Literature

Materials scientists are actively researching biological materials, surfaces and functionalities. All forms of life are inspiring innovation and influencing the direction of development. The adhesive mechanisms of climbing animals have also guided materials scientists.

"Climbing animals have many abilities that are the envy of materials scientists. First, they have remarkable powers of adhesion. Even a large gecko can run across a ceiling; a tree frog jumping from branch to branch does not fall so long as a single toe pad makes good contact with the tree; ants can carry more than 100 times their own weight while walking upside-down. Second, the adhesive mechanisms are reversible (geckos can walk at more than 10 steps a second), and detachment is effortless. Third, animal adhesive pads can have self-cleaning properties and thus do not get fouled. Finally, the adhesive pads of geckos only stick when required."

The outcome of some research in this area is provided by Majumder and colleagues in today's Science. "Inspired by the complex subsurface structure of the smooth adhesive pads of tree frogs and insects such as grasshoppers and ants, they show that adhesive force can be increased by up to a factor of 30 by subsurface structures such as air-or fluid-filled pockets."
It is interesting to note the impact made by these biological surfaces on Majumder et al: the feet "show a remarkable ability to attach to almost any surface"; "man-made pressure-sensitive adhesives lack these amazing qualities"; they attribute "the extraordinary ability of naturally occurring adhesives" to "the complex and hierarchal structural morphologies of their attachment pads". Clearly, something significant is going on here.
When mankind produces "future smart adhesives" like those reported, the materials are described as "designed to do particular tasks". They are the product of intelligent agency. However, when superior materials occur in animals (and plants), they are "remarkable mechanisms developed by climbing animals over millions of years of evolution." The problem is that the ability of evolutionary processes to deliver anything that looks like complex specified information, let alone anything inspiring human designers, has yet to be demonstrated. Proofs of evolution based on industrial melanism of peppered moths or changing beak shapes of Galapagos finches are utterly trivial compared with what is being claimed here. We have a situation where evolution is part of the scientific culture, useful only to frame research by showing allegiance to the prevailing philosophy of naturalism. But we need to recognise that this appeal to evolution adds nothing to the research and is irrelevant to the way science is done. We desperately need a more appropriate methodological underpinning for biomimetics. For more on this, go here.

Microfluidic Adhesion Induced by Subsurface Microstructures
Abhijit Majumder, Animangsu Ghatak, and Ashutosh Sharma
Science 318, 12 October 2007: 258-261.

Abstract: Natural adhesives in the feet of different arthropods and vertebrates show strong adhesion as well as excellent reusability. Whereas the hierarchical structures on the surface are known to have a substantial effect on adhesion, the role of subsurface structures such as the network of microchannels has not been studied. Inspired by these bioadhesives, we generated elastomeric layers with embedded air- or oil-filled microchannels. These adhesives showed remarkable enhancement of adhesion (~30 times), which results from the crack-arresting properties of the microchannels, together with the surface stresses caused by the capillary force. The importance of the thickness of the adhesive layer, channel diameter, interchannel spacing, and vertical position within the adhesive has been examined for developing an optimal design of this microfluidic adhesive.

See also:

Barnes, W.J.P., Biomimetic Solutions to Sticky Problems, Science 318, 12 October 2007: 203-204.