• Cidade, Maria Teresa
• Passos Coelho, José Luís
• Bordado, J. C.
• Duarte, António Paulo David Silva

Abstract

<p>Over the years, the conception of new materials has been inspired by several processes developed by Nature over millions of years, that presenting remarkable properties. For example Velcro, a kind of fabric made of nylon and mainly used as a fastener for clothing, bags and shoes, was developed from the interlocking mechanism of burdock seeds. Similarly, self-cleaning materials have been developed based on "Lotus effect" which describes the way in which water drops roll off the super hydrophobic leaves of lotus plants, taking dirt particles away with them. A concise review of adhesives inspired by biological systems is presented, with a detailed comparison of the different components of the adhesion, as well as the potential final applications. The protein-based underwater adhesives produced by aquatic organisms, such as blue mussels, sea stars, acorn barnacles, sea urchins, freshwater caddis fly larvas and sandcastle worms (phragmatopoma californica) will also be reviewed, along with high-performance adhesives for aqueous milieu, based on the glue secreted by sandcastle worms and used for hold neighbouring particles which then assemble into hollow macroscopic housing colonies to provide protection from predators. The development of surgical adhesives inspired by marine mussels for different applications (prosthetic mesh fixation, islet transplantation, etc.) will also be addressed. Several approaches for creating a responsive fibrillar adhesive system inspired by the gecko, using different materials, have been shown to possess the capacity to generate strong adhesions in dry conditions.Based on that, several researchers have synthesized gecko foot-hairs as dry adhesives for wall-climbing robots. The ability of leaf beetles to climb smooth and rough surfaces using an array of micron-sized adhesive hairs (setae), of varying morphology, which help male beetles achieve strong adhesion to the elytra of females during copulation, can be used as inspiration to develop new adhesives. A successfully developed, spider-inspired hydrophobic hair structure for forming air shield underwater suggests promising applications in underwater protection and adhesives integration. The study of the pads of different insect species leads to the conclusion that smooth pads are specialized for smoother substrates, while rough pads generate stronger forces on a broader range of surfaces and have also inspired scientists in a number of ways. Tree frogs secrete a wetting liquid into the pad substrate contact area, which generates a relative long-range attractive interaction due to the formation of capillary bridges. This system is relevant for some technological applications, for instance, tires for passenger cars have drainage channels to speed up the removal of water from the tyre-road footprint area during wet road conditions. Noteworthy is the fact that it is also possible to successfully develop a biomimetic structure that adheres equally well in wet and dry conditions, for example by combining the microstructure of gecko pads with a thin layer of synthetic polymer that mimics the protein glue of mussels. The bibliographic search now presented individualizes the scope of actuation and prevalence of different adhesion mechanisms showing how they can be used for the development of new adhesion systems.</p>

Topics

• impedance spectroscopy
• microstructure
• morphology
• surface
• polymer
• forming