Updated on 10/17/2007
Geckos, polymer nanotubes and studies of natural and synthetic adhesives
The phenomenal ability of geckos to cling to smooth surfaces has captured the attention of biologists and engineers for more than 100 years. Recently much progress has been made in understanding the molecular basis and physical forces underlying these capabilities (1), opening the door to design and manufacture of synthetic adhesive mimics (2-4). As we learn more about the mechanisms underlying adhesion in geckos and other animals (5), it is clear that despite significant morphological convergence in the biological structures responsible for adhesion, considerable variation persists which is likely relevant to the design and production of synthetic adhesives. For example, three taxa of lizards (geckos, anoles and skinks) that independently evolved adhesive toepads all share the fundamental unit involved in adhesion---microscopic hairs called setae (6). However, setae vary significantly in size, shape and form in ways that are often, but not always obviously correlated with function. In cases where we understand how structural variation is directly related to functional consequences, opportunities exist to design mimics with properties tailored to specific applications. By extension, in cases where function seems insensitive to structural variation, there may be opportunities to optimize design and production of synthetic adhesives by choosing materials which are perhaps easier or cheaper to fabricate. Finally, while both engineering and biological analyses have elucidated the mechanics of adhesion at the nano- and micro- scale, maximal advantage of a biomimetic design approach for synthetic adhesives will require better integration of mechanistic understanding from microscopic to the whole organism scale (5,7).
Over the past year I have started to collaborate with a colleague in Polymer Science, Ali Dhinojwala, who together with several colleagues was among the first to produce a synthetic adhesive mimicking both the structure and performance of Gecko adhesive systems (setal arrays on toepads). Most recently, Ali's lab has demonstrated the performance characteristics above the nano and micro scale. The new Integrated Bioscience PhD program at Akron now frames our collaboration in a formal structure encouraging us to add students and other colleagues to a research group exploring the interface of evolutionary biology, materials science and biomimetic design. If you are interested in joining our group, whether your background is in biology, materials science, or some other relevant field, please contact us for information about current opportunities.
Effects of Temperature Variation in Performance of Adhesive Systems
Temperature effects the performance of many biological systems, particularly locomotor systems in ectotherms. Two geckos have been studied and they have shown contrasting results. Tokay geckos (Gekko gecko) show a typical thermal performance profile for clinging ability with an optimum close to typical body temperatures (8), but the clinging ability of Day geckos (Phelsuma dubia) appears to be largely independent of temperature (9). It is currently unclear why there are different effects of temperature on the clinging ability of these two species. Even though G. gecko and P. dubia are fairly closely related (10), it is unclear whether there may be morphological variation in the skeleton-muscular system that controls adhesion and release of setae from substrates (11). Furthermore, there were methodological differences in how clinging performance was measured across the two studies. In either case, further work will be required to determine if differences in temperature dependence of clinging ability between G. gecko and P. dubia is real. We are completing an experiment using live G. gecko and P. dubia to measure the effect of temperature with a single protocol (12). In a closely related project, we will experimentally establish the temperature sensitivity of adhesion strength of synthetic adhesives produced by Dhinojwala’s lab. Although it has not been studied extensively, a comparison between performance of natural and biologically-inspired synthetic materials should provide valuable insights into design constraints and desirable characteristics for the basement layers of synthetic adhesives.
Comparison of clinging ability on hydrophobic and hydrophilic substrates
In progress; look for an update soon
Role of Digital Hyperextension in Self-cleaning
A new project being pursued by a Stephanie Lopez, a masters student who recently started working on geckos.
1 Autumn,K. (2006) How gecko toes stick - The powerful,
fantastic adhesive used by geckos is made of nanoscale hairs that engage tiny
forces, inspiring envy among human imitators. American Scientist 94, 124-132