Space-Age Bonding

Based on his doctoral research into polymer MEMS processing, Simon Fraser University PhD graduate Dan Sameoto has developed a new method of creating microscopic structures from plastic. The first application of this new process is the development of a “dry adhesive” that mimics the stickiness of gecko feet.

Sameoto’s dry adhesive was created using a plastic polymer mold to form microscopic “mushrooms” (about a micron in size) on the surface of a silicone rubber sheet. Rather than using a very soft glue-like material to provide tackiness (as in traditional tapes), such biomimetic adhesives use nano-sized fibres that stick in low-pressure or vacuum environments using van der Waals force, the attractive or repulsive force between molecules effective over very small distances.

“Scotch tape can only be used a couple times and then it’s pretty much gummed up,” he says, “whereas these fibres, when you take them off, dirt particles can easily fall off the edge of the fibres.”

The former SFU engineering science student spent his post-graduate career researching microelectromechanical systems (MEMS), which are microscopic machines that reside on silicon microchips. The field of polymer micromachining, however, is relatively new. Sameoto and his former supervisor, Ash Parameswaran, are investigating new techniques to test and optimize new polymer materials and process variations—which is how the gecko-foot adhesive came about.

Sameoto says there’s already out-of-this-world interest in the innovation. MENRVA, an SFU-based research group focusing on the design and development of different climbing systems, is currently collaborating with the European Space Agency to develop a spider-like robot destined to explore Mars. The dry adhesive would allow the robot “grip” virtually any surface.

“This stuff works in a vacuum and under most atmospheric conditions,” Sameoto says of the ESA project, which is currently in the development stages. There is one problem, he admits; the adhesive works a little too well.

“We can get the feet to stick to a wall, but the motors are having difficulty taking them off. So what we’re trying to do right now is improve the directionality of the adhesive; we need to make sure it will stick on with a minimal pre-force, but it also needs to be easily released when the motor loads it a certain way.”

At this stage of development, they have successfully manufactured dry adhesives in sizes up to 10 centimeters in diameter (a limitation of the silicon wafer substrates they use). Their fabrication reliability, however, has improved dramatically and allowed them to tailor the size and shape of the mushroom-shaped tips. In the future, plastic MEMS will be cheap enough, Sameoto says, that single-use disposable plastic MEMS could conceivably be used in any number of medical and other biological applications, as well as replacements for everyday sticky needs, such as Post-It notes and Scotch tape.
http://fas.sfu.ca/