Stick or Slip: Adhesive Performance of Geckos and Gecko-Inspired Synthetics in Wet Environments
Open Access
- 27 April 2019
- journal article
- research article
- Published by Oxford University Press (OUP) in Integrative and Comparative Biology
- Vol. 59 (1), 214-226
- https://doi.org/10.1093/icb/icz008
Abstract
The gecko adhesive system has inspired hundreds of synthetic mimics principally focused on replicating the strong, reversible, and versatile properties of the natural system. For geckos native to the tropics, versatility includes the need to remain attached to substrates that become wet from high humidity and frequent rain. Paradoxically, van der Waals forces, the principal mechanism responsible for gecko adhesion, reduce to zero when two contacting surfaces separate even slightly by entrapped water layers. A series of laboratory studies show that instead of slipping, geckos maintain and even improve their adhesive performance in many wet conditions (i.e., on wet hydrophobic substrates, on humid substrates held at low temperatures). The mechanism for this is not fully clarified, and likely ranges in scale from the chemical and material properties of the gecko’s contact structures called setae (e.g., setae soften and change surface confirmation when exposed to water), to their locomotor biomechanics and decision-making behavior when encountering water on a substrate in their natural environment (e.g., some geckos tend to run faster and stop more frequently on misted substrates than dry). Current work has also focused on applying results from the natural system to gecko-inspired synthetic adhesives, improving their performance in wet conditions. Gecko-inspired synthetic adhesives have also provided a unique opportunity to test hypotheses about the natural system in semi-natural conditions replicated in the laboratory. Despite many detailed studies focused on the role of water and humidity on gecko and gecko-inspired synthetic adhesion, there remains several outstanding questions: (1) what, if any, role does capillary or capillary-like adhesion play on overall adhesive performance of geckos and gecko-inspired synthetics, (2) how do chemical and material changes at the surface and in the bulk of gecko setae and synthetic fibrils change when exposed to water, and what does this mean for adhesive performance, and (3) how much water do geckos encounter in their native environment, and what is their corresponding behavioral response? This review will detail what we know about gecko adhesion in wet environments, and outline the necessary next steps in biological and synthetic system investigations.Keywords
Funding Information
- The Company of Biologists (EA1696)
- National Science Foundation (1832815)
- Society for Integrative and Comparative Biology
This publication has 108 references indexed in Scilit:
- Immunolocalization of Keratin‐Associated Beta‐Proteins (Beta‐Keratins) in Pad Lamellae of Geckos Suggest that Glycine–Cysteine‐Rich Proteins Contribute to Their Flexibility and AdhesivenessJournal of Experimental Zoology – A (JEZ-A), 2013
- Effects of the relative humidity and water droplet on adhesion of a bio-inspired nano-filmColloids and Surfaces B: Biointerfaces, 2011
- Direct evidence of phospholipids in gecko footprints and spatula–substrate contact interface detected using surface-sensitive spectroscopyJournal of The Royal Society Interface, 2011
- Rate-dependent frictional adhesion in natural and synthetic gecko setaeJournal of The Royal Society Interface, 2009
- Sticky Gecko Feet: The Role of Temperature and HumidityPLOS ONE, 2008
- The adhesion model considering capillarity for gecko attachment systemJournal of The Royal Society Interface, 2007
- Carbon nanotube-based synthetic gecko tapesProceedings of the National Academy of Sciences of the United States of America, 2007
- Ancestrally high elastic modulus of gecko setal β-keratinJournal of The Royal Society Interface, 2007
- Biomimetic mushroom-shaped fibrillar adhesive microstructureJournal of The Royal Society Interface, 2006
- Characterization of the structure and composition of gecko adhesive setaeJournal of The Royal Society Interface, 2005