© 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Design and Nature, CA Brebbia, L Sucharov & P Pascola (Editors). ISBN 1-85312-901-1 Miniature attachment systems: exploring biological design principles S.N. Gorb Biological Microtribology Group, Division 14 MPI of Developmental Biolop, Tuebingen, Germany. Abstract One of the greatest challenges for engineering science today is miniaturisation. Insects and other arthropods have solved many problems correlated with small size during their evolution. A variety of biomechanical systems of insects, adapted for attachment of parts of the body to each other or attaching the organism to a substrate, are the main topic of the present paper, There are eight fimdamental classes of attachment principles: clamp, spacer, sucker, expansion anchor, hooks, lock or snap, adhesive secretions, and friction. Different combinations of these principles occur in the majority of biological attachment structures. Friction-based probabilistic fasteners provide precise reversible coupling of surfaces with a minimum expenditure of force, Patent databases contain a huge number of ideas dealing with applications of existing fasteners. However, most of these applications use the same types of available hook-like tapes. Biological systems provide a variety of microscale surface patterns, which may serve as a source for Mure prototyping of novel types of releasable fasteners and micro-fasteners. An engineering approach is to copy the surface profile using available technologies. As an initial stage of prototyping diverse surface microsculpture, the low-viscosity wax cast technique is applied to produce surface casts, Since forces in the contact areas of most biological systems have not been previously measured, the fust step in this direction is taken toward identification of the interesting properties of systems. This approach combines the knowledge of biologists and the measuring techniques used in material science. There are three main areas, in which Nature’s solutions of attachment problems may be applied: (1) precise mechanics, (2) gluing and joining technology, and (3) material science of surface-active composite materials. © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Design and Nature, CA Brebbia, L Sucharov & P Pascola (Editors). ISBN 1-85312-901-1 124 DesignandNature 1 Why study biological attachment? Throughout evolution, Nature has constantly been called upon to act as an engineer in solving technical problems. Organisms have evolved an immense variety of shapes and structures. Although often intricate and Ii-agile, they can, nonetheless, deal with extreme mechanical loads. Many tlmctional solutions are based on a variety of ingenious structural solutions, Biologists have collected a huge amount of information about the variety of biomechanical systems adapted for attachment of parts of the body to each other, or attaching the organism to a substrate. Understanding these is of great scientific interest, since we can learn about their use as structural elements and their biological role and function, This knowledge is also highly relevant for technical applications. Information on biological prototypes can be utilised to mimic them for industrial applications. There are three main areas where Nature’s solutions of attachment problems may potentially be applied: (1) precise mechanics, (2) gluing technology, and (3) material science of surface-active composite materials. Possible innovations may also appear at the boundaries of the named areas. Also, knowledge about the properties of biological systems might be useful for pest control, by modifying plant surfaces, In the present paper, we give a short overview of the functional design of attachment devices occurring in insects and how Nature’s design may be used as a basis for biomimetics in various technological areas, 2 Biological attachment devices Biological attachment devices are fi.mctional systems, the purpose of which is either temporary or permanent attachment of an organism to the substrate, to another organism, or temporary interconnection of body parts within an organism. Their design varies enormously and is subject to different functional loads [1], Design and functional principle depend on the biology of the concrete species. The evolutionary background and the habits influence the specific composition of attachment systems in each particular species, In insects and other arthropods, cuticle and its derivatives play a crucial role in the design of the devices, among which eight fimdamental classes of attachment principles have been recognised: (1) hooks, (2) lock or snap, (3) clamp, (4) spacer, (5) sucker, (6) expansion anchor, (7) glue, and (8) friction [2]. Some of them, together with a biological example, are illustrated in Figure 1. Additionally, different combinations of these principles occur in existing attachment structures, Most attachment devices are composed of microscopical structures and driven by muscular force, However, many systems have involved surfaces with particular frictional and adhesive properties. Generally, any movement involving contact between two surfaces or between a surface and a medium deals with the resistance of the surfaces or medium, This resistance is called fi-iction, a phenomenon which has a great influence on the design of biomechanical © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Design and Nature, CA Brebbia, L Sucharov & P Pascola (Editors). ISBN 1-85312-901-1 Design and Nature 125 structures. Living creatures posses specialised surfaces enabling the minimisation of contact forces (anti-friction systems) or their maximisation (friction systems) (Fig. 2). It is interesting that in both cases the resulting task of such a system is to save muscular energy, One always needs friction to generate force for overcoming the drag caused by friction in other parts of the system. Optimisation then becomes the exercise of minimizing friction at one end of the systeu while maximizing it at the other [3], For example, in the case of terrestrial locomotion, for effective propulsive movements, a high ffiction is necessary for contact of the limbs with the substratum and a lower friction – within the joints of the limbs. A Figure 1, Attachment rnicrostructures of insect body based on different principles, Left panels show diagrams explaining principles of attachment in structures shown in right panels, A, Hooks of the wing locking mechanism of the sawfly Cimbex femoratus, B, Lock of the head in the damselfly Pyrrhosoma nymphula. C. Friction-active structures of the head- arresting mechanism of the dragonfly Aeshna mixta, D. Microsuckers of the fust legs in the males of the beetle Dytiscus inarginatus. E, Soft pads of the grasshopper Tettigonia viridissima. F. Hairy pads with anisotropic terminal elements on the legs of the beetle Rhagorzycha fulva, Dark-gray is an animal body; light-gray indicates a substrate. Among various cases of contact pairs in biology, anti-friction systems always have a predefine pair of surfaces, whereas, among friction systems, there are some that deal with predefine surfaces, and others, in which one surface remains unpredictable, The first type of friction system occurs, for example, in wing-locking devices and head-arresting systems and is called probabilistic fasteners [4-6], The second type is mainly represented by insect attachment pads © 2002 WIT Press, Ashurst Lodge, Southampton, SO40 7AA, UK. All rights reserved. Web: www.witpress.com Email [email protected] Paper from: Design and Nature, CA Brebbia, L Sucharov & P Pascola (Editors). ISBN 1-85312-901-1 126 of two alternative designs: hairy and smooth [7], The relationship between surface patterns and/or mechanical properties of materials of contact pairs results in two main working principles of the frictional devices: mechanical interlocking and maximisation of the contact area (Fig. 2). Since biological surfaces are a part of the physical world, most of the friction and adhesion phenomena in biomechanical systems can be explained by mechanical interlocking andlor area of contact between surfaces, independent of the basic physical forces involved in the particular attachment mechanism, This indicates that the geometry of the surface, load forces at which the system operates, and mechanical properties of material will play essential roles in the design of the actual system [8-10], In addition, chemistry of surfaces, the presence and nature of secretory fluids additionally mediate surface forces. Since friction and adhesion are very complex physical phenomena, the biggest challenge in studying them in biological systems is to collect maximum information about gross morphology, ultrastructure, chemistry, and mechanics of surfaces to explain the functional principles of particular attachment systems (Fig, 3). friction anti-friction systems systems / -’% 4 surfaces are one sulfaca is swfaces are pmt%fined mpredictabie pmdofined J/ --m My wnooth w~ mm, Figure 2. Functional significance and working principles of contacting surfaces in biological objects. Living creatures posses specialised surfaces enabling the minimisation of contact forces (anti-friction systems) or their maximisation (friction systems), Among such systems, there are some