Using a technique that University of Alberta mechanical engineering professor Dan Sameoto compares to a panini sandwich press, pellets of thermoplastic elastomers are squashed onto a substrate to form an innovative adhesive that mimics the sticky feet of one of nature’s champion climbers, the gecko lizard.
Sameoto has been investigating this so-called “gecko glue” for the past six years, starting with his post-doctoral research. In contrast to agents that bond surfaces by means of soft, tacky interfaces, this type of adhesive copies the gecko’s foot pads, which are covered with fine hairs to create a design that holds fast when the hairs get as close as a nanometre to an opposing surface. The real gecko foot hairs are scaled down to the nanometre level, with fibres so fine that significant bonding pressure can be achieved by taking advantage of the otherwise weak van der Waals force between molecules.
Pellets of thermoplastic elastomers, the basis of “gecko glue.” Photo credit: Dan Sameoto.
At the heart of making gecko glue is the production of flexible moulds to form these filaments, as well as eliminating contaminants from the source material that would compromise the quality of these structures. The initial laboratory work has taken advantage of micro fabrication tools that were originally developed to etch fine channels in computer chips, but this approach is expensive and time consuming.
According to Sameoto, if gecko glue is ever to become a commercial product, it will have to be manufactured in a different way. In a paper published in ACS Applied Materials & Interfaces, he and colleague Walid Bin Khaled describe the much simpler “panini press” strategy, which could be embraced by industry for high-volume production. “What we’ve shown in our recent work is not only are these new classes of thermoplastic elastomers attractive from a low-contamination perspective, but we can also manufacture them in a time frame on the order of seconds, as opposed to hours or days,” he says. “We can now use industrial-scale fabrication technologies, like extrusion, embossing, or injection moulding. We can produce these things with the same industrial technologies that are being used to produce inexpensive plastic parts.”
To help test this, the researchers received funding through the Natural Sciences and Engineering Research Council’s Research Tools and Instrument Grant Program to purchase equipment similar to that used in factories where plastic is moulded for various purposes. “The same kind of technology that can make Lego and disposable utensils conceivably can make these micro-adhesives,” says Sameoto.
It will be a long journey to commercialization, however. “It is extraordinarily difficult to convince a company to put in the time and effort to put this into production. There is an extra amount of effort that goes into taking a laboratory-scale, few square centimetres and turn it into hundreds of square metres of this stuff every day.”