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 five-toed feet of a gecko are covered with elastic hairs called setae and the ends 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.
Gecko feet
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.
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Adhesion is the tendency of dissimilar particles or surfaces to cling to one another (cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another). The forces that cause adhesion and cohesion can be divided into several types. The intermolecular forces responsible for the function of various kinds of stickers and sticky tape fall into the categories of chemical adhesion, dispersive adhesion, and diffusive adhesion.
Geckos are small, mostly carnivorous lizards that have a wide distribution, found on every continent except Antarctica. Belonging to the infraorder Gekkota, geckos are found in warm climates throughout the world. They range from . Geckos are unique among lizards for their vocalisations, which differ from species to species. Most geckos in the family Gekkonidae use chirping or clicking sounds in their social interactions. Tokay geckos (Gekko gecko) are known for their loud mating calls, and some other species are capable of making hissing noises when alarmed or threatened.
In molecular physics, the van der Waals force is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; they are comparatively weak and therefore more susceptible to disturbance. The van der Waals force quickly vanishes at longer distances between interacting molecules. Named after Dutch physicist Johannes Diderik van der Waals, the van der Waals force plays a fundamental role in fields as diverse as supramolecular chemistry, structural biology, polymer science, nanotechnology, surface science, and condensed matter physics.
The phenomenology of resonant scattering has been known since the earliest experiments upon scattering of atomic beams from surfaces and is a means of obtaining experimental information about the fundamentals of weak adsorption systems in the van der Waals ...
Despite the development of hydrogels with a wide range of mechanical properties, insufficient adhesion between these materials and biological surfaces limits their use in the biomedical applications. Most recent advancements in highly adhesive hydrogel sys ...
Nowadays, bioelectronic devices are evolving from rigid to flexible materials and substrates, among which thermally-drawn-fiber-based bioelectronics represent promising technologies thanks to their inherent flexibility and seamless integration of multi-fun ...