Learning from animals
Researchers develop gecko-inspired adhesives
A research team in the University of Alberta's Department of Mechanical Engineering has moved technology to manufacture high-quality dry adhesives that mimic the stickiness of gecko's feet to the threshold of commercial production.
Mechanical engineering professor Dan Sameoto's research team recently published its findings in ACS Applied Materials and Interfaces, a top research journal in the field. The team turned to unorthodox materials and an improvised heat press to prove that the mass production of new adhesives that are strong, reusable and recyclable is possible.
"If you can operate a Panini press, you can manufacture adhesives using this process," said Sameoto.
It's an apt comparison. During a demonstration at his lab in the campus-based National Institute for Nanotechnology, Sameoto places a microscope slide on a hot plate. He then stacks a mold, a single layer of rubbery-looking material (thermoplastic elastomer), and another hard slide on top of one another - like building up ingredients in a sandwich. He then applies pressure from the top so the rubbery elastomer takes on the shape of the mould.
The mould shapes tiny 'hairs' that are inspired by the feet of geckos -- tiny reptiles capable of walking up walls and up-side-down. The bottoms of the lizard's feet are covered with millions of tiny hairs with a triangular shaped tip. Like a gecko's feet, the adhesives Sameoto has been researching for years have tiny 'hairs' that stick to a variety of surfaces and can be used over and over. In recent years, researchers have discovered that by adjusting the hairs so they have an overhanging tip, resembling a mushroom cap, they can increase the material's sticking power.
Applications for dry adhesives reach far beyond traditional adhesives. For example, in the production of microelectronics, tiny chips are handled in high-tech clean rooms by workers who wear 'bunny suits' and use tweezers to handle the chips. But robotics could get the same job done in a vacuumed environment instead of a clean room, using the dry adhesive instead of tweezers. The adhesive could also replace alternative fasteners used in other situations - including work in outer space where suction cups are ineffective and materials may not be magnetic.
Sameoto and graduate student Walid Khaled published findings last November proving they could create directional adhesives. In this study, they examined ways to mass-produce the adhesives. The process has come a long way. In the early days of his studies, Khaled, who travelled from Bangladesh to earn his Master's degree here, produced the adhesives while wearing a face shield and gloves, and had to cure the material under UV light or with chemical methods.
In this new study, the team became the first to use thermoplastic elastomers, a material not commonly used in this area of research. They discovered the material makes production easier because it removes the step of curing it which could take minutes or hours and replaces it with a rapid thermal cycle of less than a minute. It also results in an improved product that leaves no trace residue behind - and is recyclable.
Other research groups developing dry adhesives commonly use curable silicone rubbers or polyurethanes, but when they are peeled off a surface some residue remains on the surface. This could cause problems when using the dry adhesives to move tiny electrical components that need to be kept free of contamination.
"With these thermoplastic elastomers, it's less likely for individual molecules to break off. It's the best way we've found to avoid contamination."
The team is now looking toward testing even more manufacturing techniques, including injection moulding. It is also exploring the possibility of using the rubbery compounds to produce microfluidic chips.
(Source: University of Alberta news release. Article written by Richard Cairney.)