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Materzok T, Eslami H, Gorb SN, Müller-Plathe F. Understanding Humidity-Enhanced Adhesion of Geckos: Deep Neural Network-Assisted Multi-Scale Molecular Modeling. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2023; 19:e2206085. [PMID: 36707414 DOI: 10.1002/smll.202206085] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2022] [Revised: 12/06/2022] [Indexed: 06/02/2023]
Abstract
A higher relative humidity leads to an increased sticking power of gecko feet to surfaces. The molecular mechanism responsible for this increase, however, is not clear. Capillary forces, water mediating keratin-surface contacts and water-induced softening of the keratin are proposed as candidates. In previous work, strong evidence for water mediation is found but indirect effects via increased flexibility are not completely ruled out. This article studies the latter hypothesis by a bottom-up coarse-grained mesoscale model of an entire gecko spatula designed without explicit water particles, so that capillary action and water-mediation are excluded. The elasticity of this model is adjusted with a deep neural network to atomistic elastic constants, including water at different concentrations. Our results show clearly that on nanoscopic flat surfaces, the softening of keratin by water uptake cannot nearly account for the experimentally observed increase in gecko sticking power. Here, the dominant mechanism is the mediation of keratin-surface contacts by intervening water molecules. This mechanism remains important on nanostructured surfaces. Here, however, a water-induced increase of the keratin flexibility may enable the spatula to follow surface features smaller than itself and thereby increase the number of contacts with the surface. This leads to an appreciable but not dominant contribution to the humidity-increased adhesion. Recently, by atomistic grand-canonical molecular dynamics simulation, the room-temperature isotherm is obtained for the sorption of water into gecko keratin, to the authors' knowledge, the first such relation for any beta-keratin. In this work, it relates the equilibrium water content of the keratin to the ambient relative humidity.
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Affiliation(s)
- Tobias Materzok
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Profile Area Thermofluids and Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, D-64287, Darmstadt, Germany
| | - Hossein Eslami
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Profile Area Thermofluids and Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, D-64287, Darmstadt, Germany
- Department of Chemistry, Colleges of Sciences, Persian Gulf University, Boushehr, 75168, Iran
| | - Stanislav N Gorb
- Zoological Institute Functional Morphology and Biomechanics, Kiel University, Am Botanischen Garten 1-9, D-24118, Kiel, Germany
| | - Florian Müller-Plathe
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Profile Area Thermofluids and Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, D-64287, Darmstadt, Germany
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2
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Gecko-Inspired Adhesive Mechanisms and Adhesives for Robots—A Review. ROBOTICS 2022. [DOI: 10.3390/robotics11060143] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Small living organisms such as lizards possess naturally built functional surface textures that enable them to walk or climb on versatile surface topographies. Bio-mimicking the surface characteristics of these geckos has enormous potential to improve the accessibility of modern robotics. Therefore, gecko-inspired adhesives have significant industrial applications, including robotic endoscopy, bio-medical cleaning, medical bandage tapes, rock climbing adhesives, tissue adhesives, etc. As a result, synthetic adhesives have been developed by researchers, in addition to dry fibrillary adhesives, elastomeric adhesives, electrostatic adhesives, and thermoplastic adhesives. All these adhesives represent significant contributions towards robotic grippers and gloves, depending on the nature of the application. However, these adhesives often exhibit limitations in the form of fouling, wear, and tear, which restrict their functionalities and load-carrying capabilities in the natural environment. Therefore, it is essential to summarize the state of the art attributes of contemporary studies to extend the ongoing work in this field. This review summarizes different adhesion mechanisms involving gecko-inspired adhesives and attempts to explain the parameters and limitations which have impacts on adhesion. Additionally, different novel adhesive fabrication techniques such as replica molding, 3D direct laser writing, dip transfer processing, fused deposition modeling, and digital light processing are encapsulated.
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Materzok T, Canestraight A, Gorb SN, Müller-Plathe F. How Does Gecko Keratin Stick to Hydrophilic and Hydrophobic Surfaces in the Presence and Absence of Water? An Atomistic Molecular Dynamics Investigation. ACS NANO 2022; 16:19261-19270. [PMID: 36256850 DOI: 10.1021/acsnano.2c08627] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/16/2023]
Abstract
We developed a united-atom model of gecko keratin to investigate the influence of electrostatic and van der Waals contributions to gecko adhesion in scenarios representing gecko's natural habitats. The keratin model assumes that only intrinsically disordered regions directly contact the surface. Contact angles of two generic substrate surfaces that we created match those previously used in AFM experiments on gecko adhesion. Force probe molecular dynamics simulations pulling the keratin from the surface show that the pull-off force increases with increased water content and is inversely related to the water contact angle of the surface. This matches experimental trends. We investigated the number and charge density of keratin and water at the surface, confirming a water-mediating effect and are able to show that keratin folds polar groups to the hydrophilic surface. We decomposed energetic contributions during pull-off, and our computational model shows that in contrast to popular hypotheses, long-range electrostatic interactions determine much of the pull-off process. The contribution of electrostatics to adhesion may be in the order of the van der Waals contributions.
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Affiliation(s)
- Tobias Materzok
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Profile Area Thermofluids and Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Strasse 8, D-64287 Darmstadt, Germany
| | - Annabelle Canestraight
- Department of Chemical Engineering, University of California Santa Barbara, 3357 Engrg II UCSB, Santa Barbara, California 93106, United States
| | - Stanislav N Gorb
- Zoological Institute Functional Morphology and Biomechanics, Kiel University, Am Botanischen Garten 1-9, D-24118 Kiel, Germany
| | - Florian Müller-Plathe
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Profile Area Thermofluids and Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Strasse 8, D-64287 Darmstadt, Germany
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4
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Materzok T, De Boer D, Gorb S, Müller-Plathe F. Gecko Adhesion on Flat and Rough Surfaces: Simulations with a Multi-Scale Molecular Model. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 18:e2201674. [PMID: 35927024 DOI: 10.1002/smll.202201674] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2022] [Revised: 07/07/2022] [Indexed: 06/15/2023]
Abstract
A multiscale modeling approach is used to develop a particle-based mesoscale gecko spatula model that is able to link atomistic simulations and mesoscale (0.44 µm) simulations. It is used to study the detachment of spatulae from flat as well as nanostructured surfaces. The spatula model is based on microscopical information about spatulae structure and on atomistic molecular simulation results. Target properties for the coarse-graining result from a united-atom model of gecko keratin in periodic boundary conditions (PBC), previously developed by the authors. Pull-off forces necessary to detach gecko keratin under 2D PBC parallel to the surface are previously overestimated when only a small region of a spatula is examined. It is shown here that this is due to the restricted geometry (i.e., missing peel-off mode) and not model parameters. The spatula model peels off when pulled away from a surface, both in the molecular picture of the pull-off process and in the force-extension curve of non-equilibrium simulations mimicking single-spatula detachment studied with atomic force microscopy equipment. The force field and spatula model can reproduce experimental pull-off forces. Inspired by experimental results, the underlying mechanism that causes pull-off forces to be at a minimum on surfaces of varying roughnesses is also investigated. A clear sigmoidal increase in the pull-off force of spatulae with surface roughness shows that adhesion is determined by the ratio between spatula pad area and the area between surface peaks. Experiments showed a correlation with root-mean-square roughness of the surface, but the results of this work indicate that this is not a causality but depends on the area accessible.
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Affiliation(s)
- Tobias Materzok
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Profile Area Thermofluids and Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, D-64287, Darmstadt, Germany
| | - Danna De Boer
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Profile Area Thermofluids and Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, D-64287, Darmstadt, Germany
| | - Stanislav Gorb
- Zoological Institute Functional Morphology and Biomechanics, Kiel University, Am Botanischen Garten 1-9, D-24118, Kiel, Germany
| | - Florian Müller-Plathe
- Eduard-Zintl-Institut für Anorganische und Physikalische Chemie and Profile Area Thermofluids and Interfaces, Technische Universität Darmstadt, Alarich-Weiss-Str. 8, D-64287, Darmstadt, Germany
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5
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Zhao K, Liu Y, Ren Y, Li B, Li J, Wang F, Ma C, Ye F, Sun J, Zhang H, Liu K. Molecular Engineered Crown‐Ether‐Protein with Strong Adhesion over a Wide Temperature Range from −196 to 200 °C. Angew Chem Int Ed Engl 2022; 61:e202207425. [DOI: 10.1002/anie.202207425] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Indexed: 12/11/2022]
Affiliation(s)
- Kelu Zhao
- State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry Chinese Academy of Sciences 130022 Changchun China
- University of Science and Technology of China 230026 Hefei China
| | - Yawei Liu
- State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry Chinese Academy of Sciences 130022 Changchun China
| | - Yubin Ren
- Department of Chemistry Tsinghua University 100084 Beijing China
| | - Bo Li
- State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry Chinese Academy of Sciences 130022 Changchun China
| | - Jingjing Li
- State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry Chinese Academy of Sciences 130022 Changchun China
| | - Fan Wang
- State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry Chinese Academy of Sciences 130022 Changchun China
| | - Chao Ma
- Department of Chemistry Tsinghua University 100084 Beijing China
| | - Fangfu Ye
- Beijing National Laboratory for Condensed Matter Physics Institute of Physics Chinese Academy of Sciences Beijing 100190 China
- Wenzhou Institute University of Chinese Academy of Sciences Wenzhou Zhejiang 325001 China
| | - Jing Sun
- East China Normal University China
| | - Hongjie Zhang
- State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry Chinese Academy of Sciences 130022 Changchun China
- University of Science and Technology of China 230026 Hefei China
- Department of Chemistry Tsinghua University 100084 Beijing China
| | - Kai Liu
- State Key Laboratory of Rare Earth Resource Utilization Changchun Institute of Applied Chemistry Chinese Academy of Sciences 130022 Changchun China
- University of Science and Technology of China 230026 Hefei China
- Department of Chemistry Tsinghua University 100084 Beijing China
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6
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Zhao K, Liu Y, Ren Y, Li B, Li J, Wang F, Ma C, Ye F, Sun J, Zhang H, Liu K. Molecular Engineered Crown‐Ether–Protein with Strong Adhesion over a Wide Temperature Range from ‐196 to 200°C. Angew Chem Int Ed Engl 2022. [DOI: 10.1002/ange.202207425] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Kelu Zhao
- Changchun Institute of Applied Chemistry Chinese Academy of Sciences: Chang Chun Institute of Applied Chemistry Chinese Academy of Sciences State Key Laboratory of Rare Earth Resource Utilization CHINA
| | - Yawei Liu
- Changchun Institute of Applied Chemistry Chinese Academy of Sciences: Chang Chun Institute of Applied Chemistry Chinese Academy of Sciences State Key Laboratory of Rare Earth Resource Utilization CHINA
| | - Yubin Ren
- Tsinghua University Department of Chemistry Department of Chemistry CHINA
| | - Bo Li
- Changchun Institute of Applied Chemistry Chinese Academy of Sciences: Chang Chun Institute of Applied Chemistry Chinese Academy of Sciences State Key Laboratory of Rare Earth Resource Utilization CHINA
| | - Jingjing Li
- Changchun Institute of Applied Chemistry Chinese Academy of Sciences: Chang Chun Institute of Applied Chemistry Chinese Academy of Sciences State Key Laboratory of Rare Earth Resource Utilization CHINA
| | - Fan Wang
- Changchun Institute of Applied Chemistry Chinese Academy of Sciences: Chang Chun Institute of Applied Chemistry Chinese Academy of Sciences State Key Laboratory of Rare Earth Resource Utilization 5625 Renmin St, Guilin Road, Chaoyang District 130022 Changchun CHINA
| | - Chao Ma
- Tsinghua University Department of Chemistry CHINA
| | - Fangfu Ye
- Chinese Academy of Sciences Institute of Physics Institute of Physics CHINA
| | - Jing Sun
- Ulm University: Universitat Ulm Institute of Organic Chemistry GERMANY
| | | | - Kai Liu
- Tsinghua University Department of Chemistry qinghua yuan 100084 Beijing CHINA
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7
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Grohmann C, Cohrs AL, Gorb SN. Underwater Attachment of the Water-Lily Leaf Beetle Galerucella nymphaeae (Coleoptera, Chrysomelidae). Biomimetics (Basel) 2022; 7:biomimetics7010026. [PMID: 35225918 PMCID: PMC8883964 DOI: 10.3390/biomimetics7010026] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2022] [Revised: 02/07/2022] [Accepted: 02/11/2022] [Indexed: 11/16/2022] Open
Abstract
While the reversible attachment of artificial structures underwater has moved into the focus of many recent publications, the ability of organisms to walk on and attach to surfaces underwater remains almost unstudied. Here, we describe the behaviour of the water-lily leaf beetle Galerucella nymphaeae when it adheres to surfaces underwater and compare its attachment properties on hydrophilic and hydrophobic surfaces underwater and in the air. The beetles remained attached to horizontal leaves underwater for a few minutes and then detached. When the leaf was inclined, the beetles started to move upward immediately. There was no difference in the size of the tarsal air bubble visible beneath the beetles’ tarsi underwater, between a hydrophilic (54° contact angle of water) and a hydrophobic (99°) surface. The beetles gained the highest traction forces on a hydrophilic surface in the air, the lowest on a hydrophobic surface in air, and intermediate traction on both surfaces underwater. The forces measured on both surfaces underwater did not differ significantly. We discuss factors responsible for the observed effects and conclude that capillary forces on the tarsal air bubble might play a major role in the adhesion to the studied surfaces.
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8
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Park J, Kim Y, Chun B, Seo J. Rational engineering and applications of functional bioadhesives in biomedical engineering. Biotechnol J 2021; 16:e2100231. [PMID: 34469052 DOI: 10.1002/biot.202100231] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2021] [Revised: 08/24/2021] [Accepted: 08/30/2021] [Indexed: 12/31/2022]
Abstract
For the past decades, several bioadhesives have been developed to replace conventional wound closure medical tools such as sutures, staples, and clips. The bioadhesives are easy to use and can minimize tissue damage. They are designed to provide strong adhesion with stable mechanical support on tissue surfaces. However, this monofunctionality of the bioadhesives hinders their practical applications. In particular, a bioadhesive can lose its intended function under harsh tissue environments or delay tissue regeneration during wound healing. Based on several natural and synthetic biomaterials, functional bioadhesives have been developed to overcome the aforementioned limitations. The functional bioadhesives are designed to have specific characteristics such as antimicrobial, cell infiltrative, stimuli-responsive, electrically conductive, and self-healing to ensure stability under harsh tissue conditions, facilitate tissue regeneration, and effectively monitor biosignals. Herein, we thoroughly review the functional bioadhesives from their fundamental background to recent progress with their practical applications for the enhancement of tissue healing and effective biosignal sensing. Furthermore, the future perspectives on the applications of functional bioadhesives and current challenges in their commercialization are also discussed.
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Affiliation(s)
- Jae Park
- Biological Interfaces and Sensor Systems Laboratory, School of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Korea
| | - Yeonju Kim
- Biological Interfaces and Sensor Systems Laboratory, School of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Korea
| | - Beomsoo Chun
- Biological Interfaces and Sensor Systems Laboratory, School of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Korea
| | - Jungmok Seo
- Biological Interfaces and Sensor Systems Laboratory, School of Electrical and Electronic Engineering, Yonsei University, Seoul, Republic of Korea
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9
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Singla S, Jain D, Zoltowski CM, Voleti S, Stark AY, Niewiarowski PH, Dhinojwala A. Direct evidence of acid-base interactions in gecko adhesion. SCIENCE ADVANCES 2021; 7:7/21/eabd9410. [PMID: 34138740 PMCID: PMC8133704 DOI: 10.1126/sciadv.abd9410] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/21/2020] [Accepted: 03/29/2021] [Indexed: 05/06/2023]
Abstract
While it is generally accepted that van der Waals (vdW) forces govern gecko adhesion, several studies indicate contributions from non-vdW forces and highlight the importance of understanding the adhesive contact interface. Previous work hypothesized that the surface of gecko setae is hydrophobic, with nonpolar lipid tails exposed on the surface. However, direct experimental evidence supporting this hypothesis and its implications on the adhesion mechanism is lacking. Here, we investigate the sapphire-setae contact interface using interface-sensitive spectroscopy and provide direct evidence of the involvement of acid-base interactions between polar lipid headgroups exposed on the setal surface and sapphire. During detachment, a layer of unbound lipids is left as a footprint due to cohesive failure within the lipid layer, which, in turn, reduces wear to setae during high stress sliding. The absence of this lipid layer enhances adhesion, despite a small setal-substrate contact area. Our results show that gecko adhesion is not exclusively a vdW-based, residue-free system.
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Affiliation(s)
- Saranshu Singla
- School of Polymer Science and Polymer Engineering, University of Akron, Akron, OH 44325-3909, USA
| | - Dharamdeep Jain
- School of Polymer Science and Polymer Engineering, University of Akron, Akron, OH 44325-3909, USA
| | - Chelsea M Zoltowski
- School of Polymer Science and Polymer Engineering, University of Akron, Akron, OH 44325-3909, USA
| | - Sriharsha Voleti
- School of Polymer Science and Polymer Engineering, University of Akron, Akron, OH 44325-3909, USA
| | - Alyssa Y Stark
- Integrated Bioscience Program, University of Akron, Akron, OH 44325-3908, USA
- Department of Biology, Villanova University, Villanova, PA 19085, USA
| | | | - Ali Dhinojwala
- School of Polymer Science and Polymer Engineering, University of Akron, Akron, OH 44325-3909, USA.
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10
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Ringenwald BE, Bogacki EC, Narvaez CA, Stark AY. The effect of variable temperature, humidity, and substrate wettability on Gecko (Gekko gecko) locomotor performance and behavior. JOURNAL OF EXPERIMENTAL ZOOLOGY PART 2021; 335:454-463. [PMID: 33830673 DOI: 10.1002/jez.2463] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/31/2020] [Revised: 03/17/2021] [Accepted: 03/23/2021] [Indexed: 11/07/2022]
Abstract
Adhesive and locomotor performances of geckos are inherently linked by specialized morphological and biomechanical features. As such, we predict that conditions that lead to poor adhesive performance (i.e., low resistance to applied force while clinging) also lead to poor locomotor performance and behavior (i.e., slowed running speed, increased frequency and duration of stops, more failed or incomplete runs). In this study, we test the prediction that running speed changes as a function of adhesive performance in variable temperature (12 and 32°C), humidity (30, 55, 70, 80% relative humidity), and substrate wettability (hydrophilic glass, intermediately wetting plexiglass). We also expect other locomotor performance traits and behaviors, such as stopping and avoiding treatment conditions, to change as a function of adhesive performance. The results of this study do not fully support our prediction: gecko locomotor performance does not change as a function of humidity or substrate wettability, unlike adhesive performance. As an anticipated result of ectothermy, geckos run significantly slower and stop more frequently and longer at 12°C than 32°C. At high temperature, geckos required significantly more running attempts on hydrophilic glass than plexiglass to complete the experimental procedure, suggesting that this treatment condition is unfavorable. The results of this study highlight the robust locomotive response of geckos to variation in adhesive performance and environmental conditions, and have significant implications for predictions about habitat use and behavior in their natural environment.
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Affiliation(s)
| | - Erin C Bogacki
- Department of Biology, Villanova University, Villanova, Pennsylvania, USA
| | - Carla A Narvaez
- Department of Biology, Villanova University, Villanova, Pennsylvania, USA
| | - Alyssa Y Stark
- Department of Biology, Villanova University, Villanova, Pennsylvania, USA
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11
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Li X, Lai J, Deng Y, Song J, Zhao G, Dong S. Supramolecular Adhesion at Extremely Low Temperatures: A Combined Experimental and Theoretical Investigation. J Am Chem Soc 2020; 142:21522-21529. [PMID: 33301680 DOI: 10.1021/jacs.0c10786] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Adhesive materials that are resistant to low temperatures have wide applications in daily life, scientific research, and industry. Currently, the overwhelming majority of low-temperature-resistant adhesives are traditional polymer systems. In this study, a new strategy was developed to obtain strong and long-lasting adhesion effects from low-molecular-weight adhesives at low temperatures. The introduction of water molecules and the formation of hydrogen bonds not only triggered supramolecular polymerization but also endowed the water-involved copolymer with low-temperature resistance. The water content of the polymeric supramolecular system played a crucial role in exhibiting adhesion behavior at low temperatures. Good adhesion performance was obtained in extremely low-temperature environments, including liquid nitrogen.
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Affiliation(s)
- Xing Li
- College of Chemistry and Chemical Engineering, Hunan University, Changsha, Hunan 410082, P. R. China
| | - Jinlei Lai
- College of Chemistry and Chemical Engineering, Hunan University, Changsha, Hunan 410082, P. R. China
| | - Yan Deng
- College of Chemistry and Chemical Engineering, Hunan University, Changsha, Hunan 410082, P. R. China
| | - Jingfu Song
- State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing, Jiangsu 210016, P. R. China
| | - Gai Zhao
- State Key Laboratory of Mechanics and Control of Mechanical Structures, Nanjing University of Aeronautics and Astronautics, Nanjing, Jiangsu 210016, P. R. China
| | - Shengyi Dong
- College of Chemistry and Chemical Engineering, Hunan University, Changsha, Hunan 410082, P. R. China
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12
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Mitchell CT, Dayan CB, Drotlef DM, Sitti M, Stark AY. The effect of substrate wettability and modulus on gecko and gecko-inspired synthetic adhesion in variable temperature and humidity. Sci Rep 2020; 10:19748. [PMID: 33184356 PMCID: PMC7665207 DOI: 10.1038/s41598-020-76484-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2020] [Accepted: 10/28/2020] [Indexed: 01/23/2023] Open
Abstract
Gecko adhesive performance increases as relative humidity increases. Two primary mechanisms can explain this result: capillary adhesion and increased contact area via material softening. Both hypotheses consider variable relative humidity, but neither fully explains the interactive effects of temperature and relative humidity on live gecko adhesion. In this study, we used live tokay geckos (Gekko gecko) and a gecko-inspired synthetic adhesive to investigate the roles of capillary adhesion and material softening on gecko adhesive performance. The results of our study suggest that both capillary adhesion and material softening contribute to overall gecko adhesion, but the relative contribution of each depends on the environmental context. Specifically, capillary adhesion dominates on hydrophilic substrates, and material softening dominates on hydrophobic substrates. At low temperature (12 °C), both capillary adhesion and material softening likely produce high adhesion across a range of relative humidity values. At high temperature (32 °C), material softening plays a dominant role in adhesive performance at an intermediate relative humidity (i.e., 70% RH).
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Affiliation(s)
- Christopher T Mitchell
- Department of Biology, Villanova University, 800 E. Lancaster Ave., Villanova, PA, 19085, USA
| | - Cem Balda Dayan
- Physical Intelligence Department, Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
| | - Dirk-M Drotlef
- Physical Intelligence Department, Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
| | - Metin Sitti
- Physical Intelligence Department, Max Planck Institute for Intelligent Systems, 70569, Stuttgart, Germany
| | - Alyssa Y Stark
- Department of Biology, Villanova University, 800 E. Lancaster Ave., Villanova, PA, 19085, USA.
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13
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Pillai R, Nordberg E, Riedel J, Schwarzkopf L. Nonlinear variation in clinging performance with surface roughness in geckos. Ecol Evol 2020; 10:2597-2607. [PMID: 32185005 PMCID: PMC7069281 DOI: 10.1002/ece3.6090] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2019] [Revised: 01/20/2020] [Accepted: 01/21/2020] [Indexed: 12/26/2022] Open
Abstract
Understanding the challenges faced by organisms moving within their environment is essential to comprehending the evolution of locomotor morphology and habitat use. Geckos have developed adhesive toe pads that enable exploitation of a wide range of microhabitats. These toe pads, and their adhesive mechanisms, have typically been studied using a range of artificial substrates, usually significantly smoother than those available in nature. Although these studies have been fundamental in understanding the mechanisms of attachment in geckos, it is unclear whether gecko attachment simply gradually declines with increased roughness as some researchers have suggested, or whether the interaction between the gekkotan adhesive system and surface roughness produces nonlinear relationships. To understand ecological challenges faced in their natural habitats, it is essential to use test surfaces that are more like surfaces used by geckos in nature. We tested gecko shear force (i.e., frictional force) generation as a measure of clinging performance on three artificial substrates. We selected substrates that exhibit microtopographies with peak-to-valley heights similar to those of substrates used in nature, to investigate performance on a range of smooth surfaces (glass), and fine-grained (fine sandpaper) to rough (coarse sandpaper). We found that shear force did not decline monotonically with roughness, but varied nonlinearly among substrates. Clinging performance was greater on glass and coarse sandpaper than on fine sandpaper, and clinging performance was not significantly different between glass and coarse sandpaper. Our results demonstrate that performance on different substrates varies, probably depending on the underlying mechanisms of the adhesive apparatus in geckos.
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Affiliation(s)
- Rishab Pillai
- College of Science and EngineeringJames Cook UniversityTownsvilleQLDAustralia
| | - Eric Nordberg
- College of Science and EngineeringJames Cook UniversityTownsvilleQLDAustralia
| | - Jendrian Riedel
- College of Science and EngineeringJames Cook UniversityTownsvilleQLDAustralia
| | - Lin Schwarzkopf
- College of Science and EngineeringJames Cook UniversityTownsvilleQLDAustralia
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14
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Del Grosso CA, Leng C, Zhang K, Hung HC, Jiang S, Chen Z, Wilker JJ. Surface hydration for antifouling and bio-adhesion. Chem Sci 2020; 11:10367-10377. [PMID: 34094298 PMCID: PMC8162394 DOI: 10.1039/d0sc03690k] [Citation(s) in RCA: 68] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Antifouling properties of materials play crucial roles in many important applications such as biomedical implants, marine antifouling coatings, biosensing, and membranes for separation. Poly(ethylene glycol) (or PEG) containing polymers and zwitterionic polymers have been shown to be excellent antifouling materials. It is believed that their outstanding antifouling activity comes from their strong surface hydration. On the other hand, it is difficult to develop underwater glues, although adhesives with strong adhesion in a dry environment are widely available. This is related to dehydration, which is important for adhesion for many cases while water is the enemy of adhesion. In this research, we applied sum frequency generation (SFG) vibrational spectroscopy to investigate buried interfaces between mussel adhesive plaques and a variety of materials including antifouling polymers and control samples, supplemented by studies on marine animal (mussel) behavior and adhesion measurements. It was found that PEG containing polymers and zwitterionic polymers have very strong surface hydration in an aqueous environment, which is the key for their excellent antifouling performance. Because of the strong surface hydration, mussels do not settle on these surfaces even after binding to the surfaces with rubber bands. For control samples, SFG results indicate that their surface hydration is much weaker, and therefore mussels can generate adhesives to displace water to cause dehydration at the interface. Because of the dehydration, mussels can foul on the surfaces of these control materials. Our experiments also showed that if mussels were forced to deposit adhesives onto the PEG containing polymers and zwitterionic polymers, interfacial dehydration did not occur. However, even with the strong interfacial hydration, strong adhesion between mussel adhesives and antifouling polymer surfaces was detected, showing that under certain circumstances, interfacial water could enhance the interfacial bio-adhesion. Antifouling properties of materials play crucial roles in many important applications such as biomedical implants, marine antifouling coatings, biosensing, and membranes for separation.![]()
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Affiliation(s)
| | - Chuan Leng
- Department of Chemistry
- University of Michigan
- Ann Arbor
- USA
| | - Kexin Zhang
- Department of Chemistry
- University of Michigan
- Ann Arbor
- USA
| | - Hsiang-Chieh Hung
- Department of Chemical Engineering
- University of Washington
- Seattle
- USA
| | - Shaoyi Jiang
- Department of Chemical Engineering
- University of Washington
- Seattle
- USA
| | - Zhan Chen
- Department of Chemistry
- University of Michigan
- Ann Arbor
- USA
| | - Jonathan J. Wilker
- Department of Chemistry
- Purdue University
- West Lafayette
- USA
- School of Materials Engineering
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15
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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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16
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Chen P, Li X, Ma J, Zhang R, Qin F, Wang J, Hu TS, Zhang Y, Xu Q. Bioinspired Photodetachable Dry Self-Cleaning Surface. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2019; 35:6379-6386. [PMID: 30990696 DOI: 10.1021/acs.langmuir.8b04310] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Geckos have adapted to the complicated natural environment with its excellent climbing ability. Current artificial gecko-inspired synthetic adhesives (GSAs) mimic gecko's attach-detach mechanism by creating anisotropic and hierarchical structures. Easy detachment and high self-cleaning capability are still the unsolved problems in GSAs. This study presents an unprecedented photodetachable mechanism of making bioinspired smart surfaces utilizing carbon dot (CD)-doped polydimethylsiloxane (PDMS) composites. Under ultraviolet (UV) irradiation, it could be triggered up to 80.46% reduction of adhesion force between PDMS-CDs bioinspired surfaces and contaminating particles. A load-drag-pull (i.e., LDP) test mimicking gecko's locomotion was adopted to test the dry self-cleaning capabilities of these bioinspired surfaces, where the falling rate of the model contaminates (PS micropellets; average size in diameter ∼8 μm) can reach up to 54.83% after seven repeated steps under UV irradiation. The significantly improved dry self-cleaning capability is attributed to the photothermal effect of CDs inside the PDMS matrix. The mechanism proposed in this work will find its applications in the realms of climbing robots, space adhesive devices, and self-cleaning, advanced gripping technologies for pick and place or assembly.
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Affiliation(s)
- Pei Chen
- Institute of Electronics Packaging Technology & Reliability, College of Mechanical Engineering & Applied Electronics Technology , Beijing University of Technology , Beijing 100124 , China
| | - Xudong Li
- Institute of Electronics Packaging Technology & Reliability, College of Mechanical Engineering & Applied Electronics Technology , Beijing University of Technology , Beijing 100124 , China
| | - Junfei Ma
- State Key Laboratory of Petroleum Resources and Prospecting, Harvard SEAS-CUPB Joint Laboratory on Petroleum Science, Beijing Key Laboratory of Biogas Upgrading Utilization , China University of Petroleum , Beijing 102249 , China
| | - Rui Zhang
- State Key Laboratory of Petroleum Resources and Prospecting, Harvard SEAS-CUPB Joint Laboratory on Petroleum Science, Beijing Key Laboratory of Biogas Upgrading Utilization , China University of Petroleum , Beijing 102249 , China
| | - Fei Qin
- Institute of Electronics Packaging Technology & Reliability, College of Mechanical Engineering & Applied Electronics Technology , Beijing University of Technology , Beijing 100124 , China
| | - Jiaojiao Wang
- School of Materials Science and Engineering , East China University of Science and Technology , Shanghai 200237 , China
| | - Travis Shihao Hu
- Department of Mechanical Engineering , California State University , Los Angeles , California 90032 , United States
| | - Yilin Zhang
- C. Eugene Bennett Department of Chemistry , West Virginia University , Morgantown , West Virginia 26506-6045 , United States
| | - Quan Xu
- State Key Laboratory of Petroleum Resources and Prospecting, Harvard SEAS-CUPB Joint Laboratory on Petroleum Science, Beijing Key Laboratory of Biogas Upgrading Utilization , China University of Petroleum , Beijing 102249 , China
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17
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Russell AP, Stark AY, Higham TE. The Integrative Biology of Gecko Adhesion: Historical Review, Current Understanding, and Grand Challenges. Integr Comp Biol 2019; 59:101-116. [DOI: 10.1093/icb/icz032] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
Abstract
Geckos are remarkable in their ability to reversibly adhere to smooth vertical, and even inverted surfaces. However, unraveling the precise mechanisms by which geckos do this has been a long process, involving various approaches over the last two centuries. Our understanding of the principles by which gecko adhesion operates has advanced rapidly over the past 20 years and, with this knowledge, material scientists have attempted to mimic the system to create artificial adhesives. From a biological perspective, recent studies have examined the diversity in morphology, performance, and real-world use of the adhesive apparatus. However, the lack of multidisciplinarity is likely a key roadblock to gaining new insights. Our goals in this paper are to 1) present a historical review of gecko adhesion research, 2) discuss the mechanisms and morphology of the adhesive apparatus, 3) discuss the origin and performance of the system in real-world contexts, 4) discuss advancement in bio-inspired design, and 5) present grand challenges in gecko adhesion research. To continue to improve our understanding, and to more effectively employ the principles of gecko adhesion for human applications, greater intensity and scope of interdisciplinary research are necessary.
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Affiliation(s)
- Anthony P Russell
- Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4
| | - Alyssa Y Stark
- Department of Biology, Villanova University, Villanova, PA 19085, USA
| | - Timothy E Higham
- Department of Evolution, Ecology and Organismal Biology, University of California, Riverside, CA 92521, USA
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18
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Simaite A, Temple B, Amin Karimi M, Alizadehyazdi V, Spenko M. Understanding the influence of silicone elastomer properties on wedge-shaped microstructured dry adhesives loaded in shear. J R Soc Interface 2018; 15:20180551. [PMID: 30232245 PMCID: PMC6170766 DOI: 10.1098/rsif.2018.0551] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Accepted: 08/29/2018] [Indexed: 12/21/2022] Open
Abstract
Anisotropic, gecko-inspired, microstructured adhesives are one of the most promising solutions for many applications in robotics and biomedical applications that require controllable adhesives to grip flat surfaces. In such adhesives, normal adhesion is negligible when loaded solely in the normal direction, but becomes available when the adhesive is loaded in shear first. However, much remains to be learned regarding the friction and failure mechanisms of microstructures loaded in shear. In response, we analysed the load-displacement profiles of wedge-shaped microstructured adhesives comprised of nine different silicone elastomers and their mixtures loaded in shear. The results show that the friction profile depends on at least three factors related to material properties: interfacial adhesion strength in the normal direction (work of separation), elastic modulus and the sample's imperfections (e.g. contamination, misalignment and moulding errors). Moreover, the work of separation influences the maximum friction load such that for materials with the same elastic modulus, the strongest interfacial adhesion yields the lowest friction force. To explain this, we suggest that strongly adhering materials will lead to a macroscopic frictional sliding of the array rather than previously reported stick-slip behaviour.
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Affiliation(s)
- Aiva Simaite
- Mechanical, Materials, and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Brigitte Temple
- Mechanical, Materials, and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Mohammad Amin Karimi
- Mechanical, Materials, and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Vahid Alizadehyazdi
- Mechanical, Materials, and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, IL 60616, USA
| | - Matthew Spenko
- Mechanical, Materials, and Aerospace Engineering Department, Illinois Institute of Technology, Chicago, IL 60616, USA
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19
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Xu Q, Wu X, Wang Z, Hu TS, Street J, Luo Y, Xia Z. Temperature-induced tunable adhesion of gecko setae/spatulae and their biomimics. ACTA ACUST UNITED AC 2018. [DOI: 10.1016/j.matpr.2018.07.109] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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20
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Insights into adhesion of abalone: A mechanical approach. J Mech Behav Biomed Mater 2018; 77:331-336. [DOI: 10.1016/j.jmbbm.2017.09.030] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2017] [Revised: 08/30/2017] [Accepted: 09/21/2017] [Indexed: 11/18/2022]
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21
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Cadirov N, Booth JA, Turner KL, Israelachvili JN. Influence of Humidity on Grip and Release Adhesion Mechanisms for Gecko-Inspired Microfibrillar Surfaces. ACS APPLIED MATERIALS & INTERFACES 2017; 9:14497-14505. [PMID: 28398039 DOI: 10.1021/acsami.7b01624] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Geckos have developed foot pads that allow them to maintain their unique climbing ability despite vast differences of surfaces and environments, from dry desert to humid rainforest. Likewise, successful gecko-inspired mimics should exhibit adhesive and frictional performance across a similarly diverse range of climates. In this work, we focus on the effect of relative humidity (RH) on the "frictional-adhesion" behavior of gecko-inspired adhesive pads. A surface forces apparatus was used to quantitatively measure adhesion and friction forces of a microfibrillar cross-linked polydimethylsiloxane surface against a smooth hemispherical glass disk at varying relative humidity, from 0 to 100% (including fully submerged under water). Geometrically anisotropic tilted half-cylinder microfibers yield a "grip state" (high adhesion and friction forces after shearing along the tilt of the fibers, Fad+ and F∥+) and a "release state" (low adhesion and friction after shearing against the tilt of the fibers, Fad- and F∥-). By appropriate control of the loading path, this allows for transition between strong attachment and easy detachment. Changing the preload and shear direction gives rise to differences in the effective contact area at each fiber and the microscale and nanoscale structure of the contact while changing the relative humidity results in differences in the relative contributions of van der Waals and capillary forces. In combination, both effects lead to interesting trends in the adhesion and friction forces. At up to 75% RH, the grip state adhesion force remains constant and the ratio of grip to release adhesion force does not drop below 4.0. In addition, the friction forces F∥+ and F∥- and the release state adhesion force Fad- exhibit a maximum at intermediate relative humidity between 40% and 75%.
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Affiliation(s)
- Nicholas Cadirov
- Department of Chemical Engineering, and ‡Department of Mechanical Engineering, University of California , Santa Barbara, California 93106, United States
| | - Jamie A Booth
- Department of Chemical Engineering, and ‡Department of Mechanical Engineering, University of California , Santa Barbara, California 93106, United States
| | - Kimberly L Turner
- Department of Chemical Engineering, and ‡Department of Mechanical Engineering, University of California , Santa Barbara, California 93106, United States
| | - Jacob N Israelachvili
- Department of Chemical Engineering, and ‡Department of Mechanical Engineering, University of California , Santa Barbara, California 93106, United States
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