Abstract
The adhesive system of geckos has inspired hundreds of synthetic adhesives. While this system has been used relentlessly as a source of inspiration, less work has been done in reverse, where synthetics are used to test questions and hypotheses about the natural system. Here we take such an approach. We tested shear adhesion of a mushroom-tipped synthetic gecko adhesive under conditions that produced perplexing results in the natural adhesive system. Synthetic samples were tested at two temperatures (12 °C and 32 °C) and four different humidity levels (30%, 55%, 70%, and 80% RH). Surprisingly, adhesive performance of the synthetic samples matched that of living geckos, suggesting that uncontrolled parameters in the natural system, such as surface chemistry and material changes, may not be as influential in whole-animal performance as previously thought. There was one difference, however, when comparing natural and synthetic adhesive performance. At 12 °C and 80% RH, adhesion of the synthetic structures was lower than expected based on the natural system’s performance. Our approach highlights a unique opportunity for both biologists and material scientists, where new questions and hypotheses can be fueled by joint comparisons of the natural and synthetic systems, ultimately improving knowledge of both.
Highlights
IntroductionIn 2005, two separate studies found that the normal pull-off force of a single flattened pad (spatula), which forms the tips of the setae, was dependent on humidity, and on capillary adhesion in some form[27,30]
Hydrophilic substrates well during shear sliding[25]
In 2005, two separate studies found that the normal pull-off force of a single flattened pad, which forms the tips of the setae, was dependent on humidity, and on capillary adhesion in some form[27,30]
Summary
In 2005, two separate studies found that the normal pull-off force of a single flattened pad (spatula), which forms the tips of the setae, was dependent on humidity, and on capillary adhesion in some form[27,30] Up until this point, no groups had directly tested the effect of humidity on live animals. Instead of testing the natural system, we take advantage of the controlled parameters of a previously designed gecko-inspired synthetic to probe the basic properties innate to the natural system By using this approach, factors such as modulus change and surface group reorganization can be controlled or eliminated, allowing us to directly compare and contrast synthetic trials with the previous whole animal results. This work tests the performance of synthetic mimics which can adhere at varying temperature and humidity jointly, but is a valuable source of information for future experiments of the natural system, pushing the field forward and in directions we may not have been able to identify without this controlled comparative design
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