Tag Archives: Walter Federle

Cambridge University researchers tell us why Spiderman can’t exist while Stanford University proves otherwise

A team of zoology researchers at Cambridge University (UK) find themselves in the unenviable position of having their peer-reviewed study used as a source of unintentional humour. I gather zoologists (Cambridge) and engineers (Stanford) don’t have much opportunity to share information.

A Jan. 18, 2016 news item on ScienceDaily announces the Cambridge research findings,

Latest research reveals why geckos are the largest animals able to scale smooth vertical walls — even larger climbers would require unmanageably large sticky footpads. Scientists estimate that a human would need adhesive pads covering 40% of their body surface in order to walk up a wall like Spiderman, and believe their insights have implications for the feasibility of large-scale, gecko-like adhesives.

A Jan. 18, 2016 Cambridge University press release (also on EurekAlert), which originated the news item, describes the research and the thinking that led to the researchers’ conclusions,

Dr David Labonte and his colleagues in the University of Cambridge’s Department of Zoology found that tiny mites use approximately 200 times less of their total body area for adhesive pads than geckos, nature’s largest adhesion-based climbers. And humans? We’d need about 40% of our total body surface, or roughly 80% of our front, to be covered in sticky footpads if we wanted to do a convincing Spiderman impression.

Once an animal is big enough to need a substantial fraction of its body surface to be covered in sticky footpads, the necessary morphological changes would make the evolution of this trait impractical, suggests Labonte.

“If a human, for example, wanted to walk up a wall the way a gecko does, we’d need impractically large sticky feet – our shoes would need to be a European size 145 or a US size 114,” says Walter Federle, senior author also from Cambridge’s Department of Zoology.

The researchers say that these insights into the size limits of sticky footpads could have profound implications for developing large-scale bio-inspired adhesives, which are currently only effective on very small areas.

“As animals increase in size, the amount of body surface area per volume decreases – an ant has a lot of surface area and very little volume, and a blue whale is mostly volume with not much surface area” explains Labonte.

“This poses a problem for larger climbing species because, when they are bigger and heavier, they need more sticking power to be able to adhere to vertical or inverted surfaces, but they have comparatively less body surface available to cover with sticky footpads. This implies that there is a size limit to sticky footpads as an evolutionary solution to climbing – and that turns out to be about the size of a gecko.”

Larger animals have evolved alternative strategies to help them climb, such as claws and toes to grip with.

The researchers compared the weight and footpad size of 225 climbing animal species including insects, frogs, spiders, lizards and even a mammal.

“We compared animals covering more than seven orders of magnitude in weight, which is roughly the same as comparing a cockroach to the weight of Big Ben, for example,” says Labonte.

These investigations also gave the researchers greater insights into how the size of adhesive footpads is influenced and constrained by the animals’ evolutionary history.

“We were looking at vastly different animals – a spider and a gecko are about as different as a human is to an ant- but if you look at their feet, they have remarkably similar footpads,” says Labonte.

“Adhesive pads of climbing animals are a prime example of convergent evolution – where multiple species have independently, through very different evolutionary histories, arrived at the same solution to a problem. When this happens, it’s a clear sign that it must be a very good solution.”

The researchers believe we can learn from these evolutionary solutions in the development of large-scale manmade adhesives.

“Our study emphasises the importance of scaling for animal adhesion, and scaling is also essential for improving the performance of adhesives over much larger areas. There is a lot of interesting work still to do looking into the strategies that animals have developed in order to maintain the ability to scale smooth walls, which would likely also have very useful applications in the development of large-scale, powerful yet controllable adhesives,” says Labonte.

There is one other possible solution to the problem of how to stick when you’re a large animal, and that’s to make your sticky footpads even stickier.

“We noticed that within closely related species pad size was not increasing fast enough to match body size, probably a result of evolutionary constraints. Yet these animals can still stick to walls,” says Christofer Clemente, a co-author from the University of the Sunshine Coast [Australia].

“Within frogs, we found that they have switched to this second option of making pads stickier rather than bigger. It’s remarkable that we see two different evolutionary solutions to the problem of getting big and sticking to walls,” says Clemente.

“Across all species the problem is solved by evolving relatively bigger pads, but this does not seem possible within closely related species, probably since there is not enough morphological diversity to allow it. Instead, within these closely related groups, pads get stickier. This is a great example of evolutionary constraint and innovation.”

A researcher at Stanford University (US) took strong exception to the Cambridge team’s conclusions , from a Jan. 28, 2016 article by Michael Grothaus for Fast Company (Note: A link has been removed),

It seems the dreams of the web-slinger’s fans were crushed forever—that is until a rival university swooped in and saved the day. A team of engineers working with mechanical engineering graduate student Elliot Hawkes at Stanford University have announced [in 2014] that they’ve invented a device called “gecko gloves” that proves the Cambridge researchers wrong.

Hawkes has created a video outlining the nature of his dispute with Cambridge University and US tv talk show host, Stephen Colbert who featured the Cambridge University research in one of his monologues,

To be fair to Hawkes, he does prove his point. A Nov. 21, 2014 Stanford University report by Bjorn Carey describes Hawke’s ingenious ‘sticky pads,

Each handheld gecko pad is covered with 24 adhesive tiles, and each of these is covered with sawtooth-shape polymer structures each 100 micrometers long (about the width of a human hair).

The pads are connected to special degressive springs, which become less stiff the further they are stretched. This characteristic means that when the springs are pulled upon, they apply an identical force to each adhesive tile and cause the sawtooth-like structures to flatten.

“When the pad first touches the surface, only the tips touch, so it’s not sticky,” said co-author Eric Eason, a graduate student in applied physics. “But when the load is applied, and the wedges turn over and come into contact with the surface, that creates the adhesion force.”

As with actual geckos, the adhesives can be “turned” on and off. Simply release the load tension, and the pad loses its stickiness. “It can attach and detach with very little wasted energy,” Eason said.

The ability of the device to scale up controllable adhesion to support large loads makes it attractive for several applications beyond human climbing, said Mark Cutkosky, the Fletcher Jones Chair in the School of Engineering and senior author on the paper.

“Some of the applications we’re thinking of involve manufacturing robots that lift large glass panels or liquid-crystal displays,” Cutkosky said. “We’re also working on a project with NASA’s Jet Propulsion Laboratory to apply these to the robotic arms of spacecraft that could gently latch on to orbital space debris, such as fuel tanks and solar panels, and move it to an orbital graveyard or pitch it toward Earth to burn up.”

Previous work on synthetic and gecko adhesives showed that adhesive strength decreased as the size increased. In contrast, the engineers have shown that the special springs in their device make it possible to maintain the same adhesive strength at all sizes from a square millimeter to the size of a human hand.

The current version of the device can support about 200 pounds, Hawkes said, but, theoretically, increasing its size by 10 times would allow it to carry almost 2,000 pounds.

Here’s a link to and a citation for the Stanford paper,

Human climbing with efficiently scaled gecko-inspired dry adhesives by Elliot W. Hawkes, Eric V. Eason, David L. Christensen, Mark R. Cutkosky. Jurnal of the Royal Society Interface DOI: 10.1098/rsif.2014.0675 Published 19 November 2014

This paper is open access.

To be fair to the Cambridge researchers, It’s stretching it a bit to say that Hawke’s gecko gloves allow someone to be like Spiderman. That’s a very careful, slow climb achieved in a relatively short period of time. Can the human body remain suspended that way for more than a few minutes? How big do your sticky pads have to be if you’re going to have the same wall-climbing ease of movement and staying power of either a gecko or Spiderman?

Here’s a link to and a citation for the Cambridge paper,

Extreme positive allometry of animal adhesive pads and the size limits of adhesion-based climbing by David Labonte, Christofer J. Clemente, Alex Dittrich, Chi-Yun Kuo, Alfred J. Crosby, Duncan J. Irschick, and Walter Federle. PNAS doi: 10.1073/pnas.1519459113

This paper is behind a paywall but there is an open access preprint version, which may differ from the PNAS version, available,

Extreme positive allometry of animal adhesive pads and the size limits of adhesion-based climbing by David Labonte, Christofer J Clemente, Alex Dittrich, Chi-Yun Kuo, Alfred J Crosby, Duncan J Irschick, Walter Federle. bioRxiv
doi: http://dx.doi.org/10.1101/033845

I hope that if the Cambridge researchers respond, they will be witty rather than huffy. Finally, there’s this gecko image (which I love) from the Cambridge researchers,

 Caption: This image shows a gecko and ant. Credit: Image courtesy of A Hackmann and D Labonte

Caption: This image shows a gecko and ant. Credit: Image courtesy of A Hackmann and D Labonte

Cleaning antennae—ant style

The University of Cambridge (UK) has produced research that could lead to cleaning at the microscale and nanoscale and it’s all due to ants. From a July 28, 2015 news item on Nanowerk (Note: A link has been removed),

For an insect, grooming is a serious business. If the incredibly sensitive hairs on their antennae get too dirty, they are unable to smell food, follow pheromone trails or communicate. So insects spend a significant proportion of their time just keeping themselves clean. Until now, however, no-one has really investigated the mechanics of how they actually go about this.

In a study published in Open Science (“Functional morphology and efficiency of the antenna cleaner in Camponotus rufifemur ants”), Alexander Hackmann and colleagues from the Department of Zoology [University of Cambridge] have undertaken the first biomechanical investigation of how ants use different types of hairs in their cleaning apparatus to clear away dirt from their antennae.

A July 27, 2015 University of Cambridge press release, which originated the news item, expands on the theme,

“Insects have developed ingenious ways of cleaning very small, sensitive structures, so finding out exactly how they work could have fascinating applications for nanotechnology – where contamination of small things, especially electronic devices, is a big problem. Different insects have all kinds of different cleaning devices, but no-one has really looked at their mechanical function in detail before,” explains Hackmann.

Camponotus rufifemur ants possess a specialised cleaning structure on their front legs that is actively used to groom their antennae. A notch and spur covered in different types of hairs form a cleaning device similar in shape to a tiny lobster claw. During a cleaning movement, the antenna is pulled through the device which clears away dirt particles using ‘bristles’, a ‘comb’ and a ‘brush’.

To investigate how the different hairs work, Hackmann painstakingly constructed an experimental mechanism to mimic the ant’s movements and pull antennae through the cleaning structure under a powerful microscope. This allowed him to film the process in extreme close up and to measure the cleaning efficiency of the hairs using fluorescent particles.

What he discovered was that the three clusters of hairs perform a different function in the cleaning process. The dirty antenna surface first comes into contact with the ‘bristles’ (shown in the image in red) which scratch away the largest particles. It is then drawn past the ‘comb’ (shown in the image in blue) which removes smaller particles that get trapped between the comb hairs. Finally, it is drawn through the ‘brush’ (shown in the image in green) which removes the smallest particles.

Scanning electron micrograph of the tarsal notch (Alexander Hackmann). Courtesy: University of Cambridge

Scanning electron micrograph of the tarsal notch (Alexander Hackmann). Courtesy: University of Cambridge

The news release offers more detail about the ‘notch’s’ cleaning properties,

“While the ‘bristles’ and the ‘comb’ scrape off larger particles mechanically, the ‘brush’ seems to attract smaller dirt particles from the antenna by adhesion,” says Hackmann, who works in the laboratory of Dr Walter Federle.

Where the ‘bristles’ and ‘comb’ are rounded and fairly rigid, the ‘brush’ hairs are flat, bendy and covered in ridges – this increases the surface area for contact with the dirt particles, which stick to the hairs. Researchers do not yet know what makes the ‘brush’ hairs sticky – whether it is due to electrostatic forces, sticky secretions, or a combination of factors.

“The arrangement of ‘bristles’, ‘combs’ and ‘brush’ lets the cleaning structure work as a particle filter that can clean different sized dirt particles with a single cleaning stroke,” says Hackmann. “Modern nanofabrication techniques face similar problems with surface contamination, and as a result the fabrication of micron-scale devices requires very expensive cleanroom technology. We hope that understanding the biological system will lead to building bioinspired devices for cleaning on micro and nano scales.”

If you want to see the a video of the ‘cleaning action’, you can check either Nanowerk’s July 28, 2015 news item or the University of Cambridge’s July 27, 2015 press release.

Here’s a link to and citation for the paper,

Functional morphology and efficiency of the antenna cleaner in Camponotus rufifemur ants by Alexander Hackmann, Henry Delacave, Adam Robinson, David Labonte, and Walter Federle. Royal Society Open Science DOI: 10.1098/rsos.150129  Published 22 July 2015

As you may have guessed from the journal’s title, this is an open access paper.

Geckskin and Z-Man

Z-Man or do I mean SpiderMan? They used to make reference to SpiderMan and/or geckos when there was some research breakthrough or other concerning adhesion (specifically, bioadhesion) but these days, it’s all geckos, all the time.

I’m going to start with the first announcement from the research team at the University of Massachusetts at Amherst, from the Feb. 17, 2012 news item on Nanowerk,

For years, biologists have been amazed by the power of gecko feet, which let these 5-ounce lizards produce an adhesive force roughly equivalent to carrying nine pounds up a wall without slipping. Now, a team of polymer scientists and a biologist at the University of Massachusetts Amherst have discovered exactly how the gecko does it, leading them to invent “Geckskin,” a device that can hold 700 pounds on a smooth wall. Doctoral candidate Michael Bartlett in Alfred Crosby’s polymer science and engineering lab at UMass Amherst is the lead author of their article describing the discovery in the current online issue of Advanced Materials (“Looking Beyond Fibrillar Features to Scale Gecko-Like Adhesion”). The group includes biologist Duncan Irschick, a functional morphologist who has studied the gecko’s climbing and clinging abilities for over 20 years. Geckos are equally at home on vertical, slanted, even backward-tilting surfaces.

Here’s a picture illustrating the material’s strength,

A card-sized pad of Geckskin can firmly attach very heavy objects such as this 42-inch television weighing about 40 lbs. (18 kg) to a smooth vertical surface. The key innovation by Bartlett and colleagues was to create a soft pad woven into a stiff fabric that includes a synthetic tendon. Together these features allow the stiff yet flexible pad to “drape” over a surface to maximize contact. Photo courtesy of UMass Amherst

This image is meant as an illustration of what the product could do and not as a demonstration, i.e., the tv is not being held up by ‘geckskin’.

There are other research teams around the world working on ways to imitate the properties of gecko feet or bioadhesion (my Nov. 2, 2011 posting mentions some work on robots with ‘gecko feet’ at Simon Fraser University [Canada] and my March 19, 2012 posting mentions in passing some work being done at the University of Waterloo [Canada] are two recent examples).

The University of Massachusetts team’s innovation (from the Feb. 17, 2012 news item),

The key innovation by Bartlett and colleagues was to create an integrated adhesive with a soft pad woven into a stiff fabric, which allows the pad to “drape” over a surface to maximize contact. Further, as in natural gecko feet, the skin is woven into a synthetic “tendon,” yielding a design that plays a key role in maintaining stiffness and rotational freedom, the researchers explain.

Importantly, the Geckskin’s adhesive pad uses simple everyday materials such as polydimethylsiloxane (PDMS), which holds promise for developing an inexpensive, strong and durable dry adhesive.

The UMass Amherst researchers are continuing to improve their Geckskin design by drawing on lessons from the evolution of gecko feet, which show remarkable variation in anatomy. “Our design for Geckskin shows the true integrative power of evolution for inspiring synthetic design that can ultimately aid humans in many ways,” says Irschick.

The research at the University of Massachusetts is being funded, in part, by DARPA (US Defense Advanced Research Projects Agency) through its Z-man program. From the March 2, 2012 news item on Nanowerk,

“Geckskin” is one output of the Z-Man program. It is a synthetically-fabricated reversible adhesive inspired by the gecko’s ability to climb surfaces of various materials and roughness, including smooth surfaces like glass. Performers on Z-Man designed adhesive pads to mimic the gecko foot over multiple length scales, from the macroscopic foot tendons to the microscopic setae and spatulae, to maximize reversible van der Waals interactions with the surface.

Here’s the reasoning for the Z-Man program, from the March 2, 2012 news item,

The Defense Advanced Research Projects Agency (DARPA)’s “Z-Man program” aims to develop biologically inspired climbing aids to enable soldiers to scale vertical walls constructed from typical building materials, while carrying a full combat load, and without the use of ropes or ladders.

Soldiers operate in all manner of environments, including tight urban terrain. Their safety and effectiveness demand maximum flexibility for maneuvering and responding to circumstances. To overcome obstacles and secure entrance and egress routes, soldiers frequently rely on ropes, ladders and related climbing tools. Such climbing tools cost valuable time to use, have limited application and add to the load warfighters are forced to carry during missions.

The Z-Man program provides more information, as well as, images here, where you will find this image, which is not as pretty as the one with the tv screen but this one is a demonstration,

A proof-of-concept demonstration of a 16-square-inch sheet of Geckskin adhering to a vertical glass wall while supporting a static load of up to 660 pounds. (from the Z-Man Program website)

In the very latest news, the University of Massachusetts team has won international funding for its (and Cambridge University’s) work on bioadhesion. From the University of Massachusetts at Amherst March 28, 2012 [news release],

Duncan Irschick, Biology, and Al Crosby, Polymer Science and Engineering, with Walter Federle of Cambridge University, have been awarded a three-year, $900,000 grant from the Human Frontiers Science Program (HFSP) in Strasbourg, France, to study bioadhesion in geckos and insects.

Theirs was one of only 25 teams from among approximately 800 to apply worldwide. HFSP is a global organization that funds research at the frontiers of the life sciences.

Crosby, Irschick and colleagues received international scientific and media attention over the past several weeks for their discovery reported in the journal Advanced Materials, of how gecko feet and skin produce an adhesive force roughly equivalent to the 5-ounce animal carrying nine pounds up a wall without slipping. This led them to invent “Geckskin,” a device that can hold 700 pounds on a smooth wall. Irschick, a functional morphologist who has studied the gecko’s climbing and clinging abilities for over 20 years, says the lizards are equally at home on vertical, slanted and even backward-tilting surfaces.

Not having heard of the Human Science Frontier Program (HSFP) previously, I was moved to investigate further. From the About Us page,

The Human Frontier Science Program is a program of funding for frontier research in the life sciences. It is implemented by the International Human Frontier Science Program Organization (HFSPO) with its office in Strasbourg.

The members of the HFSPO, the so-called Management Supporting Parties (MSPs) are the contributing countries and the European Union, which contributes on behalf of the non-G7 EU members.

The current MSPs are Australia, Canada, France, Germany, India, Italy, Japan, Republic of Korea, Norway, New Zealand, Switzerland the United Kingdom, the United States of America and the European Union.

I wonder how much impact all the publicity had on the funding decision. In any event, it’s good to find out about a new funding program and I wish anyone who applies the best of luck!