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Kumar N, Dalvi S, Sumant AV, Pastewka L, Jacobs TDB, Dhinojwala A. Small-scale roughness entraps water and controls underwater adhesion. SCIENCE ADVANCES 2024; 10:eadn8343. [PMID: 39110787 PMCID: PMC11305375 DOI: 10.1126/sciadv.adn8343] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/02/2024] [Accepted: 07/02/2024] [Indexed: 08/10/2024]
Abstract
While controlling underwater adhesion is critical for designing biological adhesives and in improving the traction of tires, haptics, or adhesives for health monitoring devices, it is hindered by a lack of fundamental understanding of how the presence of trapped water impedes interfacial bonding. Here, by using well-characterized polycrystal diamond surfaces and soft, nonhysteretic, low-surface energy elastomers, we show a reduction in adhesion during approach and four times higher adhesion during retraction as compared to the thermodynamic work of adhesion. Our findings reveal how the loading phase of contact is governed by the entrapment of water by ultrasmall (10-nanometer-scale) surface features. In contrast, the same nanofeatures that reduce adhesion during approach serve to increase adhesion during separation. The explanation for this counterintuitive result lies in the incompressibility-inextensibility of trapped water and the work needed to deform the polymer around water pockets. Unlike the well-known viscoelastic contribution to adhesion, this science unlocks strategies for tailoring surface topography to enhance underwater adhesion.
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Affiliation(s)
- Nityanshu Kumar
- School of Polymer Science and Polymer Engineering, The University of Akron, Akron, OH 44325, USA
| | - Siddhesh Dalvi
- School of Polymer Science and Polymer Engineering, The University of Akron, Akron, OH 44325, USA
| | - Anirudha V. Sumant
- Center for Nanoscale Materials, Argonne National Laboratory, Lemont, IL 60439, USA
| | - Lars Pastewka
- Department of Microsystems Engineering, University of Freiburg, Freiburg 79110, Germany
- Cluster of Excellence livMatS, Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Freiburg 79110, Germany
| | - Tevis D. B. Jacobs
- Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA 15261, USA
| | - Ali Dhinojwala
- School of Polymer Science and Polymer Engineering, The University of Akron, Akron, OH 44325, USA
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2
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Hernandez AM, Sandoval JA, Yuen MC, Wood RJ. Stickiness in shear: stiffness, shape, and sealing in bioinspired suction cups affect shear performance on diverse surfaces. BIOINSPIRATION & BIOMIMETICS 2024; 19:036008. [PMID: 38528733 DOI: 10.1088/1748-3190/ad2c21] [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: 07/26/2023] [Accepted: 02/22/2024] [Indexed: 03/27/2024]
Abstract
Aquatic organisms utilizing attachment often contend with unpredictable environments that can dislodge them from substrates. To counter these forces, many organisms (e.g. fish, cephalopods) have evolved suction-based organs for adhesion. Morphology is diverse, with some disc shapes deviating from a circle to more ovate designs. Inspired by the diversity of multiple aquatic species, we investigated how bioinspired cups with different disc shapes performed in shear loading conditions. These experiments highlighted pertinent physical characteristics found in biological discs (regions of stiffness, flattened margins, a sealing rim), as well as ecologically relevant shearing conditions. Disc shapes of fabricated cups included a standard circle, ellipses, and other bioinspired designs. To consider the effects of sealing, these stiff silicone cups were produced with and without a soft rim. Cups were tested using a force-sensing robotic arm, which directionally sheared them across surfaces of varying roughness and compliance in wet conditions while measuring force. In multiple surface and shearing conditions, elliptical and teardrop shapes outperformed the circle, which suggests that disc shape and distribution of stiffness may play an important role in resisting shear. Additionally, incorporating a soft rim increased cup performance on rougher substrates, highlighting interactions between the cup materials and surfaces asperities. To better understand how these cup designs may resist shear, we also utilized a visualization technique (frustrated total internal reflection; FTIR) to quantify how contact area evolves as the cup is sheared.
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Affiliation(s)
- Alyssa M Hernandez
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Boston, MA, United States of America
- Project CETI, New York, NY 10003 United States of America
| | - Jessica A Sandoval
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Boston, MA, United States of America
- Project CETI, New York, NY 10003 United States of America
| | - Michelle C Yuen
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Boston, MA, United States of America
- Project CETI, New York, NY 10003 United States of America
| | - Robert J Wood
- John A. Paulson School of Engineering and Applied Sciences, Harvard University, Boston, MA, United States of America
- Project CETI, New York, NY 10003 United States of America
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3
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Vallet Y, Laurent C, Bertholdt C, Rahouadj R, Morel O. Analysis of suction-based gripping strategies in wildlife towards future evolutions of the obstetrical suction cup. BIOINSPIRATION & BIOMIMETICS 2022; 17:061003. [PMID: 36206746 DOI: 10.1088/1748-3190/ac9878] [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: 02/10/2022] [Accepted: 10/07/2022] [Indexed: 06/16/2023]
Abstract
The design of obstetrical suction cups used for vacuum assisted delivery has not substantially evolved through history despite of its inherent limitations. The associated challenges concern both the decrease of risk of soft tissue damage and failure of instrumental delivery due to detachment of the cup. The present study firstly details some of the suction-based strategies that have been developed in wildlife in order to create and maintain an adhesive contact with potentially rough and uneven substratum in dry or wet environments. Such strategies have permitted the emergence of bioinspired suction-based devices in the fields of robotics or biomedical patches that are briefly reviewed. The objective is then to extend the observations of such suction-based strategies toward the development of innovative medical suction cups. We firstly conclude that the overall design, shape and materials of the suction cups could be largely improved. We also highlight that the addition of a patterned surface combined with a viscous fluid at the interface between the suction cup and scalp could significantly limit the detachment rate and the differential pressure required to exert a traction force. In the future, the development of a computational model including a detailed description of scalp properties should allow to experiment various designs of bioinspired suction cups.
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Affiliation(s)
- Y Vallet
- CNRS UMR 7239 LEM3-Université de Lorraine, Nancy, France
| | - C Laurent
- CNRS UMR 7239 LEM3-Université de Lorraine, Nancy, France
| | - C Bertholdt
- Université de Lorraine, CHRU-NANCY, Pôle de la Femme, F-54000 Nancy, France
- IADI, INSERM U1254, Rue du Morvan, 54500 Vandoeuvre-lès-Nancy, France
| | - R Rahouadj
- CNRS UMR 7239 LEM3-Université de Lorraine, Nancy, France
| | - O Morel
- Université de Lorraine, CHRU-NANCY, Pôle de la Femme, F-54000 Nancy, France
- IADI, INSERM U1254, Rue du Morvan, 54500 Vandoeuvre-lès-Nancy, France
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4
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Büscher TH, Gorb SN. Convergent Evolution of Adhesive Properties in Leaf Insect Eggs and Plant Seeds: Cross-Kingdom Bioinspiration. Biomimetics (Basel) 2022; 7:biomimetics7040173. [PMID: 36412700 PMCID: PMC9680409 DOI: 10.3390/biomimetics7040173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2022] [Revised: 10/18/2022] [Accepted: 10/20/2022] [Indexed: 12/14/2022] Open
Abstract
Plants and animals are often used as a source for inspiration in biomimetic engineering. However, stronger engagement of biologists is often required in the field of biomimetics. The actual strength of using biological systems as a source of inspiration for human problem solving does not lie in a perfect copy of a single system but in the extraction of core principles from similarly functioning systems that have convergently solved the same problem in their evolution. Adhesive systems are an example of such convergent traits that independently evolved in different organisms. We herein compare two analogous adhesive systems, one from plants seeds and one from insect eggs, to test their properties and functional principles for differences and similarities in order to evaluate the input that can be potentially used for biomimetics. Although strikingly similar, the eggs of the leaf insect Phyllium philippinicum and the seeds of the ivy gourd Coccinia grandis make use of different surface structures for the generation of adhesion. Both employ a water-soluble glue that is spread on the surface via reinforcing fibrous surface structures, but the morphology of these structures is different. In addition to microscopic analysis of the two adhesive systems, we mechanically measured the actual adhesion generated by both systems to quantitatively compare their functional differences on various standardized substrates. We found that seeds can generate much stronger adhesion in some cases but overall provided less reliable adherence in comparison to eggs. Furthermore, eggs performed better regarding repetitive attachment. The similarities of these systems, and their differences resulting from their different purposes and different structural/chemical features, can be informative for engineers working on technical adhesive systems.
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5
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Bergmann JB, Moatsou D, Steiner U, Wilts BD. Bio-inspired materials to control and minimise insect attachment. BIOINSPIRATION & BIOMIMETICS 2022; 17:051001. [PMID: 36099911 DOI: 10.1088/1748-3190/ac91b9] [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: 12/06/2021] [Accepted: 09/13/2022] [Indexed: 06/15/2023]
Abstract
More than three quarters of all animal species on Earth are insects, successfully inhabiting most ecosystems on the planet. Due to their opulence, insects provide the backbone of many biological processes, but also inflict adverse impacts on agricultural and stored products, buildings and human health. To countermeasure insect pests, the interactions of these animals with their surroundings have to be fully understood. This review focuses on the various forms of insect attachment, natural surfaces that have evolved to counter insect adhesion, and particularly features recently developed synthetic bio-inspired solutions. These bio-inspired solutions often enhance the variety of applicable mechanisms observed in nature and open paths for improved technological solutions that are needed in a changing global society.
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Affiliation(s)
- Johannes B Bergmann
- Adolphe Merkle Institute, University of Fribourg, Chemin des Verdiers 4, 1700 Fribourg, Switzerland
| | - Dafni Moatsou
- Institute of Organic Chemistry, Karlsruhe Institute for Technology, Fritz-Haber-Weg 6, 76131 Karlsruhe, Germany
| | - Ullrich Steiner
- Adolphe Merkle Institute, University of Fribourg, Chemin des Verdiers 4, 1700 Fribourg, Switzerland
| | - Bodo D Wilts
- Adolphe Merkle Institute, University of Fribourg, Chemin des Verdiers 4, 1700 Fribourg, Switzerland
- Chemistry and Physics of Materials, University of Salzburg, Jakob-Haringer-Str. 2a, 5020 Salzburg, Austria
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Wang Y, Hensel R, Arzt E. Attachment of bioinspired microfibrils in fluids: transition from a hydrodynamic to hydrostatic mechanism. J R Soc Interface 2022; 19:20220050. [PMID: 35382580 PMCID: PMC8984370 DOI: 10.1098/rsif.2022.0050] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2022] [Accepted: 03/10/2022] [Indexed: 11/12/2022] Open
Abstract
Reversible and switchable adhesion of elastomeric microstructures has attracted significant interest in the development of grippers for object manipulation. Their applications, however, have often been limited to dry conditions and adhesion of such deformable microfibrils in the fluid environment is less understood. In the present study, we performed adhesion tests in silicone oil using single cylindrical microfibrils of a flat-punch shape with a radius of 80 µm. Stiff fibrils were created using three-dimensional printing of an elastomeric resin with an elastic modulus of 500 MPa, and soft fibrils, with a modulus of 3.3 MPa, were moulded in polyurethane. Our results suggest that adhesion is dominated by hydrodynamic forces, which can be maximized by stiff materials and high retraction velocities, in line with theoretical predictions. The maximum pull-off stress of stiff cylindrical fibrils is 0.6 MPa, limited by cavitation and viscous fingering, occurring at retraction velocities greater than 2 µm s-1. Next, we add a mushroom cap to the microfibrils, which, in the case of the softer material, deforms upon retraction and leads to a transition to a hydrostatic suction regime with higher pull-off stresses ranging from 0.7 to 0.9 MPa. The effects of elastic modulus, fibril size and viscosity for underwater applications are illustrated in a mechanism map to provide guidance for design optimization.
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Affiliation(s)
- Yue Wang
- INM – Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
| | - René Hensel
- INM – Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
| | - Eduard Arzt
- INM – Leibniz Institute for New Materials, Campus D2 2, 66123 Saarbrücken, Germany
- Department of Materials Science and Engineering, Saarland University, Campus D2 2, 66123 Saarbrücken, Germany
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7
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Wang Y, Li Z, Elhebeary M, Hensel R, Arzt E, Saif MTA. Water as a "glue": Elasticity-enhanced wet attachment of biomimetic microcup structures. SCIENCE ADVANCES 2022; 8:eabm9341. [PMID: 35319998 PMCID: PMC8942358 DOI: 10.1126/sciadv.abm9341] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Accepted: 01/31/2022] [Indexed: 06/14/2023]
Abstract
Octopus, clingfish, and larva use soft cups to attach to surfaces under water. Recently, various bioinspired cups have been engineered. However, the mechanisms of their attachment and detachment remain elusive. Using a novel microcup, fabricated by two-photon lithography, coupled with in situ pressure sensor and observation cameras, we reveal the detailed nature of its attachment/detachment under water. It involves elasticity-enhanced hydrodynamics generating "self-sealing" and high suction at the cup-substrate interface, converting water into "glue." Detachment is mediated by seal breaking. Three distinct mechanisms of breaking are identified, including elastic buckling of the cup rim. A mathematical model describes the interplay between the attachment/detachment process, geometry, elasto-hydrodynamics, and cup retraction speed. If the speed is too slow, then the octopus cannot attach; if the tide is too gentle for the larva, then water cannot serve as a glue. The concept of "water glue" can innovate underwater transport and manufacturing strategies.
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Affiliation(s)
- Yue Wang
- INM-Leibniz Institute for New Materials, Saarbrücken, Germany
| | - Zhengwei Li
- Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61822, USA
| | - Mohamed Elhebeary
- Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61822, USA
| | - René Hensel
- INM-Leibniz Institute for New Materials, Saarbrücken, Germany
| | - Eduard Arzt
- INM-Leibniz Institute for New Materials, Saarbrücken, Germany
- Saarland University, Materials Science and Engineering, Saarbrücken, Germany
| | - M. Taher A. Saif
- Mechanical Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61822, USA
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8
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Kampowski T, Schuler B, Speck T, Poppinga S. The effects of substrate porosity, mechanical substrate properties and loading conditions on the attachment performance of the Mediterranean medicinal leech ( Hirudo verbana). J R Soc Interface 2022; 19:20220068. [PMID: 35317649 PMCID: PMC8941423 DOI: 10.1098/rsif.2022.0068] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The ectoparasitic lifestyle of the Mediterranean medicinal leech (Hirudo verbana) requires reliable functioning of its attachment organs (i.e. anterior and posterior suction discs) on multiple habitat- and host-specific surfaces under both normal and shear stresses. In addition to some intrinsic properties of the attachment devices, however, only a few extrinsic factors (e.g. substrate roughness and porosity) have been considered in previous studies on leech suckers. Using centrifugal force experiments, we analysed the attachment performance of H. verbana under different types of loading on artificial substrates differing in porosity and their mechanical properties. Whereas the substrate porosity significantly influenced leech attachment under normal and shear loading, the different mechanical properties did not noticeably affect attachment within the considered parameter limits. Furthermore, suction was confirmed to be the primary attachment mechanism independent of the prevailing loading condition. The question of whether the suction cups of H. verbana are adapted to a specific loading condition could not be answered. In any case, our results again highlight the high functional resilience of leech suckers guaranteeing a successful ectoparasitic lifestyle.
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Affiliation(s)
- Tim Kampowski
- Plant Biomechanics Group (PBG), Botanic Garden, University of Freiburg, Schänzlestr. 1, 79104 Freiburg im Breisgau, Germany
- Freiburg Materials Research Center (FMF), University of Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg im Breisgau, Germany
| | - Benedikt Schuler
- Plant Biomechanics Group (PBG), Botanic Garden, University of Freiburg, Schänzlestr. 1, 79104 Freiburg im Breisgau, Germany
| | - Thomas Speck
- Plant Biomechanics Group (PBG), Botanic Garden, University of Freiburg, Schänzlestr. 1, 79104 Freiburg im Breisgau, Germany
- Freiburg Materials Research Center (FMF), University of Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg im Breisgau, Germany
- Cluster of Excellence livMatS@ FIT – Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Georges-Köhler-Allee 105, 79110 Freiburg im Breisgau, Germany
| | - Simon Poppinga
- Plant Biomechanics Group (PBG), Botanic Garden, University of Freiburg, Schänzlestr. 1, 79104 Freiburg im Breisgau, Germany
- Freiburg Materials Research Center (FMF), University of Freiburg, Stefan-Meier-Str. 21, 79104 Freiburg im Breisgau, Germany
- Cluster of Excellence livMatS@ FIT – Freiburg Center for Interactive Materials and Bioinspired Technologies, University of Freiburg, Georges-Köhler-Allee 105, 79110 Freiburg im Breisgau, Germany
- Current address: Botanical Garden, Technical University of Darmstadt, Department of Biology, Schnittspahnstr. 2, 64287 Darmstadt, Germany
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Kang V, White RT, Chen S, Federle W. Extreme suction attachment performance from specialised insects living in mountain streams (Diptera: Blephariceridae). eLife 2021; 10:e63250. [PMID: 34731079 PMCID: PMC8565926 DOI: 10.7554/elife.63250] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2020] [Accepted: 09/24/2021] [Indexed: 01/05/2023] Open
Abstract
Suction is widely used by animals for strong controllable underwater adhesion but is less well understood than adhesion of terrestrial climbing animals. Here we investigate the attachment of aquatic insect larvae (Blephariceridae), which cling to rocks in torrential streams using the only known muscle-actuated suction organs in insects. We measured their attachment forces on well-defined rough substrates and found that their adhesion was less reduced by micro-roughness than that of terrestrial climbing insects. In vivo visualisation of the suction organs in contact with microstructured substrates revealed that they can mould around large asperities to form a seal. We have shown that the ventral surface of the suction disc is covered by dense arrays of microtrichia, which are stiff spine-like cuticular structures that only make tip contact. Our results demonstrate the impressive performance and versatility of blepharicerid suction organs and highlight their potential as a study system to explore biological suction mechanisms.
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Affiliation(s)
- Victor Kang
- Department of Zoology, University of CambridgeCambridgeUnited Kingdom
| | - Robin T White
- Carl Zeiss Research Microscopy SolutionsPleasantonUnited Kingdom
| | - Simon Chen
- Department of Zoology, University of CambridgeCambridgeUnited Kingdom
| | - Walter Federle
- Department of Zoology, University of CambridgeCambridgeUnited Kingdom
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10
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Li S, Liu H, Tian H, Wang C, Wang D, Wu Y, Shao J. Dytiscus lapponicus-Inspired Structure with High Adhesion in Dry and Underwater Environments. ACS APPLIED MATERIALS & INTERFACES 2021; 13:42287-42296. [PMID: 34455771 DOI: 10.1021/acsami.1c13604] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
The epidermal adhesive structure of many animals generates reliable adhesion on their engaged surfaces. However, current bio-inspired adhesion structures are difficult to function well in dry and underwater environments simultaneously. Interestingly, the male Dytiscus lapponicus attaches firmly to the rough shell of the female D. lapponicus in both dry and underwater conditions owing to the adhesive setae of its forelegs, and to the best of our knowledge, designing adhesive structures on multienvironments has never been reported. Here, a D. lapponicus-inspired adhesion structure (DIAS) is proposed and fabricated using double-exposure-fill molding technology accompanied with the material curing shrinkage, in which different structural features could be achieved by varying curing shrinkage ratios, elastic moduli, and back exposure time. The DIAS offered high, reversible, and repeatable strength in dry and underwater conditions with values of 205 and 133 kPa, respectively. By comparing the adhesion properties of different shapes via testing experiments and numerical analysis, a structural feature with an inclination of 15° was found to be optimal. Finally, the potential application of the DIAS in flexible electronic smart skin-attachable devices was demonstrated on a pig skin, paving the way for further bio-inspired adhesive designs for both dry and wet scenarios.
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Affiliation(s)
- Shuai Li
- Micro- and Nano-technology Research Center, State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
| | - Haoran Liu
- Micro- and Nano-technology Research Center, State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
| | - Hongmiao Tian
- Micro- and Nano-technology Research Center, State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
| | - Chunhui Wang
- Micro- and Nano-technology Research Center, State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
| | - Duorui Wang
- Micro- and Nano-technology Research Center, State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
| | - Yihang Wu
- Micro- and Nano-technology Research Center, State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
| | - Jinyou Shao
- Micro- and Nano-technology Research Center, State Key Laboratory for Manufacturing Systems Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, China
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11
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Kang V, Isermann H, Sharma S, Wilson DI, Federle W. How a sticky fluid facilitates prey retention in a carnivorous pitcher plant (Nepenthes rafflesiana). Acta Biomater 2021; 128:357-369. [PMID: 33862281 DOI: 10.1016/j.actbio.2021.04.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2020] [Revised: 03/29/2021] [Accepted: 04/06/2021] [Indexed: 11/29/2022]
Abstract
Nepenthes pitcher plants grow in nutrient-poor soils and produce large pitfall traps to obtain additional nutrients from animal prey. Previous research has shown that the digestive secretion in N. rafflesiana is a sticky viscoelastic fluid that retains insects much more effectively than water, even after significant dilution. Although the retention of prey is known to depend on the fluid's physical properties, the details of how the fluid interacts with insect cuticle and how its sticky nature affects struggling insects are unclear. In this study, we investigated the mechanisms behind the efficient prey retention in N. rafflesiana pitcher fluid. By measuring the attractive forces on insect body parts moved in and out of test fluids, we show that it costs insects more energy to free themselves from pitcher fluid than from water. Moreover, both the maximum force and the energy required for retraction increased after the first contact with the pitcher fluid. We found that insects sink more easily into pitcher fluid than water and, accordingly, the surface tension of N. rafflesiana pitcher fluid was lower than that of water (60.2 vs. 72.3 mN/m). By analysing the pitcher fluid's wetting behaviour, we demonstrate that it strongly resists dewetting from all surfaces tested, leaving behind residual films and filaments that can facilitate re-wetting. This inhibition of dewetting may be a further consequence of the fluid's viscoelastic nature and likely represents a key mechanism underlying prey retention in Nepenthes pitcher plants. STATEMENT OF SIGNIFICANCE: Carnivorous Nepenthes pitcher plants secrete sticky viscoelastic fluids that prevent insects from escaping after falling into the pitcher. What physical mechanisms are responsible for the fluid's retentive function? First, insects sink and drown more readily in N. rafflesiana pitcher fluid due to its reduced surface tension. Second, once within the fluid, our force measurements show that it costs more energy to separate insects from pitcher fluid than from water. Third, the fluid strongly resists dewetting, making it harder for insects to extract themselves and covering their cuticle with residues that facilitate re-wetting. Such striking inhibition of dewetting may represent a previously unrecognised mechanism of prey retention by Nepenthes. Pitcher fluid fulfils a well-defined biological function and may serve as a model for studying the mechanics of complex fluids.
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Affiliation(s)
- Victor Kang
- Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, United Kingdom.
| | - Hauke Isermann
- City University of Applied Sciences Bremen, Neustadtswall 30, 28199 Bremen, Germany
| | - Saksham Sharma
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB3 0AS, United Kingdom
| | - D Ian Wilson
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge CB3 0AS, United Kingdom
| | - Walter Federle
- Department of Zoology, University of Cambridge, Cambridge CB2 3EJ, United Kingdom
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12
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Reversible Underwater Adhesion: The Unique C-shaped Suckers of Net-winged Midge Larvae (Blepharicera sp.). Sci Rep 2020; 10:9395. [PMID: 32523030 PMCID: PMC7286893 DOI: 10.1038/s41598-020-66268-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2019] [Accepted: 05/13/2020] [Indexed: 12/05/2022] Open
Abstract
Aquatic insects living in fast-flowing streams have developed various types of attachment systems to resist being carried away by strong currents. Combinations of various attachment devices offer aquatic insects advantages in underwater adhesion on substrates with different surface properties. In this study, the net-winged midge (Blepharicera sp.) larvae were investigated to understand micro-/nano-structural attachment mechanisms. The hierarchical structure of insect adhesive surfaces was characterized using Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Centrifugal measurements were also conducted to measure the critical rotational velocity at which the larvae of Blepharicera sp. can adhere to substrates with varying roughness. Commercial suckers require smooth substrate surface to maintain a pressure that is lower than the surrounding pressure for adhesion under the sucker cup while the suckers of net-winged midge larvae possess hierarchical micro-/nano-structures, which attach closely to rough surfaces underwater. Furthermore, the functions of microstructures observed on the sucker, including wrinkled surface, inward setae, outer fibers, and nick were explored and may contribute to underwater adhesion. The aligned C-shaped suckers can attach and detach effectively by closing or opening the gap. The unique microstructure and adhesion capability of such suckers could shed light on the design and synthesis of novel bio-inspired devices for reversible underwater adhesion.
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13
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Bressman NR, Armbruster JW, Lujan NK, Udoh I, Ashley‐Ross MA. Evolutionary optimization of an anatomical suction cup: Lip collagen content and its correlation with flow and substrate in Neotropical suckermouth catfishes (Loricarioidei). J Morphol 2020; 281:676-687. [DOI: 10.1002/jmor.21136] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2020] [Revised: 04/13/2020] [Accepted: 04/19/2020] [Indexed: 02/05/2023]
Affiliation(s)
- Noah R. Bressman
- Department of Biology Wake Forest University Winston‐Salem North Carolina USA
| | | | - Nathan K. Lujan
- Department of Ichthyology American Museum of Natural History, New York New York USA
| | - Imoh Udoh
- Department of Biology Wake Forest University Winston‐Salem North Carolina USA
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