Bio-Inspired Adhesion

....... Examples of adhesive systems are found in the animal kingdom that have properties which man has been challenged to achieve. One of these properties is dynamic or reversible adhesion which is necessary for animals that move and inhabit environments where gravity or fluid flow (wind or water: oceans, rivers) is present. Another property is the ability of various species to achieve adhesion to surfaces in the presence of water. Three classes of adhesion are identified among biological systems: chemical, wet and dry adhesion. Chemical systems are found in marine species that use proteins, polysaccharides and carbohydrates to achieve a variety of chemical bonding. Tree frogs and some insects take advantage of wet adhesion which takes advantage of capillarity and Stefan forces as well as structural toe pad designs that increases liquid drainage and hence frictional contact. Species that employ dry adhesion such as insect and geckos have fibrous arrays which adhere to the surface through van der Waals forces, enabling these species to climb up vertical surfaces. This paper reviews recent research in these three areas of bio-inspired adhesion.