Biological adhesives allow attachment of organisms or animals to surfaces, either temporally or permanently. Microscopic bacteria, fungi, larger marine algae and invertebrates, insects, frogs and even terrestrial vertebrates (i.e. gecko) use specialized adhesive organs and secretions for this purpose. The performance of these adhesives is remarkable, and their diversity suggests the potential for developing adhesion concepts and artificial adhesive materials that are markedly different from those currently available. These bio-inspired adhesives will provide elegant solutions to contemporary engineering and biomedical adhesive requirements, i.e. high adhesion strength and reliability, reversible attachment, or attachment to any surface surfaces including aquatic and fluid environments.

Adhesion to a surface can be mediated by strong chemical bonds or by physical interactions. Covalent and hydrogen bonds are generally used in the animal world for irreversible bonding. In most cases surface reactive species are secreted by the animal and used as a bio-glue to stick to a surface, for example catechol units in DOPA-containing adhesive proteins secreted by mussels.

When reversible adhesion is required, as in adhesive pads used for locomotion, nature utilizes physical interactions enhanced by complex topographical designs. Two main types of adhesive designs are found in the attachment pads of animals: “fibrillar” (in geckos, insects and spiders) and “soft” pads (in crickets and tree and torrent frogs). Both systems allow conformal contact to the substrate independent of the substrate roughness, either using flexible hairs or highly deformable material.

We design and fabricate adhesive polymer materials inspired in these different natural adhesion concepts.

Nature's factory of adhesive	Diagram of “hairy” and “smooth” attachment systems on smooth and structured substrata showing that both systems are able to adapt to the surface profile [4]  SEM pictures of different hairy (A. gecko [5], B. Tarantula Grammostola rosea[6]) and soft (C. great green bush-cricket Tettigonia viridissima[7], D. White’s tree frog Litoria caerulea[8]) pads.

References

1. Bioinspired Topographic Control of Adhesion to Surfaces, A. del Campo*, in “Biomimetic Approaches for Biomaterials Development”, Wiley-VCH, in press
2. Gecko-Inspired Surfaces: A Path to Strong and Reversible Dry Adhesives, L.F. Boesel, C. Greiner, E. Arzt, A. del Campo*, Adv. Mater. 22, 2125–2137 (2010)
3. Design parameters and current fabrication approaches for developing bioinspired dry adhesives, A. del Campo*, E. Arzt, Macromol. Biosci. 7, 118-127 (2007)
4. Costantino Creton and Stanislav Gorb (2007). Sticky Feet: From Animals to Materials. MRS Bulletin, 32 , pp 466-472 doi:10.1557/mrs2007.79
5. Kellar Autumn (2007). Gecko Adhesion: Structure, Function, and Applications. MRS Bulletin, 32 , pp 473-478 doi:10.1557/mrs2007.80
6. Peattie AM, Dirks J-H, Henriques S, Federle W, 2011 Arachnids Secrete a Fluid over Their Adhesive Pads. PLoS ONE 6(5): e20485. doi:10.1371/journal.pone.0020485
7. Journal of Comparative Physiology A: Neuroethology, Sensory, Neural, and Behavioral Physiology. Volume 186, Number 9, 821-831, DOI: 10.1007/s003590000135
8. Ingo Scholz, W. Jon P. Barnes, Joanna M. Smith and Werner Baumgartner. Ultrastructure and physical properties of an adhesive surface, the toe pad epithelium of the tree frog, Litoria caerulea White J Exp Biol 2009 212:155-162. ; doi:10.1242/jeb.019232