Roles of discontinuities in bio-inspired adhesive pads

Chung, Jun Young; Chaudhury, Manoj K.

doi:10.1098/rsif.2004.0020

Cited by 185 publications

(169 citation statements)

References 21 publications

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“…Note in Fig. 5B that voids do in fact nucleate ahead of the opening crack tip in several instances, as is the case with thin soft films in confined geometry (40,41). Failure by void nucleation represents the maximum enhancement possible by the mechanism proposed here and is limited by individual fibril detachments, a situation that has been studied in detail elsewhere (21,30).…”

Section: Resultsmentioning

confidence: 90%

“…Failure by void nucleation represents the maximum enhancement possible by the mechanism proposed here and is limited by individual fibril detachments, a situation that has been studied in detail elsewhere (21,30). Before concluding, it should be noted that crack arrest and re-initiation have been observed to enhance adhesion, even in nonfibrillar systems (40)(41)(42)(43). These cases involve incisions in thin confined films (40,41), discontinuity of film thickness (42,43), and the discontinuity of the elastic modulii of adjoining films (42).…”

Section: Resultsmentioning

confidence: 99%

“…Before concluding, it should be noted that crack arrest and re-initiation have been observed to enhance adhesion, even in nonfibrillar systems (40)(41)(42)(43). These cases involve incisions in thin confined films (40,41), discontinuity of film thickness (42,43), and the discontinuity of the elastic modulii of adjoining films (42). It may be possible to develop a unifying description of the enhancement of fracture toughness in these related systems by using the picture of crack trapping developed in this article.…”

Section: Resultsmentioning

confidence: 99%

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Biologically inspired crack trapping for enhanced adhesion

Glassmaker

Jagota

Hui

et al. 2007

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

244

270

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We present a synthetic adaptation of the fibrillar adhesion surfaces found in nature. The structure consists of protruding fibrils topped by a thin plate and shows an experimentally measured enhancement in adhesion energy of up to a factor of 9 over a flat control. Additionally, this structure solves the robustness problems of previous mimic structures and has preferred contact properties (i.e., a large surface area and a highly compliant structure). We show that this geometry enhances adhesion because of its ability to trap interfacial cracks in highly compliant contact regimes between successive fibril detachments. This results in the requirement that the externally supplied energy release rate for interfacial separation be greater than the intrinsic work of adhesion, in a manner analogous to lattice trapping of cracks in crystalline solids.interface ͉ fracture ͉ fibrillar ͉ lattice trapping ͉ biomechanics T he ability to adhere two surfaces strongly together and then reversibly separate them, repeatedly, is a desirable capability that is rarely achievable using conventional fabrication techniques and materials. Nevertheless, fibrillar surfaces with these properties have evolved in nature on the adhesive surfaces of the feet of many lizards and insects. With such natural surfaces as inspiration, we have developed a fibrillar structure that produces a robust, reusable material with strongly enhanced adhesion compared with a flat control of the same material, with the enhancement resulting only from the modification of surface geometry.The essential feature that our surfaces borrow from biology is the seta, a hair-like bristle having a diameter of 0.5-10 m and terminating in one or more flattened, expanded tips (''spatulas'') at its contacting end. A number of biological studies (1-16) have found that arrays of setae are a common feature on the adhesion surfaces of many lizards and insects. In the biological literature, the shape, dimensions, and composition of setae from various species are described (1-5, 9-16). Also, the mechanical properties and adhesion force of a single gecko seta (7) and even a single spatula (17,18) were the subjects of recent investigations. An important conclusion to emerge from these two studies is that setal arrays use noncovalent surface forces to achieve adhesion, and evidence suggests that geckos rely primarily on van der Waals and capillary forces (8, 18). As a result, the surface architecture is the primary design variable that has been adjusted in biological systems by evolution.Because of the extraordinary adhesion ability of animals that possess setal arrays, several researchers have recently made an effort to mimic the biological setal geometry by using synthetic materials (19)(20)(21)(22)(23)(24)(25)(26). It has been established theoretically that a fibrillar interface can increase both strength and interfacial toughness, compared with a flat control (21, 27-30). However, simple arrays of micropillars (19-21) have not exhibited stronger adhesion than flat control surfaces o...

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Section: Resultsmentioning

confidence: 90%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Biologically inspired crack trapping for enhanced adhesion

Glassmaker

Jagota

Hui

et al. 2007

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

244

270

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“…In the case of adhesive tapes, Kendall has shown that the peeling strength of tapes with patches of different stiffness or thickness can be much higher than the tapes with uniform thickness and stiffness (16). Chaudhury and coworkers have shown that 100-to 200-m patches on poly(dimethylsiloxane) sheets increases the peeling force by a factor of 10-20 in comparison to a unpatterned poly(dimethylsiloxane) sheet (17). We postulate that the mechanism in all of these cases, including the patterned gecko tape, is to stop, deviate, and reinitiate the crack propagation in comparison to materials with uniform properties (also referred to as the Cook-Gordon mechanism) (15).…”

Section: Resultsmentioning

confidence: 99%

Carbon nanotube-based synthetic gecko tapes

Sethi

et al. 2007

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

411

323

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We have developed a synthetic gecko tape by transferring micropatterned carbon nanotube arrays onto flexible polymer tape based on the hierarchical structure found on the foot of a gecko lizard. The gecko tape can support a shear stress (36 N/cm 2 ) nearly four times higher than the gecko foot and sticks to a variety of surfaces, including Teflon. Both the micrometer-size setae (replicated by nanotube bundles) and nanometer-size spatulas (individual nanotubes) are necessary to achieve macroscopic shear adhesion and to translate the weak van der Waals interactions into high shear forces. We have demonstrated for the first time a macroscopic flexible patch that can be used repeatedly with peeling and adhesive properties better than the natural gecko foot. The carbon nanotube-based tape offers an excellent synthetic option as a dry conductive reversible adhesive in microelectronics, robotics, and space applications.adhesives ͉ nanomaterials ͉ hierarchical ͉ robotics F lexible adhesive tapes are indispensable in our daily lives, whether it is to leave a note to a friend or to seal packages. However, we rarely hang heavy objects on a wall using these tapes because the stickiness is time-and rate-dependent. The viscoelastic tapes do not work under vacuum, such as space applications, and where repeated attachment and detachment is required, such as wall-climbing robots. Nature has found an alternate solution to stick to surfaces without using sticky viscoelastic liquids. Natural selection has developed the wallclimbing lizard's foot (Fig. 1A) in a hierarchical structure, consisting of microscopic hairs called setae, which further split into hundreds of smaller structures called spatulas ( Fig. 1B) (1-4). On coming in contact with any surface, the spatulas deform, enabling molecular contact over large areas, thus translating weak van der Waals interactions into enormous attractive forces (4). There have been several theoretical models to elucidate the mechanism of gecko adhesion (5). However, it is not clear why nature has developed this intricate hierarchical structure of micrometer-size setae and nanometer-size spatulas on the gecko foot, instead of covering the whole feet with only setae or spatulas. Many synthetic structures using uniform polymer pillars and in some cases hierarchical structures (6, 7) have been constructed before, although the performance of these structures has not been as good as natural gecko (8, 9). One limitation of these polymer pillars with a high aspect ratio is that they are mechanically weak in comparison to keratin used in the natural foot-hairs.Here we have replicated the multiscale structure of setae and spatulas using microfabricated multiwalled carbon nanotubes and found that not only nanometer-length scales of spatulas (individual carbon nanotubes) but also micrometer-length scales of setae (patterns of carbon nanotubes) are important to support large shear forces. Our results show that a 1-cm 2 area of the carbon nanotube patterns transferred on a flexible tape (referred as a ''gec...

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“…Recent interest in bio-inspired adhesives has motivated many researchers to fabricate microfibril arrays (Liu & Bhushan 2003;Peressadko & Gorb 2004;Chung & Chaudhury 2005;Crosby et al 2005;Glassmaker et al 2005Glassmaker et al , 2007Huber et al 2005;Northen & Turner 2005;Yurdumakan et al 2005;Kim & Sitti 2006;Majidi et al 2006;Aksak et al 2007;Gorb et al 2007;Greiner et al 2007; and to study their contact mechanics and adhesion (Jagota & Bennison 2002;Gao et al 2003Gao et al , 2005Persson & Gorb 2003;Hui et al 2004;Persson et al 2005;Spolenak et al 2005a,b;Tang et al 2005;Bhushan et al 2006;Tian et al 2006;Yao & Gao 2006;Chen & Gao 2007). Most of these studies focus on how the interface between the microfibrils and a smooth, hard substrate separates under a normal load.…”

Section: Introductionmentioning

confidence: 99%

Compliance of a microfibril subjected to shear and normal loads

Liu

Hui

Shen

et al. 2008

J. R. Soc. Interface.

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Many synthetic bio-inspired adhesives consist of an array of microfibrils attached to an elastic backing layer, resulting in a tough and compliant structure. The surface region is usually subjected to large and nonlinear deformations during contact with an indenter, leading to a strongly nonlinear response. In order to understand the compliance of the fibrillar regions, we examine the nonlinear deformation of a single fibril subjected to a combination of shear and normal loads. An exact closed-form solution is obtained using elliptic functions. The prediction of our model compares well with the results of an indentation experiment.

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Roles of discontinuities in bio-inspired adhesive pads

Cited by 185 publications

References 21 publications

Biologically inspired crack trapping for enhanced adhesion

Biologically inspired crack trapping for enhanced adhesion

Carbon nanotube-based synthetic gecko tapes

Compliance of a microfibril subjected to shear and normal loads

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