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Zhang Y, Wan X, Xu X, Teng P, Wang S. Recent progress of tree frog toe pads inspired wet adhesive materials. BIOSURFACE AND BIOTRIBOLOGY 2022. [DOI: 10.1049/bsb2.12049] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
- Yikai Zhang
- Key Laboratory of Bio‐inspired Materials and Interface Science Technical Institute of Physics and Chemistry Chinese Academy of Sciences Beijing China
- University of Chinese Academy of Sciences Beijing China
| | - Xizi Wan
- Key Laboratory of Bio‐inspired Materials and Interface Science Technical Institute of Physics and Chemistry Chinese Academy of Sciences Beijing China
| | - Xuetao Xu
- Key Laboratory of Bio‐inspired Materials and Interface Science Technical Institute of Physics and Chemistry Chinese Academy of Sciences Beijing China
- University of Chinese Academy of Sciences Beijing China
| | - Peicheng Teng
- Key Laboratory of Bio‐inspired Materials and Interface Science Technical Institute of Physics and Chemistry Chinese Academy of Sciences Beijing China
- University of Chinese Academy of Sciences Beijing China
| | - Shutao Wang
- Key Laboratory of Bio‐inspired Materials and Interface Science Technical Institute of Physics and Chemistry Chinese Academy of Sciences Beijing China
- University of Chinese Academy of Sciences Beijing China
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Cai C, Chen Z, Chen Y, Li H, Yang Z, Liu H. Mechanisms and applications of bioinspired underwater/wet adhesives. JOURNAL OF POLYMER SCIENCE 2021. [DOI: 10.1002/pol.20210521] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Chao Cai
- State Key Laboratory of Metal Matrix Composites School of Materials Science and Engineering Shanghai Jiao Tong University Shanghai China
| | - Zhen Chen
- State Key Laboratory of Metal Matrix Composites School of Materials Science and Engineering Shanghai Jiao Tong University Shanghai China
| | - Yujie Chen
- State Key Laboratory of Metal Matrix Composites School of Materials Science and Engineering Shanghai Jiao Tong University Shanghai China
| | - Hua Li
- State Key Laboratory of Metal Matrix Composites School of Materials Science and Engineering Shanghai Jiao Tong University Shanghai China
| | - Zhi Yang
- Department of Oral and Cranio‐maxillofacial Surgery Shanghai Ninth People's Hospital Shanghai Jiao Tong University School of Medicine Shanghai Key Laboratory of Stomatology & Shanghai Research Institute of Stomatology National Clinical Research Center of Stomatology Shanghai China
| | - Hezhou Liu
- State Key Laboratory of Metal Matrix Composites School of Materials Science and Engineering Shanghai Jiao Tong University Shanghai China
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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.
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Chen Z, Chen Y, Hedenqvist MS, Chen C, Cai C, Li H, Liu H, Fu J. Multifunctional conductive hydrogels and their applications as smart wearable devices. J Mater Chem B 2021; 9:2561-2583. [PMID: 33599653 DOI: 10.1039/d0tb02929g] [Citation(s) in RCA: 84] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Recently, hydrogel-based conductive materials and their applications as smart wearable devices have been paid tremendous attention due to their high stretchability, flexibility, and excellent biocompatibility. Compared with single functional conductive hydrogels, multifunctional conductive hydrogels are more advantageous to match various demands for practical applications. This review focuses on multifunctional conductive hydrogels applied for smart wearable devices. Representative strategies for conduction of hydrogels are discussed firstly: (1) electronic conduction based on the conductive fillers and (2) ionic conduction based on charged ions. Then, the common and intensive research on multiple functionalities of conductive hydrogels, such as mechanical properties, conductive and sensory properties, anti-freezing and moisturizing properties, and adhesion and self-healing properties is presented. The applications of multifunctional conductive hydrogels such as in human motion sensors, sensory skins, and personal healthcare diagnosis are provided in the third part. Finally, we offer our perspective on open challenges and future areas of interest for multifunctional conductive hydrogels used as smart wearable devices.
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Affiliation(s)
- Zhen Chen
- State Key Laboratory of Metal Matrix Composites, School of Materials Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, P. R. China.
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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.
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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
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Liu Q, Meng F, Wang X, Yang B, Tan D, Li Q, Shi Z, Shi K, Chen W, Liu S, Lei Y, Xue L. Tree Frog-Inspired Micropillar Arrays with Nanopits on the Surface for Enhanced Adhesion under Wet Conditions. ACS APPLIED MATERIALS & INTERFACES 2020; 12:19116-19122. [PMID: 32216267 DOI: 10.1021/acsami.9b22532] [Citation(s) in RCA: 24] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Inspired by the nanoconcave top of epidermal cells on tree frogs' toe pads, an array of composite micropillars with nanopits on the surface (CPp) has been designed. Polystyrene (PS) nanoparticles are mixed with polydimethylsiloxane (PDMS) and serve as the template for nanopits on the PS/PDMS composite micropillars. CPp shows much larger wet adhesion compared to the arrays of micropillars without nanopits. Under a certain loading force, most of the liquid between CPp and the counterpart surface is squeezed out, so the liquid that remained in nanopits forms multiple nanoscale liquid bridges within the contact area of a single micropillar. Moreover, a large loading force could squeeze part of the liquid out of nanopits, resulting in the suction effect during the pull-off. The multiple liquid bridges, the suction effect, and the solid direct contact thus contribute to strong wet adhesion, which could be ∼36.5 times that of tree frogs' toe pads. The results suggest the function of nanoconcaves on the toe pad of tree frogs and offer a new design strategy for structured adhesives to gain strong wet adhesion.
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Affiliation(s)
- Quan Liu
- School of Power and Mechanical Engineering, The Institute of Technological Science, Wuhan University, South Donghu Road 8, 430072 Wuhan, China
| | - Fandong Meng
- School of Power and Mechanical Engineering, The Institute of Technological Science, Wuhan University, South Donghu Road 8, 430072 Wuhan, China
| | - Xin Wang
- School of Power and Mechanical Engineering, The Institute of Technological Science, Wuhan University, South Donghu Road 8, 430072 Wuhan, China
| | - Baisong Yang
- School of Power and Mechanical Engineering, The Institute of Technological Science, Wuhan University, South Donghu Road 8, 430072 Wuhan, China
| | - Di Tan
- School of Power and Mechanical Engineering, The Institute of Technological Science, Wuhan University, South Donghu Road 8, 430072 Wuhan, China
| | - Qian Li
- School of Power and Mechanical Engineering, The Institute of Technological Science, Wuhan University, South Donghu Road 8, 430072 Wuhan, China
| | - Zhekun Shi
- School of Power and Mechanical Engineering, The Institute of Technological Science, Wuhan University, South Donghu Road 8, 430072 Wuhan, China
| | - Kui Shi
- School of Power and Mechanical Engineering, The Institute of Technological Science, Wuhan University, South Donghu Road 8, 430072 Wuhan, China
| | - Wenhui Chen
- School of Power and Mechanical Engineering, The Institute of Technological Science, Wuhan University, South Donghu Road 8, 430072 Wuhan, China
| | - Sheng Liu
- School of Power and Mechanical Engineering, The Institute of Technological Science, Wuhan University, South Donghu Road 8, 430072 Wuhan, China
| | - Yifeng Lei
- School of Power and Mechanical Engineering, The Institute of Technological Science, Wuhan University, South Donghu Road 8, 430072 Wuhan, China
| | - Longjian Xue
- School of Power and Mechanical Engineering, The Institute of Technological Science, Wuhan University, South Donghu Road 8, 430072 Wuhan, China
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Stark AY, Mitchell CT. Stick or Slip: Adhesive Performance of Geckos and Gecko-Inspired Synthetics in Wet Environments. Integr Comp Biol 2019; 59:214-226. [PMID: 30873552 DOI: 10.1093/icb/icz008] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The gecko adhesive system has inspired hundreds of synthetic mimics principally focused on replicating the strong, reversible, and versatile properties of the natural system. For geckos native to the tropics, versatility includes the need to remain attached to substrates that become wet from high humidity and frequent rain. Paradoxically, van der Waals forces, the principal mechanism responsible for gecko adhesion, reduce to zero when two contacting surfaces separate even slightly by entrapped water layers. A series of laboratory studies show that instead of slipping, geckos maintain and even improve their adhesive performance in many wet conditions (i.e., on wet hydrophobic substrates, on humid substrates held at low temperatures). The mechanism for this is not fully clarified, and likely ranges in scale from the chemical and material properties of the gecko's contact structures called setae (e.g., setae soften and change surface confirmation when exposed to water), to their locomotor biomechanics and decision-making behavior when encountering water on a substrate in their natural environment (e.g., some geckos tend to run faster and stop more frequently on misted substrates than dry). Current work has also focused on applying results from the natural system to gecko-inspired synthetic adhesives, improving their performance in wet conditions. Gecko-inspired synthetic adhesives have also provided a unique opportunity to test hypotheses about the natural system in semi-natural conditions replicated in the laboratory. Despite many detailed studies focused on the role of water and humidity on gecko and gecko-inspired synthetic adhesion, there remains several outstanding questions: (1) what, if any, role does capillary or capillary-like adhesion play on overall adhesive performance of geckos and gecko-inspired synthetics, (2) how do chemical and material changes at the surface and in the bulk of gecko setae and synthetic fibrils change when exposed to water, and what does this mean for adhesive performance, and (3) how much water do geckos encounter in their native environment, and what is their corresponding behavioral response? This review will detail what we know about gecko adhesion in wet environments, and outline the necessary next steps in biological and synthetic system investigations.
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Affiliation(s)
- Alyssa Y Stark
- Department of Biology, Villanova University, 800 East Lancaster Avenue, Villanova, PA 19085, USA
| | - Christopher T Mitchell
- Department of Biology, Villanova University, 800 East Lancaster Avenue, Villanova, PA 19085, USA
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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. 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)'.
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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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Yi H, Lee SH, Seong M, Kwak MK, Jeong HE. Bioinspired reversible hydrogel adhesives for wet and underwater surfaces. J Mater Chem B 2018; 6:8064-8070. [DOI: 10.1039/c8tb02598c] [Citation(s) in RCA: 53] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A hydrogel-based wet adhesive with bioinspired microstructures can exhibit strong and reversible adhesion to wet and underwater surfaces.
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Affiliation(s)
- Hoon Yi
- Department of Mechanical Engineering
- Ulsan National Institute of Science and Technology
- Ulsan 689-798
- Republic of Korea
| | - Sung Ho Lee
- Department of Mechanical Engineering
- Kyungpook National University
- Daegu 702-701
- Republic of Korea
| | - Minho Seong
- Department of Mechanical Engineering
- Ulsan National Institute of Science and Technology
- Ulsan 689-798
- Republic of Korea
| | - Moon Kyu Kwak
- Department of Mechanical Engineering
- Kyungpook National University
- Daegu 702-701
- Republic of Korea
| | - Hoon Eui Jeong
- Department of Mechanical Engineering
- Ulsan National Institute of Science and Technology
- Ulsan 689-798
- Republic of Korea
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