Gecko-Inspired Combined Lamellar and Nanofibrillar Array for Adhesion on Nonplanar Surface

Lee, Jongho; Bush, Brian G.; Maboudian, Roya; Fearing, Ronald S.

doi:10.1021/la9029672

Cited by 84 publications

(72 citation statements)

References 26 publications

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“…1D and Movie S8, the soft system can increase the adhesion on a highly curved geometry smaller than the FAM and lift up a weight as much as it could with the full contact in Fig. 1 B and C. Unlike geckos' biological foot-hairs, synthetic microfibers are highly sensitive to surface roughness (46), requiring very smooth surfaces like glass for high adhesion. However, the soft system can enhance the weak adhesion of the microfibers on slightly rough surfaces such as cherry tomatoes (Fig.…”

Section: Resultsmentioning

confidence: 99%

Controllable load sharing for soft adhesive interfaces on three-dimensional surfaces

Song

Drotlef

Majidi

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

181

165

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For adhering to three-dimensional (3D) surfaces or objects, current adhesion systems are limited by a fundamental trade-off between 3D surface conformability and high adhesion strength. This limitation arises from the need for a soft, mechanically compliant interface, which enables conformability to nonflat and irregularly shaped surfaces but significantly reduces the interfacial fracture strength. In this work, we overcome this trade-off with an adhesion-based soft-gripping system that exhibits enhanced fracture strength without sacrificing conformability to nonplanar 3D surfaces. Composed of a gecko-inspired elastomeric microfibrillar adhesive membrane supported by a pressure-controlled deformable gripper body, the proposed soft-gripping system controls the bonding strength by changing its internal pressure and exploiting the mechanics of interfacial equal load sharing. The soft adhesion system can use up to ∼26% of the maximum adhesion of the fibrillar membrane, which is 14× higher than the adhering membrane without load sharing. Our proposed load-sharing method suggests a paradigm for soft adhesion-based gripping and transfer-printing systems that achieves area scaling similar to that of a natural gecko footpad.soft gripper | equal load sharing | fracture mechanics | fibrillar adhesives | gecko B y exploiting principles of equal load sharing (1) and interfacial crack pinning (2), geckos' fibrillar foot-hairs can firmly adhere to a wide range of surfaces using intermolecular interactions, such as van der Waals forces (3). Using the same attachment method, gecko-inspired synthetic elastomeric fibrillar adhesives achieve bond strengths of over 100 kPa on smooth flat surfaces (4), surpassing the performance of the gecko on such surfaces (5), and exhibit quick release through peeling (6) or buckling (7) of the microfibers. For the past decade, gecko-inspired adhesives have been applied to a variety of systems including numerous robotic applications for wall climbing (8, 9), perching devices for flyers (10), and grippers (11)(12)(13)(14). However, difficulties arise in dealing with 3D surfaces because the current gecko-inspired synthetic adhesive systems are often supported by a rigid backing, which limits their ability to conform to nonplanar surfaces. In our previous work, we created elastomeric fibrillar adhesives integrated with a soft membrane, which we named as fibrillar adhesives on a membrane (FAM), and fixed the membrane onto a 3D-printed rigid plastic body so that the system could handle various 3D objects (15). Despite demonstrating a significant improvement over an unstructured elastomeric membrane with 10× higher adhesion, the tested FAM could achieve only 2 kPa of adhesion stress, a small fraction of the 55 kPa measured with rigid-backed microfiber arrays (16). This implies that the improved conformability to 3D surfaces enabled by the more compliant membrane backing is at the expense of a 96% reduction in adhesion strength. Considering that the adhesion of a membrane scales with the circumferential ...

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Section: Resultsmentioning

confidence: 99%

Controllable load sharing for soft adhesive interfaces on three-dimensional surfaces

Song

Drotlef

Majidi

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

181

165

View full text Add to dashboard Cite

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“…Current synthetic gecko-inspired adhesives incorporate only micro-and nano-structures that adhere ideally to smooth surfaces, but few synthetic adhesives have incorporated macroscale structures similar to those found on gecko feet that would allow for adhesion on macroscopically rough surfaces (Ge et al, 2007). In one case, Lee et al fabricated nanofiber arrays on lamellae analogues from a hard polymer and demonstrated that adhesion on non-planar surfaces was five times greater than arrays without lamellar support structures (Lee et al, 2009). Our results suggest that adhesion to rough surfaces of these gecko-inspired adhesives may be improved if the relative size between the adhesive geometry and surface geometry is carefully considered.…”

Section: Research Articlementioning

confidence: 99%

Gecko toe and lamellar shear adhesion on macroscopic, engineered rough surfaces

Gillies

Henry

Lin

et al. 2013

Journal of Experimental Biology

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The role in adhesion of the toes and lamellae -intermediate-sized structures -found on the gecko foot remains unclear. Insight into the function of these structures can lead to a more general understanding of the hierarchical nature of the gecko adhesive system, but in particular how environmental topology may relate to gecko foot morphology. We sought to discern the mechanics of the toes and lamellae by examining gecko adhesion on controlled, macroscopically rough surfaces. We used live Tokay geckos, Gekko gecko, to observe the maximum shear force a gecko foot can attain on an engineered substrate constructed with sinusoidal patterns of varying amplitudes and wavelengths in sizes similar to the dimensions of the toes and lamellae structures (0.5 to 6 mm). We found shear adhesion was significantly decreased on surfaces that had amplitudes and wavelengths approaching the lamella length and inter-lamella spacing, losing 95% of shear adhesion over the range tested. We discovered that the toes are capable of adhering to surfaces with amplitudes much larger than their dimensions even without engaging claws, maintaining 60% of shear adhesion on surfaces with amplitudes of 3 mm. Gecko adhesion can be predicted by the ratio of the lamella dimensions to surface feature dimensions. In addition to setae, remarkable macroscopic-scale features of gecko toes and lamellae that include compliance and passive conformation are necessary to maintain contact, and consequently, generate shear adhesion on macroscopically rough surfaces. Findings on the larger scale structures in the hierarchy of gecko foot function could provide the biological inspiration to drive the design of more effective and versatile synthetic fibrillar adhesives.

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“…The incorporation of exclusively 'dry' components , a quick-release mechanism (Russell, 2002), near-indefinite reusability, and self-cleaning (Hansen and Autumn, 2005) make gecko adhesion mechanics interesting not just to researchers in the natural sciences but also to those in engineering disciplines. There are numerous research programs aimed at fabricating gecko-like synthetic adhesives (GSAs) that reproduce the important features of the gecko system Geim et al, 2003;Lee et al, 2009;Mahdavi et al, 2008;Murphy et al, 2007;Sitti and Fearing, 2003).…”

Section: Introductionmentioning

confidence: 99%

Changes in materials properties explain the effects of humidity on gecko adhesion

Puthoff

Prowse

Wilkinson

et al. 2010

Journal of Experimental Biology

143

130

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SUMMARYGeckos owe their remarkable stickiness to millions of dry setae on their toes, and the mechanism of adhesion in gecko setae has been the topic of scientific scrutiny for over two centuries. Previously, we demonstrated that van der Waals forces are sufficient for strong adhesion and friction in gecko setae, and that water-based capillary adhesion is not required. However, recent studies demonstrated that adhesion increases with relative humidity (RH) and proposed that surface hydration and capillary water bridge formation is important or even necessary. In this study, we confirmed a significant effect of RH on gecko adhesion, but rejected the capillary adhesion hypothesis. While contact forces of isolated tokay gecko setal arrays increased with humidity, the increase was similar on hydrophobic and hydrophilic surfaces, inconsistent with a capillary mechanism. Contact forces increased with RH even at high shear rates, where capillary bridge formation is too slow to affect adhesion. How then can a humidity-related increase in adhesion and friction be explained? The effect of RH on the mechanical properties of setal -keratin has escaped consideration until now. We discovered that an increase in RH softens setae and increases viscoelastic damping, which increases adhesion. Changes in setal materials properties, not capillary forces, fully explain humidity-enhanced adhesion, and van der Waals forces remain the only empirically supported mechanism of adhesion in geckos.

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Gecko-Inspired Combined Lamellar and Nanofibrillar Array for Adhesion on Nonplanar Surface

Cited by 84 publications

References 26 publications

Controllable load sharing for soft adhesive interfaces on three-dimensional surfaces

Controllable load sharing for soft adhesive interfaces on three-dimensional surfaces

Gecko toe and lamellar shear adhesion on macroscopic, engineered rough surfaces

Changes in materials properties explain the effects of humidity on gecko adhesion

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