scholarly journals A Physical Model Approach to Gecko Adhesion Opportunity and Constraint: How Rough Could It Be?

2019 ◽  
Vol 59 (1) ◽  
pp. 203-213 ◽  
Author(s):  
Peter H Niewiarowski ◽  
Ali Dhinojwala ◽  
Austin M Garner
Keyword(s):  
Adhesive System ◽  
Intermolecular Forces ◽  
Design Parameters ◽  
Substrate Roughness ◽  
Natural Habitats ◽  
Synthetic Adhesives ◽  
Ecological Methods ◽  
And Function ◽  
Gecko Adhesion ◽  
Free Ranging

AbstractIt has been nearly 20 years since Autumn and colleagues established the central role of van der Waals intermolecular forces in how geckos stick. Much has been discovered about the structure and function of fibrillar adhesives in geckos and other taxa, and substantial success has been achieved in translating natural models into bioinspired synthetic adhesives. Nevertheless, synthetics still cannot match the multidimensional performance observed in the natural gecko system that is simultaneously robust to dirt and water, resilient over thousands of cycles, and purportedly competent on surfaces that are rough at drastically different length scales. Apparent insensitivity of adhesion to variability in roughness is particularly interesting from both a theoretical and applied perspective. Progress on understanding the extent to which and the basis of how the gecko adhesive system is robust to variation in roughness is impeded by the complexity of quantifying roughness of natural surfaces and a dearth of data on free-ranging gecko substrate use. Here we review the main challenges in characterizing rough surfaces as they relate to collecting relevant estimates of variation in gecko adhesive performance across different substrates in their natural habitats. In response to these challenges, we propose a practical protocol (borrowing from thermal biophysical ecological methods) that will enable researchers to design detailed studies of structure–function relationships of the gecko fibrillar system. Employing such an approach will help provide specific hypotheses about how adhesive pad structure translates into a capacity for robust gecko adhesion across large variation in substrate roughness. Preliminary data we present on this approach suggest its promise in advancing the study of how geckos deal with roughness variation. We argue and outline how such data can help advance development of design parameters to improve bioinspired adhesives based on the gecko fibrillar system.

scholarly journals Stick or Slip: Adhesive Performance of Geckos and Gecko-Inspired Synthetics in Wet Environments

2019 ◽  
Vol 59 (1) ◽  
pp. 214-226 ◽  
Author(s):  
Alyssa Y Stark ◽  
Christopher T Mitchell
Keyword(s):  
Adhesive System ◽  
Natural System ◽  
Contact Structures ◽  
Principal Mechanism ◽  
Synthetic Adhesives ◽  
Decision Making Behavior ◽  
The Tropics ◽  
Gecko Adhesion ◽  
Adhesive Performance

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.

scholarly journals The Ecomechanics of Gecko Adhesion: Natural Surface Topography, Evolution, and Biomimetics

2019 ◽  
Vol 59 (1) ◽  
pp. 148-167 ◽  
Author(s):  
Timothy E Higham ◽  
Anthony P Russell ◽  
Peter H Niewiarowski ◽  
Amber Wright ◽  
Thomas Speck
Keyword(s):  
Sand Dunes ◽  
Science Research ◽  
Adhesive System ◽  
Microhabitat Use ◽  
Natural Habitats ◽  
Complex Interactions ◽  
Wide Range ◽  
Hierarchical Nature ◽  
Gecko Adhesion ◽  
Adhesive Performance

Abstract The study of gecko adhesion is necessarily interdisciplinary due to the hierarchical nature of the adhesive system and the complexity of interactions between the animals and their habitats. In nature, geckos move on a wide range of surfaces including soft sand dunes, trees, and rocks, but much of the research over the past two decades has focused on their adhesive performance on artificial surfaces. Exploring the complex interactions between geckos and their natural habitats will reveal aspects of the adhesive system that can be applied to biomimetic research, such as the factors that facilitate movement on dirty and rough surfaces with varying microtopography. Additionally, contrasting suites of constraints and topographies are found on rocks and plants, likely driving differences in locomotion and morphology. Our overarching goals are to bring to light several aspects of ecology that are important for gecko–habitat interactions, and to propose a framework for how they can inspire material scientists and functional ecologists. We also present new data on surface roughness and topography of a variety of surfaces, and adhesive performance of Phelsuma geckos on surfaces of varying roughness. We address the following key questions: (1) why and how should ecology be incorporated into the study of gecko adhesion? (2) What topographical features of rocks and plants likely drive adhesive performance? (3) How can ecological studies inform material science research? Recent advances in surface replication techniques that eliminate confounding factors among surface types facilitate the ability to address some of these questions. We pinpoint gaps in our understanding and identify key initiatives that should be adopted as we move forward. Most importantly, fine details of locomotor microhabitat use of both diurnal and nocturnal geckos are needed.

scholarly journals Influence of substrate modulus on gecko adhesion

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Mena R. Klittich ◽  
Michael C. Wilson ◽  
Craig Bernard ◽  
Rochelle M. Rodrigo ◽  
Austin J. Keith ◽  
...  
Keyword(s):  
Biomedical Applications ◽  
Wearable Electronics ◽  
Natural Habitats ◽  
Gekko Gecko ◽  
Dry Adhesion ◽  
Adhesion System ◽  
Synthetic Adhesives ◽  
Influence Of Substrate ◽  
Gecko Adhesion ◽  
First Time

Abstract The gecko adhesion system fascinates biologists and materials scientists alike for its strong, reversible, glue-free, dry adhesion. Understanding the adhesion system’s performance on various surfaces can give clues as to gecko behaviour, as well as towards designing synthetic adhesive mimics. Geckos encounter a variety of surfaces in their natural habitats; tropical geckos, such as Gekko gecko, encounter hard, rough tree trunks as well as soft, flexible leaves. While gecko adhesion on hard surfaces has been extensively studied, little work has been done on soft surfaces. Here, we investigate for the first time the influence of macroscale and nanoscale substrate modulus on whole animal adhesion on two different substrates (cellulose acetate and polydimethylsiloxane) in air and find that across 5 orders of magnitude in macroscale modulus, there is no change in adhesion. On the nanoscale, however, gecko adhesion is shown to depend on substrate modulus. This suggests that low surface-layer modulus may inhibit the gecko adhesion system, independent of other influencing factors such as macroscale composite modulus and surface energy. Understanding the limits of gecko adhesion is vital for clarifying adhesive mechanisms and in the design of synthetic adhesives for soft substrates (including for biomedical applications and wearable electronics).

scholarly journals Setal Field Transects, Evolutionary Transitions and Gecko–Anole Convergence Provide Insights Into the Fundamentals of Form and Function of the Digital Adhesive System of Lizards

2021 ◽  
Vol 6 ◽  
Author(s):  
Anthony P. Russell ◽  
Austin M. Garner
Keyword(s):  
Adhesive System ◽  
Branching Pattern ◽  
Basic Information ◽  
Evolutionary Transitions ◽  
Gekko Gecko ◽  
Form And Function ◽  
Synthetic Adhesives ◽  
Tokay Gecko ◽  
And Function ◽  
Setal Structure

Recent years have witnessed a multitude of studies focusing on gekkotan adhesion. Intense interest in this phenomenon was triggered by the discovery of the manner and magnitude of the forces generated by the hair-like filaments (setae) on the toe pads and inspired the development of the next generation of smart, reversible synthetic adhesives. Most studies pursuing these goals have concentrated on the generalized form and properties of gekkotan setae outlined in those key early studies, resulting in the fabrication of synthetic filaments of uniform dimensions. Although there are over 1,800 species of extant geckos, and hundreds of species of anoles (a separate lizard lineage that has convergently evolved adhesive toe pads), most investigations have used relatively few species as the source of basic information, the Tokay gecko (Gekko gecko) being the most prominent among these. Such exemplar taxa generally exhibit structurally intricate setae and morphologically complex configurations of the adhesive apparatus. Setal structure taken to be characteristic of these taxa is generally reported by singular statements of maximal length, diameter, density and branching pattern. Contemporaneous work focusing on the configuration of setae at locations across the toe pads and upon the evolutionary origin of adhesively competent digits in anoles and specific lineages of geckos, however, has revealed extensive variation of setal structure within individuals, information about how setae may have arisen from non-adhesive filamentous precursors, and how newly adhesively competent digits have been integrated into pre-existing patterns of locomotor mechanics and kinematics. Such observations provide insights into what is minimally necessary for adhesively competent digits to function and reveal the simplest configuration of components that make this possible. We contend that information gleaned from such studies will assist those seeking to employ the principles of fibrillar-based adhesion, as exemplified by lizards, for bio-inspired applications.

Aspects of the Water, Electrolyte and Carbohydrate Physiology of the Silvereye, Zosterops Lateralis (Aves).

1983 ◽  
Vol 31 (5) ◽  
pp. 695 ◽  
Author(s):  
IJ Rooke ◽  
SD Bradshaw ◽  
RA Langworthy
Keyword(s):  
Natural Habitat ◽  
Tritiated Water ◽  
Free Water ◽  
Laboratory Studies ◽  
Turnover Rates ◽  
Natural Habitats ◽  
Water Influx ◽  
Zosterops Lateralis ◽  
Total Body ◽  
Free Ranging

Total body water content (TBW) and TBW turnover were measured by means of tritiated water (HTO) in free-ranging populations of silvereyes, Zosterops lateralis, near Margaret River, W.A. Birds were studied in their natural habitats during spring and summer, and compared with a vineyard population in summer. In the natural habitat TBW content was found to be 77.6% in spring, which was not significantly different from that measured in summer (78.3%). Birds in vineyards in summer, however, were dehydrated, with a TBW content of 69.4%. Calculated rates of water influx for spring, summer and summer vineyards birds were 1.44,2.20 and 0.65 ml g.day-' respectively. These water turnover rates are much higher than those of any other bird yet studied. Dehydration was marked in the vineyard birds, with a significantly lower TBW content and an average net water loss of 0.63 ml day-'. Laboratory studies showed that silvereyes have a low tolerance to sodium loading. Their tolerance is, however, quite adequate for them to drink the most concentrated free water available to them in the field. Ingestion of concentrated sugar solutions of up to 25% did not provoke an osmotic diuresis and thus cannot account for the dehydration and negative water balance of vineyard birds.

scholarly journals Gecko Adhesion in Space and Time: A Phylogenetic Perspective on the Scansorial Success Story

2019 ◽  
Vol 59 (1) ◽  
pp. 117-130 ◽  
Author(s):  
A M Bauer
Keyword(s):  
Structural Diversity ◽  
Adhesive System ◽  
Taxonomic Diversity ◽  
Digital Design ◽  
Morphological Data ◽  
Evolutionary Pathway ◽  
Evolutionary Context ◽  
Phylogenetic Perspective ◽  
And Performance ◽  
Gecko Adhesion

Abstract An evolutionary perspective on gecko adhesion was previously hampered by a lack of an explicit phylogeny for the group and of robust comparative methods to study trait evolution, an underappreciation for the taxonomic and structural diversity of geckos, and a dearth of fossil evidence bearing directly on the origin of the scansorial apparatus. With a multigene dataset as the basis for a comprehensive gekkotan phylogeny, model-based methods have recently been employed to estimate the number of unique derivations of the adhesive system and its role in lineage diversification. Evidence points to a single basal origin of the spinulate oberhautchen layer of the epidermis, which is a necessary precursor for the subsequent elaboration of a functional adhesive mechanism in geckos. However, multiple gains and losses are implicated for the elaborated setae that are necessary for adhesion via van der Waals forces. The well-supported phylogeny of gekkotans has demonstrated that convergence and parallelism in digital design are even more prevalent than previously believed. It also permits the reexamination of previously collected morphological data in an explicitly evolutionary context. Both time-calibrated trees and recently discovered amber fossils that preserve gecko toepads suggest that a fully-functional adhesive apparatus was not only present, but also represented by diverse architectures, by the mid-Cretaceous. Further characterization and phylogenetically-informed analyses of the other components of the adhesive system (muscles, tendons, blood sinuses, etc.) will permit a more comprehensive reconstruction of the evolutionary pathway(s) by which geckos have achieved their structural and taxonomic diversity. A phylogenetic perspective can meaningfully inform functional and performance studies of gecko adhesion and locomotion and can contribute to advances in bioinspired materials.

Intermolecular hydrogen bonding between lipids: influence on organization and function of lipids in membranes

1980 ◽  
Vol 58 (10) ◽  
pp. 755-770 ◽  
Author(s):  
Joan M. Boggs
Keyword(s):  
Hydrogen Bonding ◽  
Phase Separation ◽  
Dynamic Equilibrium ◽  
Hexagonal Phase ◽  
Intermolecular Forces ◽  
Lipid Phase ◽  
Intermolecular Hydrogen Bonding ◽  
Extracellular Stimuli ◽  
And Function ◽  
Lipid Phase Separation

Biological membranes have unique lipid compositions suggesting a specific role for many lipids. Evidence is reviewed concerning the intermolecular forces between glycero- and sphingolipids and cholesterol, the dependence of many of these interactions on the state of ionization of lipids, pH, ionic strength, and divalent cation concentration. The effect of intermolecular interactions between certain lipids on lipid clustering, interaction with cholesterol, on the conformation of proteins, and on transitions to the hexagonal phase is considered. Other forces which cause lipid phase separation or clustering are discussed. It is concluded that lipids are in dynamic equilibrium with their environment and can act as receptors for certain intra- or extracellular stimuli, which they can translate into a response by undergoing changes in fluidity, phase transitions, or phase separation.

Supply chain typology for configuring cost-efficient tracking in fashion logistics

2015 ◽  
Vol 26 (1) ◽  
pp. 42-60 ◽  
Author(s):  
Ville Hinkka ◽  
Maiju Häkkinen ◽  
Jan Holmström ◽  
Kary Främling
Keyword(s):  
Supply Chain ◽  
Supply Chains ◽  
Radio Frequency Identification ◽  
Design Theory ◽  
Design Parameters ◽  
Fashion Industry ◽  
Content Type ◽  
Form And Function ◽  
And Function

Purpose – The purpose of this paper is to propose a typology of radio frequency identification (RFID)-based tracking solution designs to fit differing fashion supply chains. The typology is presented as principles of form and function contributing toward a design theory of configurable RFID tracking for fashion logistics. Design/methodology/approach – The typology is developed based on a case study of a logistics service provider (LSP) interested in designing a tracking solution for different customers in fashion logistics. In addition to the LSP, four fashion retailers were involved in the study. The case study was carried out using a review of existing RFID tracking implementations in the fashion industry, analysis of an RFID tracking pilot conducted by the case company, and interviews with representatives of the retailers. Findings – By varying three design parameters (place of tagging, place of tracking start and place of tracking end) a tracking solution can be configured to fit the requirements and constraints of different fashion supply chains. In the fashion logistics context under investigation, such parameterization addresses retailer requirements, brings concrete and quantifiable benefits to both LSP and its customers, and enables incremental adoption of RFID tracking. Research limitations/implications – Although the typology is developed in the specific setting of a case company developing RFID tracking solutions for fashion logistics, the design parameters identified in the study can be used when considering configurable tracking solutions also in other domains and settings. However, further research is needed to evaluate the proposed typology in those settings. Practical implications – The proposed typology enables fashion companies to consider which configuration of RFID tracking best fits the requirements and constraints imposed by their particular supply chain. For fashion companies, who find adoption of RFID tracking difficult despite the obvious benefits, the proposed typology enables incremental implementation of supply chain-wide tracking. Originality/value – The developed typology, describing how RFID-based tracking solutions can be adjusted to fit the needs of fashion companies with differing supply chains and requirements, is novel. The typology is generalizable to most fashion logistics settings and probably to numerous other logistics domains.

Paper 3: The Future of Packaging Adhesives

1966 ◽  
Vol 181 (5) ◽  
pp. 61-68 ◽  
Author(s):  
C. A. Smith
Keyword(s):  
High Speed ◽  
Adhesive System ◽  
Solid Content ◽  
Design Stage ◽  
Adhesive Systems ◽  
Joint Activities ◽  
Synthetic Materials ◽  
Cellulose Acetates ◽  
Synthetic Adhesives ◽  
Hot Melt

Varying requirements necessitate numerous assembly processes, although all need fluidity which is achieved by a solid being dissolved or dispensed in fluid, or melted. A common adhesive base is a polymer, and more general dispersions are based on polyvinyl acetates; but where speed of assembly and special surfaces are needed, hot melt adhesives are used. Starch pastes and dextrines being ‘natural’ aqueous adhesives are used mainly for bonding non-synthetic porous materials. With the development of cellulose acetates, plastics, polythene, etc., and the introduction of improved machinery, synthetic adhesives became necessary. In view of the fact that hot-melt application appears to be the norm for modern packaging, applications of this type only have been enlarged upon in this paper. As it is essential that adhesive be applied with minimum waste and at a speed regulated to the packaging line there are two main types of applicator, namely, the nozzle type which applies a continuous bead of cement on to a moving web of material and the wheel type which applies a line or pattern of adhesive on to intermittently passing articles by means of a rotating transfer wheel. To arrive at the monetary expenditure it is usual to estimate in terms of milage of seam inches of bond per pound or cost per package unit. Whereas the actual amount of hot melt purchased is usable as an adhesive because it is all solid (although it does yield varying milage), in liquid adhesives the solid content, expressed as a percentage of the total volume, can be quite low. A more important cost factor is the effect of the adhesive system on the production rate of the packaging line—greater efficiency and output offset slightly higher costs. Speed packaging by fully automatic cartoning machines has been introduced and there is a trend for the package to be built around the product, involving joint activities of converter, machinery manufacturer, and adhesive manufacturer all at the same time. This era necessitates high-speed packaging machines together with complete adhesive systems for bonding natural and synthetic materials at high speed. It can be concluded that future packaging adhesives must be fast-setting, have the ability to bond synthetic materials, be automatically fed and applied, be able to withstand exacting service conditions, and adhesive systems must be introduced at the design stage of a new package.

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