Lizard tails and gecko feet inspire industries, students
Friday 24 August 2012
UC Berkeley discoveries about these agile and sticky reptiles have sparked product ideas ranging from rescue robots to sports gear. And they have captured the research imagination of undergraduate and graduate students.
Even Robert Full couldn’t have predicted that his research on the gravity-defying skills of geckos would catch the eye of the sports gear industry. But he’s seen his lab’s discoveries on animal locomotion attract commercial interest in surprising ways.
A professor of integrative biology at UC Berkeley, Full leads a very active research and teaching program focused on the biomechanics and physiology of animal performance. He and his students study the physical and biological underpinnings of animal movement, and test their hypotheses through computer simulations. They have identified a number of strategies that animals have honed to execute super-human feats.
From hypotheses and computer simulations, the lab often moves on to fabricating mini-robot models to nail down the principles they’ve discovered. Their insights have inspired commercial developers to boost the stability and agility of robots and robotic devices. Turning full circle, the performance of the commercially built models has helped the Berkeley scientists refine their understanding of locomotion.
In January of this year, Full’s lab of undergraduate and graduate students collaborated with engineering graduate students and published a paper that made the cover of the prestigious journal Nature. They reported their discovery of how lizards are able to leap toward their target without losing balance. They studied the biomechanics of the lizard’s leap, ran computer simulations of their hypotheses and eventually fabricated a robotic car with a tail called Tailbot to nail down the tail’s key stabilizing features.
They found that lizards swing their tails up to prevent themselves from tumbling forward in the air, and Tailbot helped demonstrate that both robots and lizards need to adjust the angle of their tails to remain upright.
“Inspiration from lizard tails will likely lead to far more agile search-and-rescue robots,” Full said. Many of his lab’s other discoveries have been incorporated into designs by the robotics company Boston Dynamics.
His lab’s scrutiny of creatures, from cockroaches and centipedes to crabs and beetles, has excited undergrad and graduate students in both biology and engineering. Full is certain that challenging students to examine both the biological and engineering components of animal movement creates a dynamic learning environment and at the same time, sets the stage for discovery.
“I believe there is a synergy between research and teaching that is not fully appreciated,” he said. “The best research now is interdisciplinary and collaborative. Students need to gain expertise in one field, but also be able to speak the language of another discipline, so they can have productive exchanges.”
In 2008, he co-founded a new discovery-based teaching program designed specifically to encourage students to integrate their research focus with a second discipline to tackle puzzles about animal locomotion.
In courses at the Center for Interdisciplinary Bio-inspiration in Education and Research, each student runs an experiment to test a hypothesis about some as-yet-unexplained aspect of animal movement. Undergraduates and graduates in the program have access to the newest research equipment, from wind tunnels and water flumes to study natural locomotion, to devices that can measure mechanical properties of muscles and their activation.
Fantastic feet and feats
The gecko-sports gear connection stems from research on geckos’ ability to cling to ceilings and walls, making them look like glued-on ornaments. A smart guess might be that suction, or some sticky substance on its feet, allows a gecko to walk on the ceiling. But that is not what the scientific team discovered.
Full and graduate students Kellar Autum and Tonia Hsieh — both now faculty members — found that more than a million tiny hairs called setae arrayed on gecko feet create an astounding adhesive strength. In fact, Full said, if all the setae were used at the same time, they could lift nearly 30 pounds. The finest of the hair-like setae are less than 10 millionths of an inch wide. They splay out from thicker hairs above, and are themselves split at their tips to form a billion mini-spatula-shaped tips. They constitute what Full calls the “ultimate case of split ends.”
The sheer number of setae is only one of the secrets they uncovered. The research team showed that the spatula-shaped tips provide added surface area on the end of each microscopic stalk. The research also revealed that a gecko’s feet adhere to the surface and are pulled towards the body. When the foot and its setae are pushed away from the body, the foot can easily be pulled off the surface.
Finally, the experiments showed something unexpected about the way the animals move their feet on precipitous surfaces. The geckos essentially curl their toes and each of the millions of individual setae onto the surface they are walking along, and similarly peel them off the surface, much like the action of an inflatable party favor. This allows rapid attachment and detachment in milliseconds.
The extraordinarily small scale and great density of contact between many millions of setae and a climbing surface actually bring molecular forces into play, Full explained, creating an adhesive strength many times greater than the weight of the gecko.
“The setae’s properties require no sticky material,” Full said, “making it an ideal model for a new kind of dry adhesive.”
Collaborating with Full’s lab, UC Berkeley engineering professor Ron Fearing and his students have synthesized gecko setae using a combination of polymers —long-chain molecules commonly used in plastics and other commercially important materials.
Mimicking the gecko’s adhesive skills would have a range of applications, from use in outer space where glue can’t work, to arable, non-sticky bandages that could be applied and removed without adhesive.
The semiconductor industry could use synthetic setae-tipped instruments to move computer wafers without scratching them.
And then there are the sports applications: Nike is investigating such gecko-inspired adhesive materials for new high-friction soccer balls as well as gloves for goalies and baseball batters.
Full’s successes, from basic discovery to the threshold of new commercial products, have gained attention from several quarters. Engineering colleagues at other universities seek collaborations to find practical applications inspired by the biological insights. Meanwhile, the National Science Foundation supports a program Full launched to strengthen multidisciplinary teaching and training.
He seems proudest that his dual-track strategy has helped train a new generation of scientists, steeped in one discipline but fluent enough in another to benefit from new perspectives. If such cross-fertilization can lead to more agile robots and heroic goalie performance, no one can predict what discoveries and products are yet to emerge.
Photo at top of page: A flat-tailed house gecko skydiving in a wind tunnel, showing how geckos are able to glide and maneuver in midair using their large tails. (T. Libby/UC Berkeley photo; copyright PNAS/NAS 2008)