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Functional Surfaces in Biology: Mechanisms and Applications 385

Figure 15.3 Functional diversity of noninnervated cuticular protuberances in insects. (a) Unspecialized polyg-
onal surface on the tarsus of the scarabaeid beetle, Melolontha melolontha, (b) Ommatidia surface in the calliphorid
fly, Calliphora vicina, (c) scales on the dorsal surface of the elytron in the scarabaeid beetle, Hoplia sp., (d) the
surface of a single scale in the scarabaeid beetle, Hoplia sp., (e) wing surface in the bibionid dipteran, Bibio
ferruginatus, (f) pseudotracheae of the labellum in the C. vicina, (g) filter system of the spiracle in the tenebrionid
beetle, Tenebrio molitor, (h) prestomal teeth in the C. vicina, (i) plastron in the nepid bug, Ranatra linearis, and
(j) antiwetting surface in the water-strider, Gerris lacustris. (With permission of Springer Science þ Business
Media B.V.)

contact area between the contacting surfaces and the adhesive substance. Strong adhesion is also
possible between two ideally smooth surfaces. If sufficient contact between the substrate and
adhesive interface is reached, forces will be set up between atoms and molecules of both contacting
materials, and they will adhere. Van der Waals forces are the most common of such forces, together
with the hydrogen bond. Electrostatic forces may be also involved. However, for typical biological
adhesion, their contribution is not significant.
Adhesive organs, which may be used for attachment to substrates as well as being involved in
catching prey, demonstrate a huge diversity among living organisms due to their structural and
chemical properties. Biological adhesion underlies the organization of all living tissues. Cell
contact phenomena have been extensively reviewed in the biomedical and biophysical literature
(Weiss, 1970; Steinberg, 1996; Strange, 1997). The function of attachment appeared very early in
evolution; early unicellular organisms have a variety of cellular adaptations for adhesion. Many
multicellular organisms often bear adhesive organs composed of single cells. In many cases,
however, cells are specialized into glands, which may be composed of several cell types.
Attachment devices are functional systems, the purpose of which is either temporary or
permanent, attachment of an organism to the substrate surface of another organism or temporary
interconnection of body parts within an organism. Their design varies enormously and is subject to