Mechanics of Bioinspired and Biomimetic Fibrillar Interfaces
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6/12/2007
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est both in studying these structures and in developing and understanding the contact and adhesion of synthetic mimics. Figure 2 shows two examples that are representative of recent fabrication efforts.4–6 This article discusses recent experimental and theoretical work on the contact and adhesion mechanics of such materials. We begin with a review of what is known from biology and the strategies that have been adopted to develop synthetic mimics. The primary mechanical questions concerning the design of natural fibrillar systems and their synthetic mimics are then discussed, and we conclude with a discussion of open problems and our view of the outlook for this subject.
Mechanics of
Bioinspired and Biomimetic Fibrillar Interfaces
A. Jagota, C.-Y. Hui, N.J. Glassmaker, and T. Tang
What Is Known from Studies of Natural Structures As mentioned in the introduction, contacting surfaces in lizards and insects nearly universally consist of hierarchical arrays of fibrils, or setae.2,7–12 The hierarchy comprises branching fibrils commonly tens of microns at their base and terminating in a flattened spatula-like structure. Often, there are three or more levels of fibrillar hierarchy (Figure 1a), although there may be as few as two (Figure 1b). At a coarser length scale, the fibrils are organized in oriented bundles and striations, one important consequence of which is strongly directional adhesion.7,13 While insects often secrete a fluid from their fibrils,2,14 there is considerable evidence that adhesion of lizard fibrils is dry, in that it relies primarily on ubiquitous van der Waals interactions, although recent experiments have shown that adhesion can be enhanced by humidity.15–18 (For
Abstract Materials that are inspired by or are mimics of natural fibrillar surfaces in lizards and insects aim to achieve enhanced interfacial adhesion and contact properties by means of a fibrillar architecture. Studies of the mechanics of deformation and adhesion of such materials help to explain how they work and are aiding the design of their architecture. This article discusses some of the issues addressed by these studies, such as how can a fibrillar interface be made stronger and tougher than a flat control, and how does one enhance its ability to make contact to a variety of substrates?
Introduction Faced with the need for nonspecific adhesion, materials scientists and engineers have developed classes of materials such as pressure-sensitive adhesives,1 which work on a variety of surfaces, and hook–loop fasteners, such as Velcro®, that require a mating architecture. Posed with the same challenge in nature, animals such as lizards and insects have evolved a class of interfaces that share the common motif of hierarchical fibrillar design.2 Figure 1 shows the fibrillar nature of the contact surface in two lizards. Typically, this fibrillar structure is hierarchical, with features that range from millimeter to nanometer in scale. Natural fibrils, termed setae, typically end with a plate-like contact
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