1. Biomedical Engineering Department,
2. Material Science and Engineering Department,
3. Institute for BioNanotechnology in Medicine, Northwestern University, Evanston, Illinois 60208, USA
4. Nerites Corporation, 525 Science Drive, Suite 215, Madison, Wisconsin 53711, USA

Correspondence to: Phillip B. Messersmith^1,2,3 Correspondence and requests for materials should be addressed to P.B.M. (Email: philm@northwestern.edu).

Abstract

The adhesive strategy of the gecko relies on foot pads composed of specialized keratinous foot-hairs called setae, which are subdivided into terminal spatulae of approximately 200 nm (ref. 1). Contact between the gecko foot and an opposing surface generates adhesive forces that are sufficient to allow the gecko to cling onto vertical and even inverted surfaces. Although strong, the adhesion is temporary, permitting rapid detachment and reattachment of the gecko foot during locomotion. Researchers have attempted to capture these properties of gecko adhesive in synthetic mimics with nanoscale surface features reminiscent of setae^{2, 3, 4, 5, 6, 7}; however, maintenance of adhesive performance over many cycles has been elusive^{2, 8}, and gecko adhesion is greatly diminished upon full immersion in water^{9, 10}. Here we report a hybrid biologically inspired adhesive consisting of an array of nanofabricated polymer pillars coated with a thin layer of a synthetic polymer that mimics the wet adhesive proteins found in mussel holdfasts. Wet adhesion of the nanostructured polymer pillar arrays increased nearly 15-fold when coated with mussel-mimetic polymer. The system maintains its adhesive performance for over a thousand contact cycles in both dry and wet environments. This hybrid adhesive, which combines the salient design elements of both gecko and mussel adhesives, should be useful for reversible attachment to a variety of surfaces in any environment.

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