Abstract

The natural clinging ability of geckos has inspired hundreds of studies seeking design principles that could be applied to creating synthetic adhesives with the same performance capabilities as the gecko: adhesives that use no glue, are self-cleaning and reusable, and are insensitive to a wide range of surface chemistries and roughness. Important progress has been made, and the basic mechanics of how 'hairy' adhesives work have been faithfully reproduced, advancing theory in surface science and portending diverse practical applications. However, after 15 years, no synthetic mimic can yet perform as well as a gecko and simultaneously meet of all the criteria listed above. Moreover, processes for the production of inexpensive and scalable products are still not clearly in view. Here, we discuss our perspective on some of the gaps in understanding that still remain; these gaps in our knowledge should stimulate us to turn to deeper study of the way in which free-ranging geckos stick to the variety of surfaces found in their natural environments and to a more complete analysis of the materials composing the gecko toe pads.

Nonlinear variation in clinging performance with surface roughness in geckos

“…A few recent studies have examined the surface topography of natural substrates and how it affects adhesion in geckos, highlighting the unpredictability (i.e., nonuniform amplitude and wavelengths of asperities creating varying undulance) of natural substrates, especially in comparison with artificial substrates previously used in gecko adhesion studies (Cole, Jones, & Harris, ; Naylor & Higham, ; Russell & Johnson, ; Vanhooydonck et al, ). Other studies have also stressed the importance of using ecologically relevant substrates to better understand performance in insects (Bullock & Federle, ), tree frogs (Langowski et al, ), and geckos (Hagey et al, ; Higham, Russell, Niewiarowski, Wright, & Speck, ; Niewiarowski, Stark, & Dhinojwala, ; Peattie, ). Most recently, Higham et al () summarized the importance, methods, and reasons for including ecological parameters like surface characteristics in gecko adhesion studies.…”

Claw tuft setae of tarantulas (Araneae, Mygalomorphae, Theraphosidae) and the production of fibrous materials. Do tarantulas eject silk from their feet?

“…Most of the 48,231 spider species discovered so far (belonging to 4,140 genera and 119 families) (World Spider Catalog, 2019), belong to the infraorder Araneomorphae (total of 44,656 species). These spiders are equipped with three pairs of spinnerets (ALS + PMS + PLS) and the ability of ALS to produce draglines, fibres which exhibit a unique combination of strength and toughness (Tirell, 1996) and which, given their essential meaning to the life of araneomorphs, are also called lifelines (Osaki, 1996). Anchored to the substratum by attachment discs, the lifeline allows the spider to return safely to the starting point after a thrust at a prey or following a free fall; it also allows spiderlings to maintain contact with the parental web.…”

E2BMO: Facilitating User Interaction with a BioMimetic Ontology via Semantic Translation and Interface Design

“…Gecko toe pads are composed of arrays of hierarchical fibers that make close contact with a surface such that enough van der Waals intermolecular forces can be generated to support the gecko's mass [21][22][23][24][25]. The gecko adhesive system is incredibly multifunctional with properties including reusability, ease of release, underwater adhesion, and self-cleaning [21,[26][27][28]. Materials scientists and biologists alike have been researching this system with a goal of designing and fabricating gecko-like synthetic adhesives that function in a variety of contexts.…”

“…Materials scientists and biologists alike have been researching this system with a goal of designing and fabricating gecko-like synthetic adhesives that function in a variety of contexts. Even so, few synthetic adhesives have been able to fully replicate the multifunctional aspects of the gecko adhesive system and this may be a by-product of not fully understanding how the integrated system operates, as a whole, under a variety of natural conditions [27]. Thus, during functional analysis, it is necessary to consider the particular function of interest within a more systematic context to ensure neither misinterpretation or oversimplification of the abstracted biological principle.…”