Tag Archives: gecko

Change the shape of water with nanotubes

An August 24, 2018 news item on ScienceDaily describes a ‘shapeshifting’ water technique,

First, according to Rice University engineers, get a nanotube hole. Then insert water. If the nanotube is just the right width, the water molecules will align into a square rod.

Rice materials scientist Rouzbeh Shahsavari and his team used molecular models to demonstrate their theory that weak van der Waals forces between the inner surface of the nanotube and the water molecules are strong enough to snap the oxygen and hydrogen atoms into place.

Shahsavari referred to the contents as two-dimensional “ice,” because the molecules freeze regardless of the temperature. He said the research provides valuable insight on ways to leverage atomic interactions between nanotubes and water molecules to fabricate nanochannels and energy-storing nanocapacitors.

An August 24, 2018 Rice University news release (also on EurekAlert and received via email), which originated the news item, delves further,

Shahsavari and his colleagues built molecular models of carbon and boron nitride nanotubes with adjustable widths. They discovered boron nitride is best at constraining the shape of water when the nanotubes are 10.5 angstroms wide. (One angstrom is one hundred-millionth of a centimeter.)

The researchers already knew that hydrogen atoms in tightly confined water take on interesting structural properties. Recent experiments by other labs showed strong evidence for the formation of nanotube ice and prompted the researchers to build density functional theory models to analyze the forces responsible.

Shahsavari’s team modeled water molecules, which are about 3 angstroms wide, inside carbon and boron nitride nanotubes of various chiralities (the angles of their atomic lattices) and between 8 and 12 angstroms in diameter. They discovered that nanotubes in the middle diameters had the most impact on the balance between molecular interactions and van der Waals pressure that prompted the transition from a square water tube to ice.

“If the nanotube is too small and you can only fit one water molecule, you can’t judge much,” Shahsavari said. “If it’s too large, the water keeps its amorphous shape. But at about 8 angstroms, the nanotubes’ van der Waals force [if you’re not familiar with the term, see below the link and citation for my brief explanation] starts to push water molecules into organized square shapes.”

He said the strongest interactions were found in boron nitride nanotubes due to the particular polarization of their atoms.

Shahsavari said nanotube ice could find use in molecular machines or as nanoscale capillaries, or foster ways to deliver a few molecules of water or sequestered drugs to targeted cells, like a nanoscale syringe.

Lead author Farzaneh Shayeganfar, a former visiting scholar at Rice, is an instructor at Shahid Rajaee Teacher Training University in Tehran, Iran. Co-principal investigator Javad Beheshtian is a professor at Amirkabir University, Tehran.

Supercomputer resources were provided with support from the [US] National Institutes of Health and an IBM Shared Rice University Research grant.

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

First Principles Study of Water Nanotubes Captured Inside Carbon/Boron Nitride Nanotubes by Farzaneh Shayeganfar, Javad Beheshtian, and Rouzbeh Shahsavari. Langmuir, DOI: 10.1021/acs.langmuir.8b00856 Publication Date (Web): August 23, 2018

Copyright © 2018 American Chemical Society

This paper is behind a paywall.

For the purposes of the posting, van der Waals force(s) are weak adhesive forces measured at the nanoscale. Humans don’t feel them (we’re too big) but gecko lizards can exploit those forces which is why they are able to hang from the ceiling by a single toe.  There’s a more informed description here in the van der Waals force entry on Wikipedia.

New gecko species in Madagascar with skin specially adapted to tearing

After all these years of writing about geckos and their adhesive properties (they can hang off a wall or ceiling by a single toe), I’ve developed a mild interest in them. From a Feb. 7, 2017 posting by Dirk Steinke for the One species a day blog,

The new species was found in northern Madagascar and its name was build [sic] from the two Greek stems mégas, meaning ‘very large’ and lepís, meaning ‘scale’, and refers to the large size of the scales of this species in comparison to other geckos.

Caption: The new fish-scale gecko, Geckolepis megalepis, has the largest body scales of all geckos. This nocturnal lizard was discovered in the ‘tsingy’ karst formations in northern Madagascar Credit: F. Glaw

There’s more about the new species and the research in a Feb. 7, 2017 PeerJ news release on EurekAlert,

Many lizards can drop their tails when grabbed, but one group of geckos has gone to particularly extreme lengths to escape predation. Fish-scale geckos in the genus Geckolepis have large scales that tear away with ease, leaving them free to escape whilst the predator is left with a mouth full of scales. Scientists have now described a new species (Geckolepis megalepis) that is the master of this art, possessing the largest scales of any gecko.

The skin of fish-scale geckos is specially adapted to tearing. The large scales are attached only by a relatively narrow region that tears with ease, and beneath them they have a pre-formed splitting zone within the skin itself. Together, these features make them especially good at escaping from predators. Although several other geckos are able to lose their skin like this if they are grasped really firmly, Geckolepis are apparently able to do it actively, and at the slightest touch. And while others might take a long time to regenerate their scales, fish-scale geckos can grow them back, scar-free, in a matter of weeks.

This remarkable (if somewhat gruesome) ability has made these geckos a serious challenge to the scientists who want to study them. Early researchers described how it was necessary to catch them with bundles of cotton wool, to avoid them losing almost all of their skin. Today, little has changed, and researchers try to catch them without touching them if possible, by luring them into plastic bags. But once they are caught, the challenges are not over; identifying and describing them is even harder.

“A study a few years ago showed that our understanding of the diversity of fish-scale geckos was totally inadequate,” says Mark D. Scherz, lead author of the new study and PhD student at the Ludwig Maximilian University of Munich and Zoologische Staatssammlung München, “it showed us that there were actually about thirteen highly distinct genetic lineages in this genus, and not just the three or four species we thought existed. One of the divergent lineages they identified was immediately obvious as a new species, because it had such massive scales. But to name it, we had to find additional reliable characteristics that distinguish it from the other species.” A challenging task indeed: one of the main ways reptile species can be told apart is by their scale patterns, but these geckos lose their scales with such ease that the patterns are often lost by the time they reach adulthood. “You have to think a bit outside the box with Geckolepis. They’re a nightmare to identify. So we turned to micro-CT to get at their skeletons and search there for identifying features.” Micro-CT (micro-computed tomography) is essentially a 3D x-ray of an object. This method is allowing morphologists like Scherz to examine the skeletons of animals without having to dissect them, opening up new approaches to quickly study the internal morphology of animals.

By looking at the skeletons of the geckos, the team was able to identify some features of the skull that distinguish their new species from all others. But they also found some surprises; a species named 150 years ago, Geckolepis maculata, was confirmed to be different from the genetic lineage that it had been thought to be. “This is just typical of Geckolepis. You think you have them sorted out, but then you get a result that turns your hypothesis on its head. We still have no idea what Geckolepis maculata really is–we are just getting more and more certain what it’s not.”

The new species, Geckolepis megalepis, which was described by researchers from the US, Germany, and Columbia [sic] in a paper published today in the open access journal PeerJ, is most remarkable because of its huge scales, which are by far the largest of any gecko. The researchers hypothesize that the larger scales tear more easily than smaller scales, because of their greater surface area relative to the attachment area, and larger friction surface. “What’s really remarkable though is that these scales–which are really dense and may even be bony, and must be quite energetically costly to produce–and the skin beneath them tear away with such ease, and can be regenerated quickly and without a scar,” says Scherz. The mechanism for regeneration, which is not well understood, could potentially have applications in human medicine, where regeneration research is already being informed by studies on salamander limbs and lizard tails.

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

Off the scale: a new species of fish-scale gecko (Squamata: Gekkonidae: Geckolepis) with exceptionally large scales by Mark D. Scherz​, Juan D. Daza, Jörn Köhler, Miguel Vences, Frank Glaw. PeerJ 5:e2955 https://doi.org/10.7717/peerj.2955

This paper is open access.

For anyone unfamiliar with ‘gecko research’, scientists are fascinated by their abilities and have been researching them (in a field known as biomimicry or bioinspired engineering or biomimetics) for years with the hope of mimicking those abilities for new applications. You can check out a March 19, 2015 posting or this July 10, 2014 posting for examples or you can search ‘gecko’ on this blog for more examples.

Measuring the van der Waals forces between individual atoms for the first time

A May 13, 2016 news item on Nanowerk heralds the first time measuring the van der Waals forces between individual atoms,

Physicists at the Swiss Nanoscience Institute and the University of Basel have succeeded in measuring the very weak van der Waals forces between individual atoms for the first time. To do this, they fixed individual noble gas atoms within a molecular network and determined the interactions with a single xenon atom that they had positioned at the tip of an atomic force microscope. As expected, the forces varied according to the distance between the two atoms; but, in some cases, the forces were several times larger than theoretically calculated.

A May 13, 2016 University of Basel press release (also on EurekAlert), which originated the news item, provides an explanation of van der Waals forces (the most comprehensive I’ve seen) and technical details about how the research was conducted,

Van der Waals forces act between non-polar atoms and molecules. Although they are very weak in comparison to chemical bonds, they are hugely significant in nature. They play an important role in all processes relating to cohesion, adhesion, friction or condensation and are, for example, essential for a gecko’s climbing skills.

Van der Waals interactions arise due to a temporary redistribution of electrons in the atoms and molecules. This results in the occasional formation of dipoles, which in turn induce a redistribution of electrons in closely neighboring molecules. Due to the formation of dipoles, the two molecules experience a mutual attraction, which is referred to as a van der Waals interaction. This only exists temporarily but is repeatedly re-formed. The individual forces are the weakest binding forces that exist in nature, but they add up to reach magnitudes that we can perceive very clearly on the macroscopic scale – as in the example of the gecko.

Fixed within the nano-beaker

To measure the van der Waals forces, scientists in Basel used a low-temperature atomic force microscope with a single xenon atom on the tip. They then fixed the individual argon, krypton and xenon atoms in a molecular network. This network, which is self-organizing under certain experimental conditions, contains so-called nano-beakers of copper atoms in which the noble gas atoms are held in place like a bird egg. Only with this experimental set-up is it possible to measure the tiny forces between microscope tip and noble gas atom, as a pure metal surface would allow the noble gas atoms to slide around.

Compared with theory

The researchers compared the measured forces with calculated values and displayed them graphically. As expected from the theoretical calculations, the measured forces fell dramatically as the distance between the atoms increased. While there was good agreement between measured and calculated curve shapes for all of the noble gases analyzed, the absolute measured forces were larger than had been expected from calculations according to the standard model. Above all for xenon, the measured forces were larger than the calculated values by a factor of up to two.

The scientists are working on the assumption that, even in the noble gases, charge transfer occurs and therefore weak covalent bonds are occasionally formed, which would explain the higher values.

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

Van der Waals interactions and the limits of isolated atom models at interfaces by Shigeki Kawai, Adam S. Foster, Torbjörn Björkman, Sylwia Nowakowska, Jonas Björk, Filippo Federici Canova, Lutz H. Gade, Thomas A. Jung, & Ernst Meyer. Nature Communications 7, Article number: 11559  doi:10.1038/ncomms11559 Published 13 May 2016

This is an open access paper.

SLIPS (Slippery Liquid-Infused Porous Surfaces) technology repels blood and bacteria from medical devices

Researchers at Harvard University’s Wyss Institute for Biologically Inspired Engineering have developed a coating for medical devices that helps to address some of these devices’ most  troublesome aspects. From an Oct. 12, 2014 news item on ScienceDaily,

From joint replacements to cardiac implants and dialysis machines, medical devices enhance or save lives on a daily basis. However, any device implanted in the body or in contact with flowing blood faces two critical challenges that can threaten the life of the patient the device is meant to help: blood clotting and bacterial infection.

A team of Harvard scientists and engineers may have a solution. They developed a new surface coating for medical devices using materials already approved by the Food and Drug Administration (FDA). The coating repelled blood from more than 20 medically relevant substrates the team tested — made of plastic to glass and metal — and also suppressed biofilm formation in a study reported in Nature Biotechnology. But that’s not all.

The team implanted medical-grade tubing and catheters coated with the material in large blood vessels in pigs, and it prevented blood from clotting for at least eight hours without the use of blood thinners such as heparin. Heparin is notorious for causing potentially lethal side-effects like excessive bleeding but is often a necessary evil in medical treatments where clotting is a risk.

“Devising a way to prevent blood clotting without using anticoagulants is one of the holy grails in medicine,” said Don Ingber, M.D., Ph.D., Founding Director of Harvard’s Wyss Institute for Biologically Inspired Engineering and senior author of the study. Ingber is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School and Boston Children’s Hospital, as well as professor of bioengineering at Harvard School of Engineering and Applied Sciences (SEAS).

An Oct. 12, 2014 Wyss Institute news release (also on EurekAlert), which originated the news item, describes the inspiration for this work,

The idea for the coating evolved from SLIPS, a pioneering surface technology developed by coauthor Joanna Aizenberg, Ph.D., who is a Wyss Institute Core Faculty member and the Amy Smith Berylson Professor of Materials Science at Harvard SEAS. SLIPS stands for Slippery Liquid-Infused Porous Surfaces. Inspired by the slippery surface of the carnivorous pitcher plant, which enables the plant to capture insects, SLIPS repels nearly any material it contacts. The liquid layer on the surface provides a barrier to everything from ice to crude oil and blood.

“Traditional SLIPS uses porous, textured surface substrates to immobilize the liquid layer whereas medical surfaces are mostly flat and smooth – so we further adapted our approach by capitalizing on the natural roughness of chemically modified surfaces of medical devices,” said Aizenberg, who leads the Wyss Institute’s Adaptive Materials platform. “This is yet another incarnation of the highly customizable SLIPS platform that can be designed to create slippery, non-adhesive surfaces on any material.”

The Wyss team developed a super-repellent coating that can be adhered to existing, approved medical devices. In a two-step surface-coating process, they chemically attached a monolayer of perfluorocarbon, which is similar to Teflon. Then they added a layer of liquid perfluorocarbon, which is widely used in medicine for applications such as liquid ventilation for infants with breathing challenges, blood substitution, eye surgery, and more. The team calls the tethered perfluorocarbon plus the liquid layer a Tethered-Liquid Perfluorocarbon surface, or TLP for short.

In addition to working seamlessly when coated on more than 20 different medical surfaces and lasting for more than eight hours to prevent clots in a pig under relatively high blood flow rates without the use of heparin, the TLP coating achieved the following results:

  • TLP-treated medical tubing was stored for more than a year under normal temperature and humidity conditions and still prevented clot formation
  • The TLP surface remained stable under the full range of clinically relevant physiological shear stresses, or rates of blood flow seen in catheters and central lines, all the way up to dialysis machines
  • It repelled the components of blood that cause clotting (fibrin and platelets)
  • When bacteria called Pseudomonas aeruginosa were grown in TLP-coated medical tubing for more than six weeks, less than one in a billion bacteria were able to adhere. Central lines coated with TLP significantly reduce sepsis from Central-Line Mediated Bloodstream Infections (CLABSI). (Sepsis is a life-threatening blood infection caused by bacteria, and a significant risk for patients with implanted medical devices.)

Out of sheer curiosity, the researchers even tested a TLP-coated surface with a gecko – the superstar of sticking whose footpads contain many thousands of hairlike structures with tremendous adhesive strength. The gecko was unable to hold on.

“We were wonderfully surprised by how well the TLP coating worked, particularly in vivo without heparin,” said one of the co-lead authors, Anna Waterhouse, Ph.D., a Wyss Institute Postdoctoral Fellow. “Usually the blood will start to clot within an hour in the extracorporeal circuit, so our experiments really demonstrate the clinical relevance of this new coating.”

While most of the team’s demonstrations were performed on medical devices such as catheters and perfusion tubing using relatively simple setups, they say there is a lot more on the horizon.

“We feel this is just the beginning of how we might test this for use in the clinic,” said co-lead author Daniel Leslie, Ph.D., a Wyss Institute Staff Scientist, who aims to test it on more complex systems such as dialysis machines and ECMO, a machine used in the intensive care unit to help critically ill patients breathe.

I first featured SLIPS technology in a Jan. 15, 2014 post about its possible use for stain-free, self-cleaning clothing. This Wyss Institute video about the latest work featuring the use of  SLIPS technology in medical devices also describes its possible use in pipelines and airplanes,

You can find research paper with this link,

A bioinspired omniphobic surface coating on medical devices prevents thrombosis and biofouling by Daniel C Leslie, Anna Waterhouse, Julia B Berthet, Thomas M Valentin, Alexander L Watters, Abhishek Jain, Philseok Kim, Benjamin D Hatton, Arthur Nedder, Kathryn Donovan, Elana H Super, Caitlin Howell, Christopher P Johnson, Thy L Vu, Dana E Bolgen, Sami Rifai, Anne R Hansen, Michael Aizenberg, Michael Super, Joanna Aizenberg, & Donald E Ingber. Nature Biotechnology (2014) doi:10.1038/nbt.3020 Published online 12 October 2014

This paper is behind a paywall but there is a free preview available via ReadCube Access.

Catch a falling gecko

While discussions of gecko lizards in the ‘nanotechnology world’ are almost always focused on the creature’s adhesive properties, a recent research article in Physical Review E explores the gecko’s ‘loss of grip’. From a July 9, 2014 news item on Nanowerk (Note: A link has been removed),

Geckos and spiders that seem to be able to sit still forever, and walk around upside down have fascinated researchers worldwide for many years. We will soon be able to buy smart new fasteners that hold the same way as the gecko’s foot. But the fact is, sooner or later the grip is lost, no matter how little force is acting on it. Stefan Lindström and Lars Johansson, researchers at the Division of Mechanics, Linköping University, together with Nils Karlsson, recent engineering graduate, have demonstrated this in an article just published in Physical Review E (“Metastable states and activated dynamics in thin-film adhesion to patterned surfaces”).

A June 24, 2014 Linköping University press release (also on EurekAlert but dated July 9, 2014), which originated the news item, describes how this ‘grip loss’ could have implications for graphene production,

…, it’s a phenomenon that can have considerable benefits, for instance in the production of graphene. Graphene consists only of one layer of atom, and which must be easily detached from the substrate.

In his graduation project at the Division of Mechanics, Nils Karlsson studied both the mechanics of the gecko’s leg as well as the adhesion of its foot to the substrate. The gecko’s foot has five toes, all with transverse lamellae. A scanning electron microscope shows that these lamellae consist of a number of small hair-like setae, each with a little film at the end, which resembles a small spatula. These spatulae, roughly 10 nm thick, are what adheres to the substrate.

”At the nano level, conditions are a bit different. The movement of the molecules is negligible in our macroscopic world, but it’s not in the nano world. Nils Karlsson’s graduation project suggested that heat, and consequently the movement of the molecules, has an effect on the adhesion of these spatulae. We wanted to do further analyses, and calculate what actually happens,” explains Stefan Lindström.

They refined the calculations, so they applied to a thin film in contact with an uneven surface (…). So, the film only contacts the uppermost parts of the uneven surface. The researchers also chose to limit the calculations to the type of weak forces that exist between all atoms and molecules – van der Waals forces.

”It’s true, they are small, but they are always there and we know that they are extremely reliant on distance,” says Lars Johansson.

This means that the force is much stronger where the film is very close to a single high point, than when it is quite close to a number of high points. Then, when the film detaches, it does this point by point. This is because both contact surfaces are moving – vibrating. These are tiny movements, but at some stage the movements are in sync, so the surfaces actually lose contact. Then the van der Waals force is so small that the film releases.

”So in reality, we can detach a thin film from the substrate simply by waiting for the right moment. This doesn’t require a great deal of force. The part of the film that remains on the substrate vibrates constantly, and the harder I pull on this part, the faster the film will detach. But how long it takes for the film to detach also depends on the structure of the substrate and the film’s stiffness,” says Stefan Lindström.

In practice this means that even a small force over a long period will cause the film, or for that matter the gecko’s foot, to lose its grip. Which is fine for the gecko, who can scoot off, but maybe not so good for a fastening system. Still – in the right application, this knowledge can be of great industrial benefit.

This is what a gecko’s foot looks like when viewed through a scanning electron microscope,

The pictures of the gecko’s foot is taken by Oskar Geller, Lund University, with a scanning electron microscope.  Linköping University

The pictures of the gecko’s foot is taken by Oskar Geller, Lund University, with a scanning electron microscope. Linköping University

The image looks like a candidate for entry into a nano art show.

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

Metastable states and activated dynamics in thin-film adhesion to patterned surfaces by Stefan B. Lindström, Lars Johansson, and Nils R. Karlsson. DOI 10.1103/PhysRevE.89.062401 Phys. Rev. E 89, 062401 – Published 6 June 2014

This paper is behind a paywall.

Kudos to anyone who recognized the paraphrasing of the song title, ‘Catch a falling star’ in the head for this posting,

Climb like a gecko (in DARPA’s [US Defense Advanced Research Projects Agency] Z-Man program)

I’m not entirely certain why DARPA (US Defense Advanced Research Projects Agency) has now issued a news release (h/t June 5, 2014 news item on Nanowerk) about this achievement (a human climbing like a Gecko) which seems to have first occurred in 2012 but perhaps they want to emphasize that this particular demonstration occurred on a glass wall. In any event, I’m happy to get more news about DARPA’s Z-Man program. From the June 5, 2014 DARPA news release,

DARPA’s Z-Man program has demonstrated the first known human climbing of a glass wall using climbing devices inspired by geckos. The historic ascent involved a 218-pound climber ascending and descending 25 feet of glass, while also carrying an additional 50-pound load in one trial, with no climbing equipment other than a pair of hand-held, gecko-inspired paddles. [emphasis mine] The novel polymer microstructure technology used in those paddles was developed for DARPA by Draper Laboratory of Cambridge, Mass. [Massachusetts]

Historically, gaining the high ground has always been an operational advantage for warfighters, but the climbing instruments on which they’re frequently forced to rely—tools such as ropes and ladders—have not advanced significantly for millennia. Not only can the use of such tools be overt and labor intensive, they also only allow for sequential climbing whereby the first climber often takes on the highest risk.

DARPA created the Z-Man program to overcome these limitations and deliver maximum safety and flexibility for maneuver and rapid response to warfighters operating in tight urban environments. The goal of the program is to develop biologically inspired climbing aids to enable warfighters carrying a full combat load to scale vertical walls constructed from typical building materials.

“The gecko is one of the champion climbers in the Animal Kingdom, so it was natural for DARPA to look to it for inspiration in overcoming some of the maneuver challenges that U.S. forces face in urban environments,” said Dr. Matt Goodman, the DARPA program manager for Z-Man. “Like many of the capabilities that the Department of Defense pursues, we saw with vertical climbing that nature had long since evolved the means to efficiently achieve it. The challenge to our performer team was to understand the biology and physics in play when geckos climb and then reverse-engineer those dynamics into an artificial system for use by humans.”

Geckos can climb on a wide variety of surfaces, including smooth surfaces like glass, with adhesive pressures of 15-30 pounds per square inch for each limb, meaning that a gecko can hang its entire body by one toe. The anatomy of a gecko toe consists of a microscopic hierarchical structure composed of stalk-like setae (100 microns in length, 2 microns in radius). From individual setae, a bundle of hundreds of terminal tips called spatulae (approximately 200 nanometers in diameter at their widest) branch out and contact the climbing surface.

A gecko is able to climb on glass by using physical bond interactions—specifically van der Waals intermolecular forces—between the spatulae and a surface to adhere reversibly, resulting in easy attachment and removal of the gecko’s toes from the surface. The van der Waals mechanism implied that it is the size and shape of the spatulae tips that affect adhesive performance, not specific surface chemistry. This suggested that there were design principles and physical models derived from nature that might enable scientists to fabricate an adhesive inspired by gecko toes.

Humans, of course, have much more weight to carry than a gecko. One of the initial challenges in developing a device to support human climbing was the issue of scaling: a typical Tokay gecko weighs 200 grams, while an average human male weighs 75 kilograms. To enable dynamic climbing like a gecko at this larger scale required that the engineers create climbing paddles capable of balancing sufficient adhesive forces in both the shear (parallel to the vertical surface) and normal (perpendicular to the vertical surface) directions. That feature is necessary for a climber to remain adhered on a surface without falling off while in the act of attaching and detaching the paddles with each movement.

The Draper Laboratory team was also challenged to create novel micro- and nanofabrication technologies to produce the high-aspect-ratio microstructures found in the gecko toe. In the process of achieving that capability, the Z-Man performers transformed the fundamental design and development of reversible adhesives for potential biomedical, industrial, and consumer applications.

The first human climbing demonstration occurred in February 2012 and tests of the technology are ongoing. [emphasis mine]

I’m guessing that glass is difficult to photograph because the image which accompanies the DARPA news release doesn’t highlight the achievement in quite the way one would expect,

During testing, an operator climbed 25 feet vertically on a glass surface using no climbing equipment other than a pair of hand-held, gecko-inspired paddles. The climber wore, but did not require, the use of a safety belay. Image: DARPA

During testing, an operator climbed 25 feet vertically on a glass surface using no climbing equipment other than a pair of hand-held, gecko-inspired paddles. The climber wore, but did not require, the use of a safety belay. Image: DARPA

I last wrote about Z-man in an April 3, 2012 posting highlighting some DARPA-funded work being done at the University of Massachusetts at Amherst while also mentioning work being done in other labs not associated (to my knowledge) with DARPA.

I was not successful in my attempts to find a video highlighting this ‘glass wall’ achievement but I did find this episode of Science Friction, where the host, Rusty Ward, does a very nice job of describing the technology (van der Waals forces, the nanostructures allowing spiders and geckos to climb all sorts of surfaces, etc.) along with some pop culture references (Spider-Man),

This runs for approximately 5 mins. 30 secs., a bit longer than usual for a video embedded here.

One last note, for anyone curious about* the laboratory referenced in the news release, you can find more here at the (Charles Stark) Draper Laboratory Wikipedia entry.

*The word ‘about’ was added June 30, 2022.

Simon Fraser University’s (Canada) gecko-type robots and the European Space Agency

The European Space Agency’s ESTEC technical centre in Noordwijk, the Netherlands has tested Simon Fraser University researchers’ (MENRVA group) robots for potential use in space according to a Jan. 2, 2014 news item on the Canadian Broadcasting Corporation (CBC) News online website,

Canadian engineers, along with researchers from the European Space Agency, have developed lizard-inspired robots that could one day be crawling across the hulls of spacecrafts, doing research and repair work.

The science-fiction scenario is a step closer to reality after engineers from B.C.’s Simon Fraser University created a dry adhesive material that mimics the sticky footpads of gecko lizards.

“This approach is an example of ‘biomimicry,’ taking engineering solutions from the natural world,” said Michael Henrey of Simon Fraser

I have written about an earlier version (so I assume) of this called a Tailless Timing Belt Climbing Platform (TBCP-11) robot in a Nov. 2, 2011 posting, which features a video. As for Abigaille as the robot is currently named, here’s more from the CBC news item,

“Experimental success means deployment in space might one day be possible,” said Laurent Pambaguian of the ESA.

The adhesive was placed on the footpads of six-legged crawling robots, nicknamed Abigaille. Each leg has four degrees of motion, Henrey said, meaning these crawling robots should be able to handle environments that a wheeled robot can’t.

“For example, it can transition from the vertical to horizontal, which might be useful for going around a satellite or overcoming obstacles on the way,” he said.

The Jan. 2, 2014 European Space Agency news release, which originated the news item, describes the gecko’s special abilities and why those abilities could be useful in space,

A gecko’s feet are sticky due to a bunch of little hairs with ends just 100–200 nanometres across – around the scale of individual bacteria. This is sufficiently tiny that atomic interactions between the ends of the hairs and the surface come into play.

“We’ve borrowed techniques from the microelectronics industry to make our own footpad terminators,” he [Michael Henrey of Simon Fraser University] said. “Technical limitations mean these are around 100 times larger than a gecko’s hairs, but they are sufficient to support our robot’s weight.”

Interested in assessing the adhesive’s suitability for space, Michael tested it in ESA’s Electrical Materials and Process Labs, based in the Agency’s ESTEC technical centre in Noordwijk, the Netherlands, with additional support from ESA’s Automation and Robotics Lab.

“The reason we’re interested in dry adhesives is that other adhesive methods wouldn’t suit the space environment,” Michael notes.

“Scotch, duct or pressure-sensitive tape would collect dust, reducing their stickiness over time. They would also give off fumes in vacuum conditions, which is a big no-no because it might affect delicate spacecraft systems.

“Velcro requires a mating surface, and broken hooks could contaminate the robot’s working environment. Magnets can’t stick to composites, for example, and magnetic fields might affect sensitive instruments.”

Here’s what one of these robots looks like,

‘Abigaille’ wall-crawler robot Courtesy: European Space Agency

‘Abigaille’ wall-crawler robot Courtesy: European Space Agency

You can find out more about Simon Fraser University’s (located in Vancouver, Canada) climbing robots here on the Menrva Group webpage. which features both the gecko-type (also called Tank-style robots) and spider-inspired robots.

Self-cleaning gecko feet

I’m back to one of my favourite topics, self’-cleaning products (as I have noted ad nauseam, I long for self-cleaning windows). Scientists at the University of Akron, Ohio, have focussed their attention on the self-cleaning properties of a gecko’s toes. From the June 20, 2012 news release on EurekAlert,

Researchers Shihao Hu, a UA mechanical engineering student, and biologist and recent UA graduate Stephanie Lopez-Chueng of Keiser University in Fort Lauderdale, Fla., and their team discovered that the clue to a dynamic self-cleaning mechanism in gecko setae, or microscopic foot hair, is achieved through the hyperextension of their toes.

“The analysis reveals that geckos have tiny sticky hairs on their toes called setaes, and due to the attaching and detaching mechanism caused by the rolling and peeling motion of their toes as they walk, they release the dirt particles leaving their feet clean,” Hu says. “The dynamic hyperextension effect of its natural toe peeling increases the speed of the cleaning to nearly twice as fast as previously perceived.”

Partners in the study included Hu; Lopez-Chueng; Dr. Peter Niewiarowski, interim director, UA Integrated Bioscience Ph.D. program; and Zhenhai Xia, University of North Texas, Materials Science and Engineering.

The findings, published in the article, “Dynamic Self-Cleaning in Gecko Setae via Digital Hyperextension,” show that a gecko-inspired adhesive can function under conditions where traditional adhesives do not, possibly inspiring new applications in space or water exploration tools or in common items like duct tape or other products that use sticky properties.

My most recent posting about geckos and their bioadhesive qualities is dated April 3, 2012.

I don’t believe I’ve featured a gecko so here’s an image provided by the University of Akron,

Blue-spotted Gecko (A gecko-inspired adhesive can function under conditions where traditional adhesives do not, possibly inspiring new applications, University of Akron)

You can find a full size image and the university of Akron’s June 20, 2012 news release here.

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!