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The natural clinging ability of geckos has inspired hundreds of studies seeking design principles that could be applied to creating synthetic adhesives with the same performance capabilities as the gecko: adhesives that use no glue, are self-cleaning and reusable, and are insensitive to a wide range of surface chemistries and roughness. Important progress has been made, and the basic mechanics of how 'hairy' adhesives work have been faithfully reproduced, advancing theory in surface science and portending diverse practical applications. However, after 15 years, no synthetic mimic can yet perform as well as a gecko and simultaneously meet of all the criteria listed above. Moreover, processes for the production of inexpensive and scalable products are still not clearly in view. Here, we discuss our perspective on some of the gaps in understanding that still remain; these gaps in our knowledge should stimulate us to turn to deeper study of the way in which free-ranging geckos stick to the variety of surfaces found in their natural environments and to a more complete analysis of the materials composing the gecko toe pads. [ABSTRACT FROM AUTHOR]

The gecko adhesive system has been under particular scrutiny forover a decade, as the field has recently attracted attention for its application to bio-inspired design. However, little is known about howthe adhesive system behaves in ecologically relevant conditions. Geckos inhabit a variety of environments, many of which are characterized by high temperature, humidity and rain. The van der Waals-based gecko adhesive system should be particularly challenged by wet substrates because water can disrupt the intimate contact necessary for adhesion. While a few previous studies have focused on the clinging ability of geckos on wet substrates, we tested a dynamic performance characteristic, sprint velocity. To better understand how substrate wettability and running orientation affect locomotor performance of multiple species on wet substrates, we measured average sprint velocity of five species of gecko on substrates that were either hydrophilic or intermediately wetting and oriented either vertically or horizontally. Surprisingly, we found no indication that wet substrates impact average sprint velocity over 1 m, and rather, in some species, sprint velocity was increased on wet substrates rather than reduced. When investigating physical characteristics and behavior that may be associated with running on wet substrates, such as total number of stops, slips andwet toes at thecompletion of a race, we found that there may be habitat-related differences between some species. Our results showthat in general, unlike clinging andwalking, geckos running along wet substrates suffer no significant loss in locomotor performance over short distances. [ABSTRACT FROM AUTHOR]

Despite profound interest in the mechanics and performance of the gecko adhesive system, relatively few studies have focused on performance under conditions that are ecologically relevant to the natural habitats of geckos. Because geckos are likely to encounter surfaces that are wet, we used shear force adhesion measurements to examine the effect of surface water and toe pad wetting on the whole-animal performance of a tropical-dwelling gecko (Gekko gecko). To test the effect of surface wetting, we measured the shear adhesive force of geckos on three substrate conditions: dry glass, glass misted with water droplets and glass fully submerged in water. We also investigated the effect of wetting on the adhesive toe pad by soaking the toe pads prior to testing. Finally, we tested for repeatability of the adhesive system in each wetting condition by measuring shear adhesion after each step a gecko made under treatment conditions. Wetted toe pads had significantly lower shear adhesive force in all treatments (0.86±0.09N) than the control (17.96±3.42N), as did full immersion in water (0.44±0.03N). Treatments with droplets of water distributed across the surface were more variable and did not differ from treatments where the surface was dry (4.72±1.59N misted glass; 9.76±2.81 N dry glass), except after the gecko took multiple steps. These findings suggest that surface water and the wetting of a gecko's adhesive toe pads may have significant consequences for the ecology and behavior of geckos living in tropical environments. [ABSTRACT FROM AUTHOR]