Tag Archives: adhesion

A gripping problem: tree frogs lead the way

Courtesy: University of Glasgow

At least once a year, there must be a frog posting here (ETA: July 31, 2018 at 1640 hours: unusually, this is my second ‘frog’ posting in one week; my July 26, 2018 posting concerns a very desperate frog, Romeo). Prior to Romeo, this March 15, 2018 news item on phys.org tickled my fancy,

Scientists researching how tree frogs climb have discovered that a unique combination of adhesion and grip gives them perfect technique.

The new research, led by the University of Glasgow and published today [March 15, 2018] in the Journal of Experimental Biology, could have implications for areas of science such as robotics, as well as the production of climbing equipment and even tyre manufacture.

A March 15, 2018 University of Glasgow press release, which originated the news item, provides a little more detail,

Researchers found that, using their fluid-filled adhesive toe pads, tree frogs are able to grip to surfaces to climb. When surfaces aren’t smooth enough to allow adhesion, researchers found that the frogs relied on their long limbs to grip around objects.

University of Glasgow scientists Iain Hill and Jon Barnes gave the tree frogs a series of narrow and wide cylinders to climb. The research team found that on the narrow cylinders the frogs used their grip and adhesion pads, allowing them to climb the obstacle at speed. Wider cylinders were too large for the frogs to grip, so they could only climb more slowly using their suction adhesive pads.

When the cylinders were coated in sandpaper, preventing adhesion, the frogs could only climb the narrow ones slowly, using their grip. They were not able to climb the wider cylinders covered in sandpaper as they couldn’t use their grip or adhesion.

Dr Barnes said: “I have worked on tree frog research for many years and I find them fascinating. Work on tree frogs has been of interest to industry and other areas of science in the past, since their climbing abilities can offer us insights into the most efficient way to climb and stick to surfaces.

“Climbing robots, for instance, need ways to stick, they could be based either on gecko climbing or tree frog climbing.  This research demonstrates how a good climbing robot would need to combine gripping and adhesion to climb more efficiently.”

The study, “The biomechanics of tree frogs climbing curved surfaces: a gripping problem” is published in the Journal ofExperimental Biology. The work was funded by the Royal Society, London and by grants from the National Natural Science Foundation of China and the Natural Science Foundation of Jiangsu Province.

Here’s a link to and a citation for the paper (I love the pun in the title),

The biomechanics of tree frogs climbing curved surfaces: a gripping problem by Iain D. C. Hill, Benzheng Dong, W. Jon. P. Barnes, Aihong Ji, Thomas Endlein. Journal of Experimental Biology 2018 : jeb.168179 doi: 10.1242/jeb.168179 Published 19 January 2018

This paper is behind a paywall.

Gecko lets go!

After all these years of writing about geckos and their adhesive properties it seems that geckos sometimes slip or let go, theoretically. (BTW, there’s a Canadian connection’ one of  the researchers is at the University of Calgary in the province of Alberta.) From a July 19, 2017 Cornell University news release (also on EurekAlert),

Geckos climb vertically up trees, walls and even windows, thanks to pads on the digits of their feet that employ a huge number of tiny bristles and hooks.

Scientists have long marveled at the gecko’s adhesive capabilities, which have been described as 100 times more than what is needed to support their body weight or run quickly up a surface.

But a new theoretical study examines for the first time the limits of geckos’ gripping ability in natural contexts. The study, recently published in the Journal of the Royal Society Interface, reports there are circumstances – such as when geckos fear for their lives, leap into the air and are forced to grab on to a leaf below – when they need every bit of that fabled adhesive ability, and sometimes it’s not enough.

“Geckos are notoriously described as having incredible ability to adhere to a surface,” said Karl Niklas, professor of plant evolution at Cornell University and a co-author of the paper. The study’s lead authors, Timothy Higham at the University of California, Riverside, and Anthony Russell at the University of Calgary, Canada, both zoologists, brought Niklas into the project for his expertise on plant biomechanics.

“The paper shows that [adhesive capability] might be exaggerated, because geckos experience falls and a necessity to grip a surface like a leaf that requires a much more tenacious adhesion force; the paper shows that in some cases the adhesive ability can be exceeded,” Niklas said.

In the theoretical study, the researchers developed computer models to understand if there are common-place instances when the geckos’ ability to hold on to surfaces might be challenged, such as when canopy-dwelling geckos are being chased by a predator and are forced to leap from a tree, hoping to land on a leaf below. The researchers incorporated ecological observations, adhesive force measurements, and body size and shape measurements of museum specimens to conduct simulations. They also considered the biomechanics of the leaves, the size of the leaves and the angles on the surface that geckos might land on to determine impact forces. Calculations were also based on worst-case scenarios, where a gecko reaches a maximum speed when it is no longer accelerating, called “terminal settling velocity.”

“Leaves are cantilevered like diving boards and they go through harmonic motion [when struck], so you have to calculate the initial deflection and orientation, and then consider how does that leaf rebound and can the gecko still stay attached,” Niklas said.

The final result showed that in some cases geckos don’t have enough adhesion to save themselves, he added.

Higham and Russell are planning to travel to French Guiana to do empirical adhesive force studies on living geckos in native forests.

The basic research helps people better understand how geckos stick to surfaces, and has the potential for future applications that mimic such biological mechanisms.

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

Leaping lizards landing on leaves: escape-induced jumps in the rainforest canopy challenge the adhesive limits of geckos by Timothy E. Higham, Anthony P. Russell, Karl J. Niklas. Journal of the Royal Society Interface June 2017 Volume 14, issue 131 DOI: 10.1098/rsif.2017.0156 Published 28 June 2017

I think the authors had some fun with that title. In any event, the paper is behind a paywall.

Ocean-inspired coatings for organic electronics

An Oct. 19, 2016 news item on phys.org describes the advantages a new coating offers and the specific source of inspiration,

In a development beneficial for both industry and environment, UC Santa Barbara [University of California at Santa Barbara] researchers have created a high-quality coating for organic electronics that promises to decrease processing time as well as energy requirements.

“It’s faster, and it’s nontoxic,” said Kollbe Ahn, a research faculty member at UCSB’s Marine Science Institute and corresponding author of a paper published in Nano Letters.

In the manufacture of polymer (also known as “organic”) electronics—the technology behind flexible displays and solar cells—the material used to direct and move current is of supreme importance. Since defects reduce efficiency and functionality, special attention must be paid to quality, even down to the molecular level.

Often that can mean long processing times, or relatively inefficient processes. It can also mean the use of toxic substances. Alternatively, manufacturers can choose to speed up the process, which could cost energy or quality.

Fortunately, as it turns out, efficiency, performance and sustainability don’t always have to be traded against each other in the manufacture of these electronics. Looking no further than the campus beach, the UCSB researchers have found inspiration in the mollusks that live there. Mussels, which have perfected the art of clinging to virtually any surface in the intertidal zone, serve as the model for a molecularly smooth, self-assembled monolayer for high-mobility polymer field-effect transistors—in essence, a surface coating that can be used in the manufacture and processing of the conductive polymer that maintains its efficiency.

An Oct. 18, 2016 UCSB news release by Sonia Fernandez, which originated the news item, provides greater technical detail,

More specifically, according to Ahn, it was the mussel’s adhesion mechanism that stirred the researchers’ interest. “We’re inspired by the proteins at the interface between the plaque and substrate,” he said.

Before mussels attach themselves to the surfaces of rocks, pilings or other structures found in the inhospitable intertidal zone, they secrete proteins through the ventral grove of their feet, in an incremental fashion. In a step that enhances bonding performance, a thin priming layer of protein molecules is first generated as a bridge between the substrate and other adhesive proteins in the plaques that tip the byssus threads of their feet to overcome the barrier of water and other impurities.

That type of zwitterionic molecule — with both positive and negative charges — inspired by the mussel’s native proteins (polyampholytes), can self-assemble and form a sub-nano thin layer in water at ambient temperature in a few seconds. The defect-free monolayer provides a platform for conductive polymers in the appropriate direction on various dielectric surfaces.

Current methods to treat silicon surfaces (the most common dielectric surface), for the production of organic field-effect transistors, requires a batch processing method that is relatively impractical, said Ahn. Although heat can hasten this step, it involves the use of energy and increases the risk of defects.

With this bio-inspired coating mechanism, a continuous roll-to-roll dip coating method of producing organic electronic devices is possible, according to the researchers. It also avoids the use of toxic chemicals and their disposal, by replacing them with water.

“The environmental significance of this work is that these new bio-inspired primers allow for nanofabrication on silicone dioxide surfaces in the absence of organic solvents, high reaction temperatures and toxic reagents,” said co-author Roscoe Lindstadt, a graduate student researcher in UCSB chemistry professor Bruce Lipshutz’s lab. “In order for practitioners to switch to newer, more environmentally benign protocols, they need to be competitive with existing ones, and thankfully device performance is improved by using this ‘greener’ method.”

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

Molecularly Smooth Self-Assembled Monolayer for High-Mobility Organic Field-Effect Transistors by Saurabh Das, Byoung Hoon Lee, Roscoe T. H. Linstadt, Keila Cunha, Youli Li, Yair Kaufman, Zachary A. Levine, Bruce H. Lipshutz, Roberto D. Lins, Joan-Emma Shea, Alan J. Heeger, and B. Kollbe Ahn. Nano Lett., 2016, 16 (10), pp 6709–6715
DOI: 10.1021/acs.nanolett.6b03860 Publication Date (Web): September 27, 2016

Copyright © 2016 American Chemical Society

This paper is behind a paywall but the scientists have made an illustration available,

An artist's concept of a zwitterionic molecule of the type secreted by mussels to prime surfaces for adhesion Photo Credit: Peter Allen

An artist’s concept of a zwitterionic molecule of the type secreted by mussels to prime surfaces for adhesion Photo Credit: Peter Allen

Gluing a broken heart back together

The Jan. 8, 2014 news item on ScienceDaily doesn’t identify which creature(s) may have inspired the heart glue developed by researchers from Brigham and Women’s Hospital (BWH), Boston Children’s Hospital, and Massachusetts Institute of Technology (MIT),

When a child is born with a heart defect such as a hole in the heart, the highly invasive therapies are challenging due to an inability to quickly and safely secure devices inside the heart. Sutures take too much time to stitch and can cause stress on fragile heart tissue, and currently available clinical adhesives are either too toxic or tend to lose their sticking power in the presence of blood or under dynamic conditions, such as in a beating heart.

“About 40,000 babies are born with congenital heart defects in the United States annually, and those that require treatment are plagued with multiple surgeries to deliver or replace non-degradable implants that do not grow with young patients,” says Jeffrey Karp, PhD, Division of Biomedical Engineering, BWH Department of Medicine, co-senior study author of a new study that may improve how surgeons treat congenital heart defects.

In the preclinical study, researchers from Boston Children’s Hospital, BWH and Massachusetts Institute of Technology (MIT) developed a bio-inspired adhesive that could rapidly attach biodegradable patches inside a beating heart — in the exact place where congenital holes in the heart occur, such as with ventricular heart defects.

The Jan. 8, 2014 BWH news release on EurekAlert, which originated the news item, discusses the use of adhesives for repair in the body and some of the specifics of this particular application,

Recognizing that many creatures in nature have secretions that are viscous and repel water, enabling them to attach under wet and dynamic conditions, the researchers developed a material with these properties that also is biodegradable, elastic and biocompatible. According to the study authors, the degradable patches secured with the glue remained attached even at increased heart rates and blood pressure.

“This adhesive platform addresses all of the drawbacks of previous systems in that it works in the presence of blood and moving structures,” says Pedro del Nido, MD, Chief of Cardiac Surgery, Boston Children’s Hospital, co-senior study author. “It should provide the physician with a completely new, much simpler technology and a new paradigm for tissue reconstruction to improve the quality of life of patients following surgical procedures.”

Unlike current surgical adhesives, this new adhesive maintains very strong sticking power when in the presence of blood, and even in active environments.

“This study demonstrated that the adhesive was strong enough to hold tissue and patches onto the heart equivalent to suturing,” says the study’s co-first author Nora Lang, MD, Department of Cardiac Surgery, Boston Children’s Hospital. “Also, the adhesive patch is biodegradable and biocompatible, so nothing foreign or toxic stays in the bodies of these patients.”

Importantly, its adhesive abilities are activated with ultraviolent (UV) light, providing an on-demand, anti-bleeding seal within five seconds of UV light application when applied to high-pressure large blood vessels and cardiac wall defects.

“When we attached patches coated with our adhesive to the walls of a beating heart, the patches remained despite the high pressures of blood flowing through the heart and blood vessels,” says Maria N. Pereira, PhD, Division of Biomedical Engineering, BWH Department of Medicine, co-first study author.

The researchers note that their waterproof, light-activated adhesive will be useful in reducing the invasiveness of surgical procedures, as well as operating times, in addition to improving heart surgery outcomes.

As to which creature(s) may have inspired the glue, perhaps this offers a hint,

The adhesive technology (and other related platforms) has been licensed to a start-up company, Gecko Biomedical, based in Paris. [emphasis mine] The company has raised 8 million Euros in their recently announced Series A financing round and expects to bring the adhesive to the market within two to three years.

The last time geckos and adhesives were mentioned here was in a Jan. 2, 2014 posting titled: Simon Fraser University’s (Canada) gecko-type robots and the European Space Agency.

Getting back to the heart glue, here’s an image illustrating the researchers’ work,

Caption: The waterproof, light-activated glue developed by researchers at Brigham and Women's Hospital, Boston Children's Hospital and Massachusetts Institute of Technology can successfully secure biodegradable patches to seal holes in a beating heart. Credit: Karp Laboratory

Caption: The waterproof, light-activated glue developed by researchers at Brigham and Women’s Hospital, Boston Children’s Hospital and Massachusetts Institute of Technology can successfully secure biodegradable patches to seal holes in a beating heart.
Credit: Karp Laboratory

For the interested, here’s a link to and a citation for the paper,

A Blood-Resistant Surgical Glue for Minimally Invasive Repair of Vessels and Heart Defects by Nora Lang, Maria J. Pereira, Yuhan Lee, Ingeborg Friehs, Nikolay V. Vasilyev, Eric N. Feins, Klemens Ablasser, Eoin D. O’Cearbhaill, Chenjie Xu, Assunta Fabozzo, Robert Padera, Steve Wasserman, Franz Freudenthal, Lino S. Ferreira, Robert Langer, Jeffrey M. Karp, and Pedro J. del Nido. Sci Transl Med 8 January 2014: Vol. 6, Issue 218, p. 218ra6 Sci. Transl. Med. DOI: 10.1126/scitranslmed.3006557

This paper is behind a paywall.

Stickybots at Stanford University

I’ve been intrigued by ‘gecko technology’ or ‘spiderman technology’ since I first started investigating nanotechnology about four years ago.  This is the first time I’ve seen theory put into practice. From the news item on Nanowerk,

Mark Cutkosky, the lead designer of the Stickybot, a professor of mechanical engineering and co-director of the Center for Design Research [Stanford University], has been collaborating with scientists around the nation for the last five years to build climbing robots.

After designing a robot that could conquer rough vertical surfaces such as brick walls and concrete, Cutkosky moved on to smooth surfaces such as glass and metal. He turned to the gecko for ideas.

“Unless you use suction cups, which are kind of slow and inefficient, the other solution out there is to use dry adhesion, which is the technique the gecko uses,” Cutkosky said.

Here’s a video of Stanford’s Stickybot in  action (from the Stanford University News website),

As Cutkosky goes on to explain in the news item,

The interaction between the molecules of gecko toe hair and the wall is a molecular attraction called van der Waals force. A gecko can hang and support its whole weight on one toe by placing it on the glass and then pulling it back. It only sticks when you pull in one direction – their toes are a kind of one-way adhesive, Cutkosky said.

“Other adhesives are sort of like walking around with chewing gum on your feet: You have to press it into the surface and then you have to work to pull it off. But with directional adhesion, it’s almost like you can sort of hook and unhook yourself from the surface,” Cutkosky said.

After the breakthrough insight that direction matters, Cutkosky and his team began asking how to build artificial materials for robots that create the same effect. They came up with a rubber-like material with tiny polymer hairs made from a micro-scale mold.

The designers attach a layer of adhesive cut to the shape of Stickybot’s four feet, which are about the size of a child’s hand. As it steadily moves up the wall, the robot peels and sticks its feet to the surface with ease, resembling a mechanical lizard.

The newest versions of the adhesive, developed in 2009, have a two-layer system, similar to the gecko’s lamellae and setae. The “hairs” are even smaller than the ones on the first version – about 20 micrometers wide, which is five times thinner than a human hair. These versions support higher loads and allow Stickybot to climb surfaces such as wood paneling, painted metal and glass.

The material is strong and reusable, and leaves behind no residue or damage. Robots that scale vertical walls could be useful for accessing dangerous or hard to reach places.

The research team’s paper, Effect of fibril shape on adhesive properties, was published online Aug. 2, 2010 in Applied Physics Letter.