The effect of substrate wettability and modulus on gecko and gecko-inspired synthetic adhesion in variable temperature and humidity

Mitchell, Christopher T.; Dayan, Cem Balda; Drotlef, Dirk-M.; Sitti, Metin; Stark, Alyssa Y.

doi:10.1038/s41598-020-76484-6

Cited by 22 publications

(47 citation statements)

References 53 publications

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“…Autumn et al [12] later corroborated Hiller's hypothesis that intermolecular forces governed gecko attachment and provided evidence that van der Waals interactions were the predominant forces involved. Subsequently, other studies have suggested that capillary and electrostatic interactions are also prominent [8][9][10], but whether such forces operate concurrently with van der Waals interactions and under what circumstances particular forces may dominate has received little attention (but see [10]). With regard to setal structure and dimensions, Autumn et al [11] noted that, 'a gecko's foot has nearly five hundred thousand keratinous hairs or setae.…”

Section: Till Present Day: the Interdisciplinary Phasementioning

confidence: 99%

Revisiting the classification of squamate adhesive setae: historical, morphological and functional perspectives

Garner

Russell

2021

R. Soc. open sci.

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Research on gecko-based adhesion has become a truly interdisciplinary endeavour, encompassing many disciplines within the natural and physical sciences. Gecko adhesion occurs by the induction of van der Waals intermolecular (and possibly other) forces between substrata and integumentary filaments (setae) terminating in at least one spatulate tip. Gecko setae have increasingly been idealized as structures with uniform dimensions and a particular branching pattern. Approaches to developing synthetic simulacra have largely adopted such an idealized form as a foundational template. Observations of entire setal fields of geckos and anoles have, however, revealed extensive, predictable variation in setal form. Some filaments of these fields do not fulfil the morphological criteria that characterize setae and, problematically, recent authors have applied the term ‘seta’ to structurally simpler and likely non-adhesively competent fibrils. Herein we briefly review the history of the definition of squamate setae and propose a standardized classificatory scheme for epidermal outgrowths based on a combination of whole animal performance and morphology. Our review is by no means comprehensive of the literature regarding the form, function, and development of the adhesive setae of squamates and we do not address significant advances that have been made in many areas (e.g. cell biology of setae) that are largely tangential to their classification and identification. We contend that those who aspire to simulate the form and function of squamate setae will benefit from a fuller appreciation of the diversity of these structures, thereby assisting in the identification of features most relevant to their objectives.

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Section: Till Present Day: the Interdisciplinary Phasementioning

confidence: 99%

Revisiting the classification of squamate adhesive setae: historical, morphological and functional perspectives

Garner

Russell

2021

R. Soc. open sci.

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“…Geckos navigating their natural habitat may experience one or more of these adhesion‐limiting substrate conditions. For the purpose of this study, we focus on wet substrates that are coated by thin water layers that form as a result of relative humidity (RH), a condition that tropical‐dwelling geckos in particular must mitigate during clinging and running (Mitchell et al, 2020; Niewiarowski et al, 2008; Stark et al, 2012, 2013). Despite the relevance of environmental relative humidity in gecko adhesion, locomotor performance and behavior in variable humidity have never been investigated.…”

Section: Introductionmentioning

confidence: 99%

“…Second, variation in relative humidity may alter adhesive substrate conditions (i.e., thickness of water layer deposited on substrate surface) and/or adhesive material properties (i.e., humidity softens gecko adhesive setae; Prowse et al, 2011; Puthoff et al, 2010; Stark & Mitchell, 2019). Third, there is a complex interaction between ambient temperature and relative humidity in gecko and gecko‐inspired synthetic adhesion (Mitchell et al, 2020; Niewiarowski et al, 2008; Stark & Mitchell, 2019; Stark et al, 2016). Specifically, at 12°C, gecko and gecko‐inspired synthetic adhesion increase as relative humidity increases (30%–80% RH; Mitchell et al, 2020; Niewiarowski et al, 2008; Stark et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

“…Third, there is a complex interaction between ambient temperature and relative humidity in gecko and gecko‐inspired synthetic adhesion (Mitchell et al, 2020; Niewiarowski et al, 2008; Stark & Mitchell, 2019; Stark et al, 2016). Specifically, at 12°C, gecko and gecko‐inspired synthetic adhesion increase as relative humidity increases (30%–80% RH; Mitchell et al, 2020; Niewiarowski et al, 2008; Stark et al, 2016). At 32°C, adhesion is lower, and it peaks between ca.…”

Section: Introductionmentioning

confidence: 99%

“…55% and 70% RH, particularly on a hydrophilic, water layer‐enhancing glass substrate (Figure 1a; Mitchell et al, 2020; Niewiarowski et al, 2008). Two hypotheses have been proposed to explain the role of humidity in gecko adhesive performance: material softening and capillary adhesion (Huber et al, 2005; Prowse et al, 2011; Puthoff et al, 2010; Sun et al, 2005); however, it appears gecko adhesion in variable temperature and humidity is a function of both (Mitchell et al, 2020). On a hydrophilic substrate, capillary adhesion largely dominates, enhancing gecko adhesion (Mitchell et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

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The effect of variable temperature, humidity, and substrate wettability on Gecko (Gekko gecko) locomotor performance and behavior

et al. 2021

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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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Bioinspired Hierarchical Structures for Contact‐Sensible Adhesives

Wang

Tian

et al. 2021

Adv Funct Materials

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Bioinspired structural adhesives that are capable of bonding two objects together have recently found widespread applications in industrial fields, because of their promising reusability and environmental friendliness. However, such adhesives are usually monofunctional and cannot yield real‐time detection on the adhesion status, which is important for both biological systems (e.g., Gecko) and engineered mimics. This study reports a new hierarchical structure with the monolithic integration of adhesion and sensing functions, namely, contact‐sensible adhesive (CSA). The proposed CSA is composed of mushroom‐shaped microstructures on the top layer for providing strong adhesion, and a pillar array sandwiched by a pair of foil electrodes on the bottom layer as a compliant backing and a capacitive sensor. The CSA is not only sensitive to the external pressure, tension, and shear loads, but also shows enhanced adhesion on uneven surfaces, due to the high compliance of the hierarchical system. As a proof of concept, the as‐prepared CSA is applied as a contact interface in a gripper to complete the grasping task.

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The effect of substrate wettability and modulus on gecko and gecko-inspired synthetic adhesion in variable temperature and humidity

Cited by 22 publications

References 53 publications

Revisiting the classification of squamate adhesive setae: historical, morphological and functional perspectives

Revisiting the classification of squamate adhesive setae: historical, morphological and functional perspectives

The effect of variable temperature, humidity, and substrate wettability on Gecko (Gekko gecko) locomotor performance and behavior

Bioinspired Hierarchical Structures for Contact‐Sensible Adhesives

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