Mimicking Nature, or At Least Trying To
It's fairly well known that the inspiration for Velcro came from cockleburs caught in the hair of George de Mestral's dog, and that Leonardo da Vinci drew on the bird's wing for ideas for his flying machines. It seems that humans have been attempting to copy nature for a very long time, and this impulse continues today, though much of the observation and experimentation is now done at the microscopic and molecular levels. If anything, nature's ingenuity is even more in evidence there. For example, tree frogs have hexagonal cells on their toe pads that are surrounded by mucus-filled channels. The cricket Tettigonia has smooth adhesive pads with a hexagonal pattern of grooves. In each case, the combination of form and material makes for very effective adhesion. Researchers have found that the channels and grooves greatly augment adhesion when combined with the hexagonal pattern of surfaces (Barnes, 2007).

Geckos' feet, too, have gotten a lot of attention in the last few years as a source of insights into how to create an adhesive that is strong, reversible, and reusable. This is a tall order, but geckos obviously have a good solution to the problem because they easily walk, even run, across ceilings. Analysis of their foot pads revealed foot hairs called ‘‘setae’’ that are made of keratin and subdivided into spatulae, creating a large surface area for adhesion (Lee et al., 2007). Humans have devised substances that mimic this ability, but there are two problems. First, the substances weaken with reuse, and second, they don't work well when wet.

To deal with these issues, researchers have looked to another organism noted for its bonding powers, the mussel, which has powerful adhesive proteins in its holdfast. A synthetic polymer with similar properties was coated onto a surface with nano-scale pillars …