Hierarchical macroscopic fibrillar adhesives: in situ study of buckling and adhesion mechanisms on wavy substrates

Moh

Arzt

2018

Adv Funct Materials

Self Cite

150

Reversible adhesion is the key functionality to grip, place, and release objects nondestructively. Inspired by nature, micropatterned dry adhesives are promising candidates for this purpose and have attracted the attention of research groups worldwide. Their enhanced adhesion compared to nonpatterned surfaces is frequently demonstrated. An important conclusion is that the contact mechanics involved is at least as important as the surface energy and chemistry. In this paper, the roles of the contact geometry and mechanical properties are reviewed. With a focus on applications, the effects of substrate roughness and of temperature variations, and the long-term performance of micropatterned adhesives are discussed. The paper provides a link between the current, detailed understanding of micropatterned adhesives and emerging applications. The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/adfm.201800865.are designated for locomotion over various types of substrates, involving attachment and detachment within milliseconds. [1][2][3][4][5] It is of interest for evolutionary biologists that many foot pads are strikingly similar in morphology: elongated fibrillar structures with aspect ratios ranging from 10 to 80 leading to terminal elements with very different shapes (Figure 1a and Figure 3). [6][7][8][9] For some animals such as the gecko, the adhesive ability of their toe pads can be attributed to van der Waals interactions and, to some extent, to capillary forces. [10][11][12][13][14][15] In the gecko, the fibrillar pads are composed of millions of keratinous hairs (called setae) that branch into even finer terminal elements (spatulae) (Figure 1a). [16,17] Such a hierarchically organized structure results in a soft and compliant surface, which allows easy adaption to roughness at the expense of little strain energy and thus enhances adhesion.More than 1000 reports published in the field of bioinspired dry adhesives over the last two decades reflect a considerable interest in resolving the underlying adhesion mechanisms, e.g., refs. [18][19][20][21]. Application-oriented publications were motivated by a strong interest in creating novel gripper devices and pickand-place systems (Figure 1b), e.g., refs. [18-20] and [22][23][24], climbing robots for terrestrial and extraterrestrial activities, [25][26][27][28][29][30][31][32] new gasket designs in microfluidics, [33,34] or novel solutions for biomedical applications. [35][36][37][38] The present feature article aims to describe the path from fundamental considerations, including a detailed understanding of the relevant contact mechanics, to emerging applications. It is now known that the success of mimicking micropatterned dry adhesives critically depends on the interplay between design parameters, such as dimensions of the structure elements and the terminal tip-shape geometry, and the bulk and surface properties of the materials in contact. How these parameters control the adhesive performance of synthetic...

Section: Principles Of Adhesive Micropatternsmentioning

confidence: 99%

Section: Operating Conditionsmentioning

confidence: 99%

Engineering Micropatterned Dry Adhesives: From Contact Theory to Handling Applications

Moh

Arzt

2018

Adv Funct Materials

Self Cite

150

“…20 Several groups have mimicked such hierarchically assembled structures in artificial designs, 21−24 but many unsolved questions remain: introduction of hierarchy, for example, generally reduces the available contact area in synthetic adhesives and increases the propensity to elastic buckling. 25,26 …”

Section: Introductionmentioning

confidence: 99%

Composite Pillars with a Tunable Interface for Adhesion to Rough Substrates

Fischer

Arzt

ACS Appl. Mater. Interfaces

2016

Self Cite

The benefits of synthetic fibrillar dry adhesives for temporary and reversible attachment to hard objects with smooth surfaces have been successfully demonstrated in previous studies. However, surface roughness induces a dramatic reduction in pull-off stresses and necessarily requires revised design concepts. Toward this aim, we introduce cylindrical two-phase single pillars, which are composed of a mechanically stiff stalk and a soft tip layer. Adhesion to smooth and rough substrates is shown to exceed that of conventional pillar structures. The adhesion characteristics can be tuned by varying the thickness of the soft tip layer, the ratio of the Young’s moduli and the curvature of the interface between the two phases. For rough substrates, adhesion values similar to those obtained on smooth substrates were achieved. Our concept of composite pillars overcomes current practical limitations caused by surface roughness and opens up fields of application where roughness is omnipresent.

“…More recently, studies on the infl uence of technologically relevant rough surfaces on the adhesion of biomimetic adhesives confi rmed that adhesion decreases for rough surfaces when compared to smooth surfaces. [24][25][26][27][28][29][30] Because little is known about the infl uence of micropillar dimensions on dry adhesion of gecko-mimicking structures on rough substrates, the objective of this study is to systematically…”

mentioning

confidence: 99%

Fibrillar Elastomeric Micropatterns Create Tunable Adhesion Even to Rough Surfaces

Barreau

Guimard

et al. 2016

Adv Funct Materials

Self Cite

Biologically inspired, fi brillar dry adhesives continue to attract much attention as they are instrumental for emerging applications and technologies. To date, the adhesion of micropatterned gecko-inspired surfaces has predominantly been tested on stiff, smooth substrates. However, all natural and almost all artifi cial surfaces have roughnesses on one or more different length scales. In the present approach, micropillar-patterned PDMS surfaces with superior adhesion to glass substrates with different roughnesses are designed and analyzed. The results reveal for the fi rst time adhesive and nonadhesive states depending on the micropillar geometry relative to the surface roughness profi le. The data obtained further demonstrate that, in the adhesive regime, fi brillar gecko-inspired adhesive structures can be used with advantage on rough surfaces; this fi nding may open up new applications in the fi elds of robotics, biomedicine, and space exploration.