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Meng F, Liu Q, Wang X, Tan D, Xue L, Barnes WJP. Tree frog adhesion biomimetics: opportunities for the development of new, smart adhesives that adhere under wet conditions. Philos Trans A Math Phys Eng Sci 2019; 377:20190131. [PMID: 31177956 PMCID: PMC6562351 DOI: 10.1098/rsta.2019.0131] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Accepted: 04/05/2019] [Indexed: 05/31/2023]
Abstract
Enlarged adhesive toe pads on the tip of each digit allow tree frogs to climb smooth vertical and overhanging surfaces, and are effective in generating reversible adhesion under both dry and wet conditions. In this review, we discuss the complexities of the structure of tree frog toe pads in relation to their function and review their biomimetic potential. Of particular importance are the (largely) hexagonal epithelial cells surrounded by deep channels that cover the surface of each toe pad and the array of nanopillars on their surface. Fluid secreted by the pads covers the surface of each pad, so the pads adhere by wet adhesion, involving both capillarity and viscosity-dependent forces. The fabrication and testing of toe pad mimics are challenging, but valuable both for testing hypotheses concerning tree frog toe pad function and for developing toe pad mimics. Initial mimics involved the fabrication of hexagonal pillars mimicking the toe pad epithelial structure. More recent ones additionally replicate the nanostructures on their surface. Finally we describe some of the biomimetic applications that have been developed from toe pad mimics, which include both bioinspired adhesives and friction-generating devices. This article is part of the theme issue 'Bioinspired materials and surfaces for green science and technology (part 2)'.
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Affiliation(s)
- Fandong Meng
- School of Power and Mechanical Engineering, Wuhan University, South Donghu Road 8, Wuhan, People's Republic of China
| | - Quan Liu
- School of Power and Mechanical Engineering, Wuhan University, South Donghu Road 8, Wuhan, People's Republic of China
| | - Xin Wang
- School of Power and Mechanical Engineering, Wuhan University, South Donghu Road 8, Wuhan, People's Republic of China
| | - Di Tan
- School of Power and Mechanical Engineering, Wuhan University, South Donghu Road 8, Wuhan, People's Republic of China
| | - Longjian Xue
- School of Power and Mechanical Engineering, Wuhan University, South Donghu Road 8, Wuhan, People's Republic of China
| | - W. Jon. P. Barnes
- Centre for Cell Engineering, University of Glasgow, Joseph Black Building, Glasgow G12 8QQ, UK
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Xue L, Sanz B, Luo A, Turner KT, Wang X, Tan D, Zhang R, Du H, Steinhart M, Mijangos C, Guttmann M, Kappl M, del Campo A. Hybrid Surface Patterns Mimicking the Design of the Adhesive Toe Pad of Tree Frog. ACS Nano 2017; 11:9711-9719. [PMID: 28885831 PMCID: PMC5656980 DOI: 10.1021/acsnano.7b04994] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Biological materials achieve directional reinforcement with oriented assemblies of anisotropic building blocks. One such example is the nanocomposite structure of keratinized epithelium on the toe pad of tree frogs, in which hexagonal arrays of (soft) epithelial cells are crossed by densely packed and oriented (hard) keratin nanofibrils. Here, a method is established to fabricate arrays of tree-frog-inspired composite micropatterns composed of polydimethylsiloxane (PDMS) micropillars embedded with polystyrene (PS) nanopillars. Adhesive and frictional studies of these synthetic materials reveal a benefit of the hierarchical and anisotropic design for both adhesion and friction, in particular, at high matrix-fiber interfacial strengths. The presence of PS nanopillars alters the stress distribution at the contact interface of micropillars and therefore enhances the adhesion and friction of the composite micropattern. The results suggest a design principle for bioinspired structural adhesives, especially for wet environments.
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Affiliation(s)
- Longjian Xue
- The Institute
of Technological Science and School of Power and Mechanical Engineering, Wuhan University, South Donghu Road 8, Wuhan 430072, China
- Max-Planck-Institut
für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany
- E-mail for L.X.:
| | - Belén Sanz
- Max-Planck-Institut
für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany
- Instituto
de Ciencia y Tecnología de Polímeros, Consejo Superior de Investigaciones Científicas (CSIC), Juan de la Cierva 3, 28006 Madrid, Spain
| | - Aoyi Luo
- Department
of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, 220 S. 33rd Street, Philadelphia, Pennsylvania 19104-6315, United States
| | - Kevin T. Turner
- Department
of Mechanical Engineering and Applied Mechanics, University of Pennsylvania, 220 S. 33rd Street, Philadelphia, Pennsylvania 19104-6315, United States
| | - Xin Wang
- The Institute
of Technological Science and School of Power and Mechanical Engineering, Wuhan University, South Donghu Road 8, Wuhan 430072, China
| | - Di Tan
- The Institute
of Technological Science and School of Power and Mechanical Engineering, Wuhan University, South Donghu Road 8, Wuhan 430072, China
| | - Rui Zhang
- The Institute
of Technological Science and School of Power and Mechanical Engineering, Wuhan University, South Donghu Road 8, Wuhan 430072, China
| | - Hang Du
- The Institute
of Technological Science and School of Power and Mechanical Engineering, Wuhan University, South Donghu Road 8, Wuhan 430072, China
| | - Martin Steinhart
- Institut
für Chemie neuer Materialien, Universität
Osnabrück, Barbarastr.
7, 49069 Osnabrück, Germany
| | - Carmen Mijangos
- Instituto
de Ciencia y Tecnología de Polímeros, Consejo Superior de Investigaciones Científicas (CSIC), Juan de la Cierva 3, 28006 Madrid, Spain
| | - Markus Guttmann
- Institute
of Microstructure Technology, Karlsruhe
Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
| | - Michael Kappl
- Max-Planck-Institut
für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany
| | - Aránzazu del Campo
- Max-Planck-Institut
für Polymerforschung, Ackermannweg 10, 55128 Mainz, Germany
- INM
− Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
- Chemistry
Department, Saarland University, 66123 Saarbrücken, Germany
- E-mail for A.d.C.:
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Abstract
Attachment devices are essential adaptations for climbing animals and valuable models for synthetic adhesives. A major unresolved question for both natural and bioinspired attachment systems is how attachment performance depends on size. Here, we discuss how contact geometry and mode of detachment influence the scaling of attachment forces for claws and adhesive pads, and how allometric data on biological systems can yield insights into their mechanism of attachment. Larger animals are expected to attach less well to surfaces, due to their smaller surface-to-volume ratio, and because it becomes increasingly difficult to distribute load uniformly across large contact areas. In order to compensate for this decrease of weight-specific adhesion, large animals could evolve overproportionally large pads, or adaptations that increase attachment efficiency (adhesion or friction per unit contact area). Available data suggest that attachment pad area scales close to isometry within clades, but pad efficiency in some animals increases with size so that attachment performance is approximately size-independent. The mechanisms underlying this biologically important variation in pad efficiency are still unclear. We suggest that switching between stress concentration (easy detachment) and uniform load distribution (strong attachment) via shear forces is one of the key mechanisms enabling the dynamic control of adhesion during locomotion.
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Affiliation(s)
- David Labonte
- Department of Zoology, University of Cambridge, Cambridge, UK
| | - Walter Federle
- Department of Zoology, University of Cambridge, Cambridge, UK
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