Gecko tape

Micro view of "gecko tape"

Gecko tape (with directional adhesion) is a new material still at the development stage. Directional adhesion refers to the ability of an adhesive material to grip a load in one direction and to release its grip when the direction is reversed.

Description

"Spider-Man test" of gecko tape

Gecko tape, an example of biomimicry, is so called because it is based on the ability of the gecko to adhere to surfaces — regardless of a surface's orientation — due to millions of microscopic hairs, called setae, on the gecko's toes. Due to the principles of electrostatics, the setae of the gecko have a non-zero electrical charge which, when close to a surface, causes the setae and surface to attract.

Although an object normally has an average electrostatic charge of zero, at the microscopic scale of the setae, the charge varies. For example, one side of an individual seta has a slight positive charge while the other has a corresponding negative charge. Furthermore, the point of interaction on the surface also has a slight charge. Where a seta contacts the surface, there is a charge difference leading to an attractive force between the two (the van der Waals force). This force, occurring on a tiny scale between two very close objects, is extremely small, but when multiplied by a large factor, becomes significant. Because the setae on a gecko's toe number in the millions, the combined force is enough that a gecko can hang from a ceiling — of any material — by one foot.^{[citation needed]}

Scientists' effort to replicate the setae, commonly called gecko tape, is still in the early stages of development, but there has been good progress (notably by Andre Geim's group).

Problems

• Self-mating. If the density of the spatulas is too great then self-mating occurs, and scientists have so far been unable to find the correct balance of seta density.^{[citation needed]}

• Self-cleaning. In a gecko the hairy adhesive pads clean themselves of dust so they are reusable. Scientists have been unable to replicate this event, so they have been unable to reuse the tape.^{[citation needed]}

• Surface energy. Different surfaces have different surface energies. For example, a liquid has a higher surface energy than a solid. Within solids the surface energy differs, so a table has less surface energy than Blu-Tack. This is a problem because the correct balance is needed: if there is too little surface energy the tape sticks to nothing, but if there is too much it sticks to the dust and the dirt but not to the surface.^{[citation needed]}

Uses of gecko tape

The predicted uses of gecko tape span from nanosurgery to aerospace. For example, in medicine it could be used as the doctor's "duct tape" to patch up organs and even to deliver medicine directly to the organ needed.^{[citation needed]}

Using a process called soft lithography, scientists have created a polymer that can stretch up to 200% in all directions. This means that the polymer could be placed directly on the heart and mimic its natural rhythm.^{[citation needed]}

In robotics, if gecko tape were fixed to the tracks of robots, they might be able to reach the tops of cliffs or mountains with relative ease. This would make scouting out a landscape easy.^{[citation needed]}

References

• "The Physics of Superheroes", James Kakalios, pp. 174–175
• "Gecko inspires sticky tape", http://news.bbc.co.uk/2/hi/science/nature/2953852.stm
• "Gecko tape will stick you to ceiling", http://www.newscientist.com/article.ns?id=dn3785
• "Will 'Gecko Tape' Let Humans Climb Walls?", http://news.nationalgeographic.com/news/2003/06/0602_030602_geckotape.html