1
|
Glaser NC, Langowski JKA. Stiff skin, soft core: soft backings enhance the conformability and friction of fibre-reinforced adhesives. ROYAL SOCIETY OPEN SCIENCE 2023; 10:221263. [PMID: 36908990 PMCID: PMC9993060 DOI: 10.1098/rsos.221263] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/26/2022] [Accepted: 02/15/2023] [Indexed: 06/18/2023]
Abstract
Biomimetic adhesives with a stiff fibre-reinforced base layer generate strong attachment, even without bioinspired micropatterning of the contact surface. However, current fibre-reinforced adhesive designs are still less versatile with respect to substrate variability than their biological counterparts. In this study, we enhance the comformability of a fibre-reinforced adhesive on curved substrates by adding bioinspired soft backings. We designed and fabricated soft backing variations (polyurethane foams and silicone hydroskeletons) with varying compressive stiffnesses that mimic the soft viscoelastic structures in the adhesive appendages of tree frogs, geckos and other animals. The backings were mounted on a smooth silicone layer enforced with a polyester mesh, and we experimentally investigated the contact area and friction performance of these adhesives on a curved substrate. The results show that the contact area and friction created by a fibre-reinforced adhesive with a soft backing in contact with a non-flat substrate scale inversely with backing stiffness. The integration of stiff fibre-reinforcement with a compressible backing represents an important step in bringing bioinspired adhesives out of the laboratory and into the real world, for example in soft robotic grippers. Moreover, our findings stimulate further research into the role of soft tissues in biological adhesive systems.
Collapse
Affiliation(s)
- Niels C. Glaser
- Department of BioMechanical Engineering, Faculty of Mechanical, Maritime and Materials Engineering, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands
| | - Julian K. A. Langowski
- Experimental Zoology Group, Department of Animal Sciences, Wageningen University and Research, De Elst 1, 6708 WD Wageningen, The Netherlands
| |
Collapse
|
2
|
Tree frog-inspired nanopillar arrays for enhancement of adhesion and friction. Biointerphases 2021; 16:021001. [PMID: 33706530 DOI: 10.1116/6.0000747] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Bioinspired structure adhesives have received increasing interest for many applications, such as climbing robots and medical devices. Inspired by the closely packed keratin nanopillars on the toe pads of tree frogs, tightly arranged polycaprolactone nanorod arrays are prepared by mold process and chemical modification. Nanorod arrays show enhanced adhesion and friction on both smooth and rough surfaces compared to the arrays with hexagonal micropillars. The bonding of nanorods results in a larger stiffness of the nanorod surface, contributing mainly to friction rather than adhesion. The results suggest the function of closely packed keratin nanopillars on the toe pad of tree frogs and offer a guiding principle for the designing of new structured adhesives with strong attaching abilities.
Collapse
|
3
|
Blotto BL, Pereyra MO, Grant T, Faivovich J. Hand and Foot Musculature of Anura: Structure, Homology, Terminology, and Synapomorphies for Major Clades. BULLETIN OF THE AMERICAN MUSEUM OF NATURAL HISTORY 2020. [DOI: 10.1206/0003-0090.443.1.1] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Affiliation(s)
- Boris L. Blotto
- Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, Brazil; División Herpetología, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”–CONICET, Buenos Aires, Argentina
| | - Martín O. Pereyra
- División Herpetología, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”–CONICET, Buenos Aires, Argentina; Laboratorio de Genética Evolutiva “Claudio J. Bidau,” Instituto de Biología Subtropical–CONICET, Facultad de Ciencias Exactas Químic
| | - Taran Grant
- Departamento de Zoologia, Instituto de Biociências, Universidade de São Paulo, São Paulo, Brazil; Coleção de Anfíbios, Museu de Zoologia, Universidade de São Paulo, São Paulo, Brazil; Research Associate, Herpetology, Division of Vertebrate Zoology, A
| | - Julián Faivovich
- División Herpetología, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”–CONICET, Buenos Aires, Argentina; Departamento de Biodiversidad y Biología Experimental, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires, Buenos
| |
Collapse
|
4
|
O'Donnell MK, Deban SM. The Effects of Roughness and Wetness on Salamander Cling Performance. Integr Comp Biol 2020; 60:840-851. [PMID: 32687157 DOI: 10.1093/icb/icaa110] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Animals clinging to natural surfaces have to generate attachment across a range of surface roughnesses in both dry and wet conditions. Plethodontid salamanders can be aquatic, semi-aquatic, terrestrial, arboreal, troglodytic, saxicolous, and fossorial and therefore may need to climb on and over rocks, tree trunks, plant leaves, and stems, as well as move through soil and water. Sixteen species of salamanders were tested to determine the effects of substrate roughness and wetness on maximum cling angle. Substrate roughness had a significant effect on maximum cling angle, an effect that varied among species. Substrates of intermediate roughness (asperity size 100-350 µm) resulted in the poorest attachment performance for all species. Small species performed best on smooth substrates, while large species showed significant improvement on the roughest substrates (asperity size 1000-4000 µm), possibly switching from mucus adhesion on a smooth substrate to an interlocking attachment on rough substrates. Water, in the form of a misted substrate coating and a flowing stream, decreased cling performance in salamanders on smooth substrates. However, small salamanders significantly increased maximum cling angle on wetted substrates of intermediate roughness, compared with the dry condition. Study of cling performance and its relationship to surface properties may cast light onto how this group of salamanders has radiated into the most speciose family of salamanders that occupies diverse habitats across an enormous geographical range.
Collapse
Affiliation(s)
- Mary Kate O'Donnell
- Department of Ecology and Evolutionary Biology, Brown University, 171 Meeting Street, GB 204, Providence, RI 02912, USA; Department of Integrative Biology, University of South Florida, 4202 East Fowler Avenue, SCA 110, Tampa, FL 33620, USA
| | - Stephen M Deban
- Department of Ecology and Evolutionary Biology, Brown University, 171 Meeting Street, GB 204, Providence, RI 02912, USA; Department of Integrative Biology, University of South Florida, 4202 East Fowler Avenue, SCA 110, Tampa, FL 33620, USA
| |
Collapse
|
5
|
Langowski JKA, Dodou D, van Assenbergh P, van Leeuwen JL. Design of Tree-Frog-Inspired Adhesives. Integr Comp Biol 2020; 60:906-918. [PMID: 32413122 PMCID: PMC7751017 DOI: 10.1093/icb/icaa037] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
The adhesive toe pads of tree frogs have inspired the design of various so-called ‘smooth’ synthetic adhesives for wet environments. However, these adhesives do not reach the attachment performance of their biological models in terms of contact formation, maintenance of attachment, and detachment. In tree frogs, attachment is facilitated by an interconnected ensemble of superficial and internal morphological components, which together form a functional unit. To help bridging the gap between biological and bioinspired adhesives, in this review, we (1) provide an overview of the functional components of tree frog toe pads, (2) investigate which of these components (and attachment mechanisms implemented therein) have already been transferred into synthetic adhesives, and (3) highlight functional analogies between existing synthetic adhesives and tree frogs regarding the fundamental mechanisms of attachment. We found that most existing tree-frog-inspired adhesives mimic the micropatterned surface of the ventral epidermis of frog pads. Geometrical and material properties differ between these synthetic adhesives and their biological model, which indicates similarity in appearance rather than function. Important internal functional components such as fiber-reinforcement and muscle fibers for attachment control have not been considered in the design of tree-frog-inspired adhesives. Experimental work on tree-frog-inspired adhesives suggests that the micropatterning of adhesives with low-aspect-ratio pillars enables crack arresting and the drainage of interstitial liquids, which both facilitate the generation of van der Waals forces. Our analysis of experimental work on tree-frog-inspired adhesives indicates that interstitial liquids such as the mucus secreted by tree frogs play a role in detachment. Based on these findings, we provide suggestions for the future design of biomimetic adhesives. Specifically, we propose to implement internal fiber-reinforcements inspired by the fibrous structures in frog pads to create mechanically reinforced soft adhesives for high-load applications. Contractile components may stimulate the design of actuated synthetic adhesives with fine-tunable control of attachment strength. An integrative approach is needed for the design of tree-frog-inspired adhesives that are functionally analogous with their biological paradigm.
Collapse
Affiliation(s)
- Julian K A Langowski
- Experimental Zoology Group, Wageningen University & Research, De Elst 1, Wageningen, 6708 WD, The Netherlands
| | - Dimitra Dodou
- Department of BioMechanical Engineering, Delft University of Technology, Mekelweg 2, Delft, 2628 CD, The Netherlands
| | - Peter van Assenbergh
- Department of BioMechanical Engineering, Delft University of Technology, Mekelweg 2, Delft, 2628 CD, The Netherlands
| | - Johan L van Leeuwen
- Experimental Zoology Group, Wageningen University & Research, De Elst 1, Wageningen, 6708 WD, The Netherlands
| |
Collapse
|
6
|
Federle W, Labonte D. Dynamic biological adhesion: mechanisms for controlling attachment during locomotion. Philos Trans R Soc Lond B Biol Sci 2019; 374:20190199. [PMID: 31495309 PMCID: PMC6745483 DOI: 10.1098/rstb.2019.0199] [Citation(s) in RCA: 30] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 07/23/2019] [Indexed: 01/12/2023] Open
Abstract
The rapid control of surface attachment is a key feature of natural adhesive systems used for locomotion, and a property highly desirable for man-made adhesives. Here, we describe the challenges of adhesion control and the timescales involved across diverse biological attachment systems and different adhesive mechanisms. The most widespread control principle for dynamic surface attachment in climbing animals is that adhesion is 'shear-sensitive' (directional): pulling adhesive pads towards the body results in strong attachment, whereas pushing them away from it leads to easy detachment, providing a rapid mechanical 'switch'. Shear-sensitivity is based on changes of contact area and adhesive strength, which in turn arise from non-adhesive default positions, the mechanics of peeling, pad sliding, and the targeted storage and controlled release of elastic strain energy. The control of adhesion via shear forces is deeply integrated with the climbing animals' anatomy and locomotion, and involves both active neuromuscular control, and rapid passive responses of sophisticated mechanical systems. The resulting dynamic adhesive systems are robust, reliable, versatile and nevertheless remarkably simple. This article is part of the theme issue 'Transdisciplinary approaches to the study of adhesion and adhesives in biological systems'.
Collapse
Affiliation(s)
- Walter Federle
- Department of Zoology, University of Cambridge, Cambridge, UK
| | - David Labonte
- Department of Bioengineering, Imperial College, London, UK
| |
Collapse
|
7
|
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. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 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] [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)'.
Collapse
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
| |
Collapse
|
8
|
Langowski JKA, Singla S, Nyarko A, Schipper H, van den Berg FT, Kaur S, Astley HC, Gussekloo SWS, Dhinojwala A, van Leeuwen JL. Comparative and functional analysis of the digital mucus glands and secretions of tree frogs. Front Zool 2019; 16:19. [PMID: 31210775 PMCID: PMC6563374 DOI: 10.1186/s12983-019-0315-z] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2019] [Accepted: 05/06/2019] [Indexed: 12/18/2022] Open
Abstract
Background Mucus and mucus glands are important features of the amphibian cutis. In tree frogs, the mucus glands and their secretions are crucial components of the adhesive digital pads of these animals. Despite a variety of hypothesised functions of these components in tree frog attachment, the functional morphology of the digital mucus glands and the chemistry of the digital mucus are barely known. Here, we use an interdisciplinary comparative approach to analyse these components, and discuss their roles in tree frog attachment. Results Using synchrotron micro-computer-tomography, we discovered in the arboreal frog Hyla cinerea that the ventral digital mucus glands differ in their morphology from regular anuran mucus glands and form a subdermal gland cluster. We show the presence of this gland cluster also in several other—not exclusively arboreal—anuran families. Using cryo-histochemistry as well as infrared and sum frequency generation spectroscopy on the mucus of two arboreal (H. cinerea and Osteopilus septentrionalis) and of two terrestrial, non-climbing frog species (Pyxicephalus adspersus and Ceratophrys cranwelli), we find neutral and acidic polysaccharides, and indications for proteinaceous and lipid-like mucus components. The mucus chemistry varies only little between dorsal and ventral digital mucus in H. cinerea, ventral digital and abdominal mucus in H. cinerea and O. septentrionalis, and between the ventral abdominal mucus of all four studied species. Conclusions The presence of a digital mucus gland cluster in various anuran families, as well as the absence of differences in the mucus chemistry between arboreal and non-arboreal frog species indicate an adaptation towards generic functional requirements as well as to attachment-related requirements. Overall, this study contributes to the understanding of the role of glands and their secretions in tree frog attachment and in bioadhesion in general, as well as the evolution of anurans. Electronic supplementary material The online version of this article (10.1186/s12983-019-0315-z) contains supplementary material, which is available to authorized users.
Collapse
Affiliation(s)
- Julian K A Langowski
- 1Experimental Zoology Group, Department of Animal Sciences, Wageningen University & Research, De Elst 1, Wageningen, 6708 WD The Netherlands
| | - Saranshu Singla
- 2Department of Polymer Science, The University of Akron, 170 University Ave, Akron, Ohio 44325-3909 USA
| | - Alex Nyarko
- 2Department of Polymer Science, The University of Akron, 170 University Ave, Akron, Ohio 44325-3909 USA
| | - Henk Schipper
- 1Experimental Zoology Group, Department of Animal Sciences, Wageningen University & Research, De Elst 1, Wageningen, 6708 WD The Netherlands
| | - Frank T van den Berg
- 1Experimental Zoology Group, Department of Animal Sciences, Wageningen University & Research, De Elst 1, Wageningen, 6708 WD The Netherlands
| | - Sukhmanjot Kaur
- 2Department of Polymer Science, The University of Akron, 170 University Ave, Akron, Ohio 44325-3909 USA
| | - Henry C Astley
- 3Biomimicry Research & Innovation Center, Departments of Biology and Polymer Science, The University of Akron, 235 Carroll St., Akron, Ohio 44325-3908 USA
| | - Sander W S Gussekloo
- 1Experimental Zoology Group, Department of Animal Sciences, Wageningen University & Research, De Elst 1, Wageningen, 6708 WD The Netherlands
| | - Ali Dhinojwala
- 2Department of Polymer Science, The University of Akron, 170 University Ave, Akron, Ohio 44325-3909 USA
| | - Johan L van Leeuwen
- 1Experimental Zoology Group, Department of Animal Sciences, Wageningen University & Research, De Elst 1, Wageningen, 6708 WD The Netherlands
| |
Collapse
|
9
|
Langowski JKA, Rummenie A, Pieters RPM, Kovalev A, Gorb SN, van Leeuwen JL. Estimating the maximum attachment performance of tree frogs on rough substrates. BIOINSPIRATION & BIOMIMETICS 2019; 14:025001. [PMID: 30706849 DOI: 10.1088/1748-3190/aafc37] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
Abstract
Tree frogs can attach to smooth and rough substrates using their adhesive toe pads. We present the results of an experimental investigation of tree frog attachment to rough substrates, and of the role of mechanical interlocking between superficial toe pad structures and substrate asperities in the tree frog species Litoria caerulea and Hyla cinerea. Using a rotation platform setup, we quantified the adhesive and frictional attachment performance of whole frogs clinging to smooth, micro-, and macrorough substrates. The transparent substrates enabled quantification of the instantaneous contact area during detachment by using frustrated total internal reflection. A linear mixed-effects model shows that the adhesive performance of the pads does not differ significantly with roughness (for nominal roughness levels of 0-15 µm) in both species. This indicates that mechanical interlocking does not contribute to the attachment of whole animals. Our results show that the adhesion performance of tree frogs is higher than reported previously, emphasising the biomimetic potential of tree frog attachment. Overall, our findings contribute to a better understanding of the complex interplay of attachment mechanisms in the toe pads of tree frogs, which may promote future designs of tree-frog-inspired adhesives.
Collapse
Affiliation(s)
- Julian K A Langowski
- Experimental Zoology Group, Wageningen University & Research, Wageningen, The Netherlands
| | | | | | | | | | | |
Collapse
|