Biological Adhesion for Locomotion on Rough Surfaces: Basic Principles and A Theorist's View

MRS Bulletin 05/2007; 32(06):486 - 490. DOI: 10.1557/mrs2007.82


Surface roughness is the main reason why macroscopic solids usually do not adhere to each other with any measurable strength, and a root-mean-square roughness amplitude of only 1 μm is enough to completely remove the adhesion between normal rubber (with an elastic modulus E ≈ 1 MPa) and a hard, nominally flat substrate. Biological adhesion systems used by insects and geckos for locomotion are built from a relatively stiff material (keratin or chitin–protein composite with E ≈ 1 GPa). Nevertheless, strong adhesion is possible even to very rough substrate surfaces by using noncompact solid structures consisting of fibers (setae) and plates (spatulae). Biological systems use a hierarchical building principle, where the thickness of the fibers or plates decreases as one approaches the outer surface of the attachment pad, to optimize the binding to rough surfaces while simultaneously avoiding elastic instabilities, for example, lateral bundling of fibers.

Full-text preview

Available from:
  • Source
    • "The interaction of adhesives with rough surfaces is of obvious commercial importance and has been the subject of numerous theoretical studies (Fuller and Tabor 1975; Hui et al. 2001; Kendall 2001; Hui et al. 2005; Peressadko et al. 2005; Kim and Bhushan 2007; Persson 2007a). As biological attachment systems have evolved the ability to make contact with diverse substrates of diVerent surface roughness , it is hoped that they can inspire the design of novel adhesives that provide controllable contact to both smooth and rough substrates. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The contact of adhesive structures to rough surfaces has been difficult to investigate as rough surfaces are usually irregular and opaque. Here we use transparent, microstructured surfaces to investigate the performance of tarsal euplantulae in cockroaches (Nauphoeta cinerea). These pads are mainly used for generating pushing forces away from the body. Despite this biological function, shear stress (force per unit area) measurements in immobilized pads showed no significant difference between pushing and pulling on smooth surfaces and on 1-microm high microstructured substrates, where pads made full contact. In contrast, on 4-mum high microstructured substrates, where pads made contact only to the top of the microstructures, shear stress was maximal during a push. This specific direction dependence is explained by the interlocking of the microstructures with nanometre-sized "friction ridges" on the euplantulae. Scanning electron microscopy and atomic force microscopy revealed that these ridges are anisotropic, with steep slopes facing distally and shallow slopes proximally. The absence of a significant direction dependence on smooth and 1-microm high microstructured surfaces suggests the effect of interlocking is masked by the stronger influence of adhesion on friction, which acts equally in both directions. Our findings show that cockroach euplantulae generate friction using both interlocking and adhesion.
    Full-text · Article · Aug 2009 · Journal of Comparative Physiology
  • Source

    Full-text · Article ·
  • [Show abstract] [Hide abstract]
    ABSTRACT: Strong adhesion between solids with rough surfaces is only possible if at least one of the solids is elastically very soft. Some lizards and spiders are able to adhere (dry adhesion) and move on very rough vertical surfaces due to very compliant surface layers on their attachment pads. Flies, bugs, grasshoppers and tree frogs have less compliant pad surface layers, and in these cases adhesion to rough surfaces is only possible because the animals inject a wetting liquid into the pad–substrate contact area, which generates a relative long-range attractive interaction due to the formation of capillary bridges. In this presentation I will discuss some aspects of wet adhesion for tree frogs and give some comments related to tire applications.
    No preview · Article · Aug 2007 · Journal of Physics Condensed Matter
Show more