Gecko tape

Synthetic setae emulate the setae found on the toes of a gecko and scientific research in this area is driven towards the development of dry adhesives. Geckos have no difficulty mastering vertical walls and are apparently capable of adhering themselves to just about any surface. The 5-toed feet of a gecko are covered with elastic hairs called setae and the end of these hairs are split into nanoscale structures called spatulae (because of their resemblance to actual spatulas). The sheer abundance and proximity to the surface of these spatulae make it sufficient for van der Waals forces alone to provide the required adhesive strength. Following the discovery of the gecko’s adhesion mechanism in 2002, which is based on van der Waals forces, biomimetic adhesives have become the topic of a major research effort. These developments are poised to yield families of novel adhesive materials with superior properties which are likely to find uses in industries ranging from defense and nanotechnology to healthcare and sport.

Geckos are renowned for their exceptional ability to stick and run on any vertical and inverted surface (excluding Teflon). However gecko toes are not sticky in the usual way like chemical adhesives. Instead, they can detach from the surface quickly and remain quite clean around everyday contaminants even without grooming.

The two front feet of a tokay gecko can withstand 20.1 N of force parallel to the surface with 227 mm² of pad area, a force as much as 40 times the gecko's weight. Scientists have been investigating the secret of this extraordinary adhesion ever since the 19th century, and at least seven possible mechanisms for gecko adhesion have been discussed over the past 175 years. There have been hypotheses of glue, friction, suction, electrostatics, micro-interlocking and intermolecular forces. Sticky secretions were ruled out first early in the study of gecko adhesion since geckos lack glandular tissue on their toes. The friction hypothesis was also dismissed quickly because the friction force only acts in shear which cannot explain the adhesive capabilities of geckos on inverted surfaces. The hypothesis that the toe pads act as suction cups was dispelled in 1934 by experiments carried out in a vacuum in which the gecko's toes remained stuck. Similarly, the electrostatic hypothesis was refuted by an experiment showing that geckos could still adhere even when the build-up of electrostatic charge was impossible (such as on a metal surface in air ionized by a stream of x-rays). The mechanism of microinterlocking which suggested that the curved tips of setae could act as microscale hooks was also challenged by the fact that geckos generate large adhesive forces even on molecularly smooth surfaces.

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Wikipedia