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  • Research Progress on "Biomimetic Mechanics of Geckos and Insects
    Author:   | Date:2007-01-11   | Click Rate:    | 【Close
         An interesting observation is that, while geckos and some insects have adopted hairy tissues, some other insects seem to have smooth tissues. For example, the attachment pad of cicada exhibits a smooth outer membranous layer covering an anisotropic microstructure made of highly elongated foams. The attachment pad of grasshopper shows a smooth membrane covering arrays of cross-linked rod-like fibers that are branches of thicker principal rods located deeper in the cuticle and oriented at some angle to the cuticle surface. These biological adhesion systems show two kinds of microstructure designs, i.e. the hairy and the smooth attachments pads. The most important feature of these adhesion systems is the strong elastic anisotropy in the overall property of the tissues. Why most biological adhesive tissues are anisotropic is a very significant problem to be studied. How do the animals and insects realize reversible adhesion for locomotion?

        Dr. S. Chen, LNM, Institute of Mechanics of CAS, and his collaborator, Prof. H. Gao, Brown University of USA, have developed an anisotropic contact model of reversible adhesion, in which a rigid cylinder is in contact with a transversely isotropic elastic half space whose symmetry axis is inclined at an angle. An external force is applied to pull the cylinder in an arbitrary direction. The contact region is assumed to be perfectly bonded.

        The analysis indicates that the adhesion force or strength exhibits a maximum value when pulling along the stiff direction and a minimum value when pulling along the soft direction of the transversely isotropic substrate material. For strongly anisotropic materials, the adhesion strength could vary more than an order of magnitude as the pulling angle changes. A switch between attachment and detachment can thus be accomplished simply by shifting the pulling angle. In contrast, the adhesion strength of an isotropic material is found to be relatively insensitive to the pulling direction. Such orientation-dependent adhesion provides a foundation for understanding reversible adhesion mechanisms in biological systems where adhesion must be not only robust but also easily reversible upon animal movement. This strategy can be summarized as “stiff-adhere and soft-release”.

        The results are expected to provide theoretical guidance for the designs of reversible adhesion devices and micro-robots that can move on arbitrary surfaces.

        This study will be published in Journal of the Mechanics and Physics of Solids. "Bio-inspired mechanics of reversible adhesion: Orientation-dependent adhesion strength for non-slipping adhesive contact with transversely isotropic elastic materials. In Press, Available online 20 December 2006."

        The work is supported by the NSFC (10672165) and Max Planck Visiting Scientist Fellowship.
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