Category Archives: biomimcry

Like a starfish shell, facetless crystals

Made by accident, these facetless crystals could prove useful in applications for cells, medications, and more according to researchers at the University of Michigan in an Oct. 20, 2014 news item on Nanowerk,

In a design that mimics a hard-to-duplicate texture of starfish shells, University of Michigan engineers have made rounded crystals that have no facets.

“We call them nanolobes. They look like little hot air balloons that are rising from the surface,” said Olga Shalev, a doctoral student in materials science and engineering who worked on the project.

There is a video with the researcher, Olga Shalev, describing the nanolobes in more detail,

An Oct. 17, 2014 University of Michigan news release (also on EurekAlert*), which originated the news item, offers text for those who prefer to read about the science rather than receive it by video,

Both the nanolobes’ shape and the way they’re made have promising applications, the researchers say. The geometry could potentially be useful to guide light in advanced LEDs, solar cells and nonreflective surfaces. A layer might help a material repel water or dirt. And the process used to manufacture them – organic vapor jet printing – might lend itself to 3D-printing medications that absorb better into the body and make personalized dosing possible.

The nanoscale shapes are made out of boron subphthalocyanine chloride, a material often used in organic solar cells. It’s in a family of small molecular compounds that tend to make either flat films or faceted crystals with sharp edges, says Max Shtein, an associate professor of materials science and engineering, macromolecular science and engineering, chemical engineering, and art and design.

“In my years of working with these kinds of materials, I’ve never seen shapes that looked like these. They’re reminiscent of what you get from biological processes,” Shtein said. “Nature can sometimes produce crystals that are smooth, but engineers haven’t been able to do it reliably.”

Echinoderm sea creatures such as brittle stars have ordered rounded structures on their bodies that work as lenses to gather light into their rudimentary eyes. But in a lab, crystals composed of the same minerals tend either to be faceted with flat faces and sharp angles, or smooth, but lacking molecular order.

The U-M researchers made the curved crystals by accident several years ago. They’ve since traced their steps and figured out how to do it on purpose.

In 2010, Shaurjo Biswas, then a doctoral student at U-M, was making solar cells with the organic vapor jet printer. He was recalibrating the machine after switching between materials. Part of the recalibration process involves taking a close look at the fresh layers of material, of films, printed on a plate. Biswas X-rayed several films of different thicknesses to observe the crystal structure. He noticed that the boron subphthalocyanine chloride, which typically does not form ordered shapes, started to do so once the film got thicker than 600 nanometers. He made some thicker films to see what would happen.

“At first, we wondered if our apparatus was functioning properly,” Shtein said.

At 800 nanometers thick, the repeating nanolobe pattern emerged every time.

For a long while, the blobs were lab curiosities. Researchers were focused on other things. Then doctoral student Shalev got involved. She was fascinated by the structures and wanted to understand the reason for the phenomenon. She repeated the experiments in a modified apparatus that gave more control over the conditions to vary them systematically. She collaborated with physics professor Roy Clarke to gain a better understanding of the crystallization, and mechanical engineering professor Wei Lu to simulate the evolution of the surface.. She’s first author of a paper on the findings published in the current edition of Nature Communications.

“As far as we know, no other technology can do this,” Shalev said.

The organic vapor jet printing process the researchers use is a technique Shtein helped to develop when he was in graduate school. He describes it as spray painting, but with a gas rather than with a liquid. It’s cheaper and easier to do for certain applications than competing approaches that involve stencils or can only be done in a vacuum, Shtein says. He’s especially hopeful about the prospects for this technique to advance emerging 3D-printed pharmaceutical concepts.

For example, Shtein and Shalev believe this method offers a precise way to control the size and shape of the medicine particles, for easier absorption into the body. It could also allow drugs to be attached directly to other materials and it doesn’t require solvents that might introduce impurities.

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

Growth and modelling of spherical crystalline morphologies of molecular materials by O. Shalev, S. Biswas, Y. Yang, T. Eddir, W. Lu, R. Clarke,  & M. Shtein. Nature Communications 5, Article number: 5204 doi:10.1038/ncomms6204 Published 16 October 2014

This paper is behind a paywall.

* EurekAlert link added on Oct. 20, 2014 at 1035 hours PDT.

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.

Sharklet’s sharkskin-like material

It’s one of my favourite technologies but there hasn’t been much talk about Sharklet for the last few years. My Feb. 10, 2011 posting about it had this,

They used sharkskin as an example for making a ‘smarter’ material. Scientists have observed that nanoscale structures on a shark’s skin have antibacterial properties. This is especially important when we have a growing problem with bacteria that are antibiotic resistant. David Pogue’s (the program host) interviewed scientists at Sharklet and highlighted their work producing a plastic with nanostructures similar to those found on sharkskin for use in hospitals, restaurants, etc.  I found this on the Sharklet website (from a rotating graphic on the home page),

The World Health Organization calls antibiotic resistance a leading threat to human health.

Sharkjet provides a non-toxic approach to bacterial control and doesn’t create resistance.

The reason that the material does not create resistance is that it doesn’t kill the bacteria (antibiotics kill most bacteria but cannot kill all of them with the consequence that only the resistant survive and reproduce). Excerpted from Sharklet’s technology page,

While the Sharklet pattern holds great promise to improve the way humans co-exist with microorganisms, the pattern was developed far outside of a laboratory. In fact, Sharklet was discovered via a seemingly unrelated problem: how to keep algae from coating the hulls of submarines and ships. In 2002, Dr. Anthony Brennan, a materials science and engineering professor at the University of Florida, was visiting the U.S. naval base at Pearl Harbor in Oahu as part of Navy-sponsored research. The U.S. Office of Naval Research solicited Dr. Brennan to find new antifouling strategies to reduce use of toxic antifouling paints and trim costs associated with dry dock and drag.

The most recent news from Sharklet comes in a Sept. 16, 2014 news release on EurekAlert which refines the definition for Sharklet and provides research about the latest research on this material,

Transmission of bacterial infections, including MRSA and MSSA could be curbed by coating hospital surfaces with microscopic bumps that mimic the scaly surface of shark skin, according to research published in the open access journal Antimicrobial Resistance and Infection Control.

The study modelled how well different materials prevented the spread of human disease bacteria through touching, sneezes or spillages. The micropattern, named Sharklet™, is an arrangement of ridges formulated to resemble shark skin. The study showed that Sharklet harboured 94% less MRSA bacteria than a smooth surface, and fared better than copper, a leading antimicrobial material. The bacteria were less able to attach to Sharklet’s imperceptibly textured surface, suggesting it could reduce the spread of superbugs in hospital settings.

The surfaces in hospitals and healthcare settings are often rife with bacteria and patients are vulnerable to bacterial infection. Scientists are investigating the ability of different materials to prevent the spread of bacteria. Copper alloys are a popular option, as they are toxic to bacterial cells, interfering with their cellular processes and killing them. The Sharklet micropattern works differently – the size and composition of its microscopic features prevent bacteria from attaching to it. It mimics the unique qualities of shark skin, which, unlike other underwater surfaces, inhibits bacteria, because it is covered with a natural micropattern of tooth-like structures, called denticles.

Dr Ethan Mann, a research scientist at Sharklet Technologies, the manufacturer of the micropattern, says: “The Sharklet texture is designed to be manufactured directly into the surfaces of plastic products that surround patients in hospital, including environmental surfaces as well as medical devices. Sharklet does not introduce new materials or coatings – it simply alters the shape and texture of existing materials to create surface properties that are unfavorable for bacterial contamination.”

The researchers from Sharklet Technologies compared how well two types of infection-causing bacteria, methicillin-resistant or susceptible Staphylococcus aureus (MRSA and MSSA), fared at contaminating three surfaces – the Sharklet micropattern, a copper alloy, and a smooth control surface. They created experimental procedures to mimic common ways bacteria infect surfaces. Sneezing was mimicked by using a paint sprayer to spread the bacterial solution on 10 samples of each surface. To mimic infected patients touching the surfaces, velveteen cloth was put in contact with bacteria for 10s, and then placed on another set of each test surface for 10s. A third set of each surface was immersed in bacterial solution for an hour, then rinsed and dried, to mimic spills.

Surfaces were sampled for remaining contaminations either immediately following exposure to MSSA and MRSA or 90 minutes after being exposed. The Sharklet micropattern reduced transmission of MSSA by 97% compared to the smooth control, while copper was no better than the control. The micropattern also harboured 94% less MRSA bacteria than the control surface, while the copper had 80% less.

Dr Mann says: “Shark skin itself is not an antimicrobial surface, rather it seems highly adapted to resist attachment of living organisms such as algae and barnacles. Shark skin has a specific roughness and certain properties that deter marine organisms from attaching to the skin surface. We have learned much from nature in building this material texture for the future.”

Here’s an illustration the researchers have provided,

Caption: This is an image of the Sharklet micropattern, which mimics the denticles of shark skin. Credit: Mann et al.

Caption: This is an image of the Sharklet micropattern, which mimics the denticles of shark skin.
Credit: Mann et al.

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

Surface micropattern limits bacterial contamination by Ethan E Mann, Dipankar Manna, Michael R Mettetal, Rhea M May, Elisa M Dannemiller, Kenneth K Chung, Anthony B Brennan, and Shravanthi T Reddy. Antimicrobial Resistance and Infection Control 2014, 3:28  doi:10.1186/2047-2994-3-28

This is an open access paper.

Mothbots (cyborg moths)

Apparently the big picture could involve search and rescue applications, meanwhile, the smaller picture shows attempts to create a cyborg moth (mothbot). From an Aug. 20, 2014 news item on ScienceDaily,

North Carolina State University [US] researchers have developed methods for electronically manipulating the flight muscles of moths and for monitoring the electrical signals moths use to control those muscles. The work opens the door to the development of remotely-controlled moths, or “biobots,” for use in emergency response.

“In the big picture, we want to know whether we can control the movement of moths for use in applications such as search and rescue operations,” says Dr. Alper Bozkurt, an assistant professor of electrical and computer engineering at NC State and co-author of a paper on the work. “The idea would be to attach sensors to moths in order to create a flexible, aerial sensor network that can identify survivors or public health hazards in the wake of a disaster.”

An Aug. 20, 2014 North Carolina State University news release (also on EurekAlert), which originated the news item,

The paper presents a technique Bozkurt developed for attaching electrodes to a moth during its pupal stage, when the caterpillar is in a cocoon undergoing metamorphosis into its winged adult stage. This aspect of the work was done in conjunction with Dr. Amit Lal of Cornell University.

But the new findings in the paper involve methods developed by Bozkurt’s research team for improving our understanding of precisely how a moth coordinates its muscles during flight.

By attaching electrodes to the muscle groups responsible for a moth’s flight, Bozkurt’s team is able to monitor electromyographic signals – the electric signals the moth uses during flight to tell those muscles what to do.

The moth is connected to a wireless platform that collects the electromyographic data as the moth moves its wings. To give the moth freedom to turn left and right, the entire platform levitates, suspended in mid-air by electromagnets. A short video describing the work is available at http://www.youtube.com/watch?v=jR325RHPK8o.

“By watching how the moth uses its wings to steer while in flight, and matching those movements with their corresponding electromyographic signals, we’re getting a much better understanding of how moths maneuver through the air,” Bozkurt says.

“We’re optimistic that this information will help us develop technologies to remotely control the movements of moths in flight,” Bozkurt says. “That’s essential to the overarching goal of creating biobots that can be part of a cyberphysical sensor network.”

But Bozkurt stresses that there’s a lot of work yet to be done to make moth biobots a viable tool.

“We now have a platform for collecting data about flight coordination,” Bozkurt says. “Next steps include developing an automated system to explore and fine-tune parameters for controlling moth flight, further miniaturizing the technology, and testing the technology in free-flying moths.”

Here’s an image illustrating the researchers’ work,

Caption: The moth is connected to a wireless platform that collects the electromyographic data as the moth moves its wings. To give the moth freedom to turn left and right, the entire platform levitates, suspended in mid-air by electromagnets. Credit: Alper Bozkurt

Caption: The moth is connected to a wireless platform that collects the electromyographic data as the moth moves its wings. To give the moth freedom to turn left and right, the entire platform levitates, suspended in mid-air by electromagnets.
Credit: Alper Bozkurt

I was expecting to find this research had been funded by the US military but that doesn’t seem to be the case according to the university news release,

… The research was supported by the National Science Foundation, under grant CNS-1239243. The researchers also used transmitters and receivers developed by Triangle Biosystems International and thank them for their contribution to the work.

For the curious, here’s a link to and a citation for the text and the full video,

Early Metamorphic Insertion Technology for Insect Flight Behavior Monitoring by Alexander Verderber, Michael McKnight, and Alper Bozkurt. J. Vis. Exp. (89), e50901, doi:10.3791/50901 (2014)

This material is behind a paywall.

White beetles and complex photonic nanostructures

At least one species of white beetles which have excited scientists with their complex nanostructures are native to Southeast Asia according to an Aug. 15, 2014 news item on Nanowerk,

The physical properties of the ultra-white scales on certain species of beetle could be used to make whiter paper, plastics and paints, while using far less material than is used in current manufacturing methods.

The Cyphochilus beetle, which is native to South-East Asia, is whiter than paper, thanks to ultra-thin scales which cover its body. A new investigation of the optical properties of these scales has shown that they are able to scatter light more efficiently than any other biological tissue known, which is how they are able to achieve such a bright whiteness.

An Aug. 15, 2014 University of Cambridge press release (also on EurekAlert), which originated the news item, describes the properties needed to create the optical conditions necessary for the colour white to be seen,

Animals produce colours for several purposes, from camouflage to communication, to mating and thermoregulation. Bright colours are usually produced using pigments, which absorb certain wavelengths of light and reflect others, which our eyes then perceive as colour.

To appear as white, however, a tissue needs to reflect all wavelengths of light with the same efficiency. The ultra-white Cyphochilus and L. Stigma beetles produce this colouration by exploiting the geometry of a dense complex network of chitin – a molecule similar in structure to cellulose, which is found throughout nature, including in the shells of molluscs, the exoskeletons of insects and the cell walls of fungi. The chitin filaments are just a few billionths of a metre thick, and on their own are not particularly good at reflecting light.

The research, a collaboration between the University of Cambridge and the European Laboratory for non-Linear Spectroscopy in Italy has shown that the beetles have optimised their internal structure in order to produce maximum white with minimum material, like a painter who needs to whiten a wall with a very small quantity of paint. This efficiency is particularly important for insects that fly, as it makes them lighter.

Here’s what the Cyphochilus beetle looks like,

Cyphochilus beetle Credit: Lorenzo Cortese and Silvia Vignolini

Cyphochilus beetle Credit: Lorenzo Cortese and Silvia Vignolini Courtesy University of Cambridge

The press release goes on to describe the beetle’s optical properties in greater detail,

Over millions of years of evolution the beetles have developed a compressed network of chitin filaments. This network is directionally-dependent, or anisotropic, which allows high intensities of reflected light for all colours at the same time, resulting in a very intense white with very little material.

“Current technology is not able to produce a coating as white as these beetles can in such a thin layer,” said Dr Silvia Vignolini of the University’s Cavendish Laboratory, who led the research. “In order to survive, these beetles need to optimise their optical response but this comes with the strong constraint of using as little material as possible in order to save energy and to keep the scales light enough in order to fly. Curiously, these beetles succeed in this task using chitin, which has a relatively low refractive index.”

The secret lies in the beetles’ nanostructures,

Exactly how this could be possible remained unclear up to now. The researchers studied how light propagates in the white scales, quantitatively measuring their scattering strength for the first time and demonstrating that they scatter light more efficiently than any other low-refractive-index material yet known.

“These scales have a structure that is truly complex since it gives rise to something that is more than the sum of its parts,” said co-author Dr Matteo Burresi of the Italian National Institute of Optics in Florence. “Our simulations show that a randomly packed collection of its constituent elements by itself is not sufficient to achieve the degree of brightness that we observe.”

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

Bright-White Beetle Scales Optimise Multiple Scattering of Light by Matteo Burresi, Lorenzo Cortese, Lorenzo Pattelli, Mathias Kolle, Peter Vukusic, Diederik S. Wiersma, Ullrich Steiner, & Silvia Vignolini.  Scientific Reports 4, Article number: 6075 doi:10.1038/srep06075 Published 15 August 2014

This paper is open access.

A rose by any other name: water pinning nanostructures and wettability

There are two items about rose petals as bioinspiration for research in this posting. The first being the most recent research where scientists in Singapore have made an ultrathin film modeled on rose petals. From an Aug. 13, 2014 news item on Nanowerk (Note: A link has been removed),

A*STAR [based in Singapore] researchers have used nanoimprinting methods to make patterned polymeric films with surface topography inspired by that of a rose petal, producing a range of transparent films with high water pinning forces (“Bioinspired Ultrahigh Water Pinning Nanostructures”).

An Aug. 13, 2014 A*STAR news highlight, which originated the news item, describes the nature of the research,

A surface to which a water droplet adheres, even when it is turned upside down, is described as having strong water pinning characteristics. A rose petal and a lotus leaf are both superhydrophobic, yet dissimilarities in their water pinning properties cause a water droplet to stick to a rose petal but roll off a lotus leaf. The two leaf types differ in their micro- and nanoscale surface topography and it is these topographical details that alter the water pinning force. The rose petal has almost uniformly distributed, conical-shaped microscale protrusions with nanoscale folds on these protrusions, while the lotus leaf has randomly distributed microscale protrusions.

The imprinted surfaces developed by Jaslyn Law and colleagues at the A*STAR Institute of Materials Research and Engineering and the Singapore University of Technology and Design have uniformly distributed patterns of nanoscale protrusions that are either conical or parabolic in shape. The researchers found that the water pinning forces on these continuously patterned surfaces were much greater than on non-patterned surfaces and surfaces composed of isolated nanopillared structures or nanoscale gratings. They could then achieve high water pinning forces by patterning the nanoprotrusions onto polymeric films with a range of different non-patterned hydrophobicities, including polycarbonate, poly(methyl methacrylate) and polydimethylsiloxane (see image).

“Other methods that recreate the water pinning effect have used actual rose petals as the mold, but unless special care is taken, there are likely to be defects and inconsistencies in the recreated pattern,” says co-author Andrew Ng. “While bottom-up approaches for making patterns — for example, laser ablation, liquid flame spray or chemical vapor deposition — are more consistent, these methods are limited in the types of patterns that can be used and the scale at which a substrate can be patterned.”

In contrast, nanoimprinting methods are capable of fabricating versatile and large-scale surfaces, and can be combined with roll-to-roll techniques, hence potentially enabling more commercial applications.

The patterned polycarbonate surfaces were also shown to reduce the ‘coffee-ring’ effect: the unevenly deposited film left behind upon the evaporation of a solute-laden droplet. This mitigation of the coffee-ring effect may assist microfluidic technologies and, more generally, the patterned surfaces could be used in arid regions for dew collection or in anti-drip applications such as in greenhouses.

The study which was published online in Dec. 2013, was featured in a Jan. 22, 2014 article by Katherine Bourzac for C&EN (Chemistry and Engineering News),

In the early morning, dew clings to rose petals; when the sun rises, the dewdrops act like tiny lenses, making diffraction patterns that attract pollinating insects, says Jaslyn Bee Khuan Law, a materials scientist at the Agency for Science, Technology, and Research (A*STAR), in Singapore. A drop of water will cling to a rose petal even when it’s tilted or held upside down. The petals can hold onto these droplets because their surfaces consist of closely packed conical structures a few micrometers across. These microscale surface patterns tweak the surface tension of the water droplets, causing them to cling to the petals.

But none of these fabrication methods are amenable to large-scale, low-cost manufacturing, preventing commercialization of the water-clinging surfaces. So Law turned to a specialty of her lab: nanoimprint lithography. This printing method utilizes metal or silicon drums molded with nanoscale features on their surfaces. When the molds are heated and pressed against sheets of plastic, the plastic is embossed with the nanoscale pattern. This roll-to-roll printing process resembles the way newspapers are printed. It’s capable of producing large-area films in a short amount of time.

Water droplets easily slid off plastic films patterned with simple nanoscale gratings; isolated nanoscale pillars hung onto water slightly better. But the films with the best properties consisted of tightly packed cones about 300 nm tall. Plastic patterned with these structures could hold onto water droplets as massive as 69 mg. The team could print a 110- by 65-mm sheet of this plastic film at a speed of 10 m per minute. Currently, the dimensions of the films are limited by the size of the premade molds, Law says.

While the Singapore group has made good progress on manufacturing these materials, very basic, vexing questions about how water clings to these surfaces remain, Hayes says. For example, very small changes in the surface’s roughness can switch it from water-pinning to super hydrophobic, and researchers don’t have a detailed understanding of why.

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

Bioinspired Ultrahigh Water Pinning Nanostructures by Jaslyn Bee Khuan Law, Andrew Ming Hua Ng, Ai Yu He, and Hong Yee Low. Langmuir, 2014, 30 (1), pp 325–331 DOI: 10.1021/la4034996 Publication Date (Web): December 20, 2013
Copyright © 2013 American Chemical Society

This paper appears to be open access (I was able to access it by clicking on the HTML option).

Finally, here’s an image supplied by the A*Star researchers to illustrate their work,

[downloaded from http://pubs.acs.org/doi/full/10.1021/la4034996]

[downloaded from http://pubs.acs.org/doi/full/10.1021/la4034996]

This second rose petal item comes from Australia and dates from Fall 2013. From a Sept. 18, 2013 news item on ScienceDaily,

A new nanostructured material with applications that could include reducing condensation in airplane cabins and enabling certain medical tests without the need for high tech laboratories has been developed by researchers at the University of Sydney [Australia].

“The newly discovered material uses raspberry particles — so-called because of their appearance — which can trap tiny water droplets and prevent them from rolling off surfaces, even when that surface is turned upside down,” said Dr Andrew Telford from the University’s School of Chemistry and lead author of the research recently published in the journal, Chemistry of Materials.

The ability to immobilise [pin] very small droplets on a surface is, according to Dr Telford, a significant achievement with innumerable potential applications.

A Sept. 17, 2013 University of Sydney news release, which originated the news item, provides more insight into the research where the scientists have focused on ‘raspberry particles’ which could also be described as the ‘conical structures’ mentioned in the A*STAR work to achieve what appear to be similar ends,

Raspberry particles mimic the surface structure of some rose petals.

“Water droplets bead up in a spherical shape on top of rose petals,” Dr Telford said. “This is a sign the flower is highly water repellent.”

The reasons for this are complex and largely due to the special structure of the rose petal’s surface. The research team replicated the rose petal by assembling raspberry particles in the lab using spherical micro- and nanoparticles.

The result is that water droplets bead up when placed on films of the raspberry particles and they’re not able to drip down from it, even when turned upside down.

“Raspberry particle films can be described as sticky tape for water droplets,” Dr Telford said.

This could be useful in preventing condensation issues in airplane cabins. It could also help rapidly process simple medical tests on free-standing droplets, with the potential for very high turnover of tests with inexpensive equipment and in remote areas.

Other exciting applications are under study: if we use this nanotechnology to control how a surface is structured we can influence how it will interact with water.

“This means we will be able to design a surface that does whatever you need it to do.

“We could also design a surface that stays dry forever, never needs cleaning or able to repel bacteria or even prevent mould and fungi growth.

“We could then tweak the same structure by changing its composition so it forces water to spread very quickly.

“This could be used on quick-dry walls and roofs which would also help to cool down houses.

“This can only be achieved with a very clear understanding of the science behind the chemical properties and construction of the surface,” he said.

The discovery is also potentially viable commercially.

“Our team’s discovery is the first that allows for the preparation of raspberry particles on an industrial scale and we are now in a position where we can prepare large quantities of these particles without the need to build special plants or equipment,” Dr Telford said.

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

Mimicking the Wettability of the Rose Petal using Self-assembly of Waterborne Polymer Particles by A. M. Telford, B. S. Hawkett, C. Such, and C. Neto. Chem. Mater., 2013, 25 (17), pp 3472–3479 DOI: 10.1021/cm4016386 Publication Date (Web): July 23, 2013
Copyright © 2013 American Chemical Society

This paper is behind a paywall.

A butterfly kind of day: changing structural colour in six generations and developing fluidic devices

I have two items concerning butterflies. The first is a bioengineering project at Yale University where they changed the colour of a butterfly’s wings from brown to violet (from an Aug. 5, 2014 news item on ScienceDaily),

Yale University scientists have chosen the most fleeting of mediums for their groundbreaking work on biomimicry: They’ve changed the color of butterfly wings.

In so doing, they produced the first structural color change in an animal by influencing evolution. The discovery may have implications for physicists and engineers trying to use evolutionary principles in the design of new materials and devices.

An Aug.5, 2014 Yale University news release (also on EurekAlert), which originated the news item,

“What we did was to imagine a new target color for the wings of a butterfly, without any knowledge of whether this color was achievable, and selected for it gradually using populations of live butterflies,” said Antónia Monteiro, a former professor of ecology and evolutionary biology at Yale, now at the National University of Singapore.

In this case, Monteiro and her team changed the wing color of the butterfly Bicyclus anynana from brown to violet. They needed only six generations of selection.

The news release goes on to explain the interest in structural colour,

Little is known about how structural colors in nature evolved, although researchers have studied such mechanisms extensively in recent years. Most attempts at biomimicry involve finding a desirable outcome in nature and simply trying to copy it in the laboratory.

“Today, materials engineers are making complex materials to perform multiple functions. The parameter space for the design of such materials is huge, so it is not easy to search for the optimal design,” said Hui Cao, chair of Yale’s Department of Applied Physics, who also worked on the study. “This is why we can learn from nature, which has obtained the optimal solutions in many cases via natural evolution over millions of years.”

Indeed, the scientists explained, natural selection algorithms can select for multiple characteristics simultaneously — which is standard operating procedure in the natural world.

A bit of technical information is also included in the news release,

The desired color for the butterfly wings was achieved by changing the relative thickness of the wing scales — specifically, those of the lower lamina. It took less than a year of selective breeding to produce the color change from brown to violet.

One reason Bicyclus anynana was chosen for the experiment, Monteiro said, was because it has cousin species that have evolved violet colors on their wings twice independently. By reproducing such a change in the lab, the Yale team showed that butterfly populations harbor high levels of genetic variation regulating scale thickness that lets them react quickly to new selective conditions.

“We just thought if natural selection has been able to modify wing colors in members of this genus of butterfly, perhaps so can we,” Monteiro said.

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

Artificial selection for structural color on butterfly wings and comparison with natural evolution by Bethany R. Wasik, Seng Fatt Liew, David A. Lilien, April J. Dinwiddie, Heeso Noh, Hui Cao, and Antónia Monteiro. PNAS doi: 10.1073/pnas.1402770111 Published online August 4, 2014

This seems to be an open access paper (I was able to access the six page paper, albeit in a small font, by clicking on an Adobe reader icon).

I have not been able to find an image of the newly violet-coloured Bicyclus anynana butterfly but Yale University has provided an image of the pre-bioengineered version,

This image shows a male Bicyclus anynana, prior to the wing color change. (Below) This image shows the color change from brown to violet, over six generations of breeding. (Photographs courtesy of Antónia Monteiro)

This image shows a male Bicyclus anynana, prior to the wing color change. (Below) This image shows the color change from brown to violet, over six generations of breeding. (Photographs courtesy of Antónia Monteiro)

One of my favourite pieces on structural colour was written for The Scientist and was featured here in a Feb. 7, 2013 posting. Interestingly, Yale University is mentioned in that posting too.

This second butterfly piece focuses on its feeding habits and possible medical applications. From an Aug. 5, 2014 news item on ScienceDaily,

New discoveries about how butterflies feed could help engineers develop tiny probes that siphon liquid out of single cells for a wide range of medical tests and treatments, according to Clemson University researchers.

The National Science Foundation recently awarded the project $696,514. It was the foundation’s third grant to the project, bringing the total since 2009 to more than $3 million.

The research has brought together Clemson’s materials scientists and biologists who have been focusing on the proboscis, the mouthpart that many insects used for feeding.

For materials scientists, the goal is to develop what they call “fiber-based fluidic devices,” among them probes that could eventually allow doctors to pluck a single defective gene out of a cell and replace it with a good one, said Konstantin Kornev, a Clemson materials physics professor. “If someone were programmed to have an illness, it would be eliminated,” he said.

An Aug. 5, 2014 Clemson University media release by Paul Alongi (also on EurekAlert), which originated the news item, explains that this latest research is one of the first steps in a long journey,

… Much remains unknown about how insects use tiny pores and channels in the proboscis to sample and handle fluid.

“It’s like the proverbial magic well,” said Clemson entomology professor Peter Adler. “The more we learn about the butterfly proboscis, the more it has for us to learn about it.”

Kornev said he was attracted to butterflies for their ability to draw various kinds of liquids.

“It can be very thick like nectar and honey or very thin like water,” he said. “They do that easily. That’s a challenge for engineers.”

Researchers want the probe to be able to take fluid out of a single cell, which is 10 times smaller than the diameter of a human hair, Kornev said. The probe also will need to differentiate between different types of fluids, he said.

The technology could be used for medical devices, nanobioreactors that make complex materials and flying “micro-air vehicles” the size of an insect.

“It opens up a huge number of applications,” Kornev said. “We are actively seeking collaboration with cell biologists, medical doctors and other professionals who might find this research exciting and helpful in their applications.”

The study also is breaking new ground in biology. While scientists had a fundamental idea of how butterflies feed, it was less complete than it is now, Adler said.

Scientists have long known that butterflies use the proboscis to suck up fluid, similar to how humans use a drinking straw, Adler said. But the study found that the butterfly proboscis also acts as a sponge, he said.

“It’s a dual mechanism,” Adler said. “As they move the proboscis around, it can help sponge up the liquid and then facilitate the delivery of the liquid so that it can then be sucked up.”

As part of the study, researchers observed butterflies on flowers at the Cherry Farm Insectary just south of the main campus on the shore of Hartwell Lake. Butterflies were raised in the lab and recorded on video as they fed.

Researchers are turning their attention to smaller insects, such as flies, moths and mosquitoes, but the focus will remain on the proboscis.

In the next phase of the study, researchers would like to understand how the proboscis forms.

Larvae enter the pupa without a proboscis and emerge as a butterfly with one. Understanding what happens in the pupa could help develop the probes, Adler said.

Another challenge is figuring out how to keep the probe from getting covered with organic material when it’s inserted into the body, he said.

That’s why researchers are beginning to turn their focus to an insect almost everyone else shoos away.

“It seems the flies are able to pierce an animal’s tissue, take up the blood and not get the proboscis gummed up and covered with bacteria,” Adler said.

Tanju Karanfil, associate dean of research and graduate studies in the College of Engineering and Science, said the study has underscored the importance of breaking down silos that separate researchers from different departments so they can work for the common good.

“The most interesting work happens at the intersection of disciplines,” he said. “In this case, biologists and engineers have come together with different perspectives to answer common questions.

I have a link (which takes you to a correction for the text) and a citation for the paper,

Paradox of the drinking-straw model of the butterfly proboscis by Chen-Chih Tsai, Daria Monaenkova, Charles Beard, Peter Adler, and Konstantin Kornev. J. Exp. Biol. 217, 2130-2138. Original article: doi: 10.1242/​jeb.097998 June 15, 2014 J Exp Biol 217, 2130-2138 Correction: doi: 10.1242/​jeb.109447 July 1, 2014

The article is behind a paywall but you can view the correction in its entirety.

Hummingbirds and ‘nano’ spy cameras

Hummingbird-inspired spy cameras have come a long way since the research featured in this Aug. 12, 2011 posting which includes a video of a robot camera designed to look like a hummingbird and mimic some of its extraordinary flying abilities. These days (2014) the emphasis appears to be on mimicking the abilities to a finer degree if Margaret Munro’s July 29, 2014 article for Canada.com is to be believed,

Tiny, high-end military drones are catching up with one of nature’s great engineering masterpieces.

A side-by-side comparison has found a “remarkably similar” aerodynamic performance between hummingbirds and the Black Hornet, the most sophisticated nano spycam yet.

“(The) Average Joe hummingbird” is about on par with the tiny helicopter that is so small it can fit in a pocket, says engineering professor David Lentink, at Stanford University. He led a team from Canada [University of British Columbia], the U.S. and the Netherlands [Wageningen University and Eindhoven University of Technology] that compared the birds and the machine for a study released Tuesday [July 29, 2014].

For a visual comparison with the latest nano spycam (Black Hornet), here’s the ‘hummingbird’ featured in the 2011 posting,

The  Nano Hummingbird, a drone from AeroVironment designed for the US Pentagon, would fit into any or all of those categories.

And, here’s this 2013 image of a Black Hornet Nano Helicopter inspired by hummingbirds,

Black Hornet Nano Helicopter UAVView licenseview terms Richard Watt - Photo http://www.defenceimagery.mod.uk/fotoweb/fwbin/download.dll/45153802.jpgCourtesy: Wikipedia

Black Hornet Nano Helicopter UAVView licenseview terms
Richard Watt – Photo http://www.defenceimagery.mod.uk/fotoweb/fwbin/download.dll/45153802.jpg Courtesy: Wikipedia

A July 30, 2014 Stanford University news release by Bjorn Carey provides more details about this latest research into hummingbirds and their flying ways,

More than 42 million years of natural selection have turned hummingbirds into some of the world’s most energetically efficient flyers, particularly when it comes to hovering in place.

Humans, however, are gaining ground quickly. A new study led by David Lentink, an assistant professor of mechanical engineering at Stanford, reveals that the spinning blades of micro-helicopters are about as efficient at hovering as the average hummingbird.

The experiment involved spinning hummingbird wings – sourced from a pre-existing museum collection – of 12 different species on an apparatus designed to test the aerodynamics of helicopter blades. The researchers used cameras to visualize airflow around the wings, and sensitive load cells to measure the drag and the lift force they exerted, at different speeds and angles.

Lentink and his colleagues then replicated the experiment using the blades from a ProxDynamics Black Hornet autonomous microhelicopter. The Black Hornet is the most sophisticated microcopter available – the United Kingdom’s army uses it in Afghanistan – and is itself about the size of a hummingbird.

Even spinning like a helicopter, rather than flapping, the hummingbird wings excelled: If hummingbirds were able to spin their wings to hover, it would cost them roughly half as much energy as flapping. The microcopter’s wings kept pace with the middle-of-the-pack hummingbird wings, but the topflight wings – those of Anna’s hummingbird, a species common throughout the West Coast – were still about 27 percent more efficient than engineered blades.

Hummingbirds acing the test didn’t particularly surprise Lentink – previous studies had indicated hummingbirds were incredibly efficient – but he was impressed with the helicopter.

“The technology is at the level of an average Joe hummingbird,” Lentink said. “A helicopter is really the most efficient hovering device that we can build. The best hummingbirds are still better, but I think it’s amazing that we’re getting closer. It’s not easy to match their performance, but if we build better wings with better shapes, we might approximate hummingbirds.”

Based on the measurements of Anna’s hummingbirds, Lentink said there is potential to improve microcopter rotor power by up to 27 percent.

The high-fidelity experiment also provided an opportunity to refine previous rough estimates of muscle power. Lentink’s team learned that hummingbirds’ muscles produce a surprising 130 watts of energy per kilogram; the average for other birds, and across most vertebrates, is roughly 100 watts/kg.

Although the current study revealed several details of how a hummingbird hovers in one place, the birds still hold many secrets. For instance, Lentink said, we don’t know how hummingbirds maintain their flight in a strong gust, how they navigate through branches and other clutter, or how they change direction so quickly during aerial “dogfights.”

He also thinks great strides could be made by studying wing aspect ratios, the ratio of wing length to wing width. The aspect ratios of all the hummingbirds’ wings remarkably converged around 3.9. The aspect ratios of most wings used in aviation measure much higher; the Black Hornet’s aspect ratio was 4.7.

“I want to understand if aspect ratio is special, and whether the amount of variation has an effect on performance,” Lentink said. Understanding and replicating these abilities and characteristics could be a boon for robotics and will be the focus of future experiments.

“Those are the things we don’t know right now, and they could be incredibly useful. But I don’t mind it, actually,” Lentink said. “I think it’s nice that there are still a few things about hummingbirds that we don’t know.”

Agreed, it’s nice to know there are still a few mysteries left. You can watch the ‘mysterious’ hummingbird in this video courtesy of the Rivers Ingersoll Lentink Lab at Stanford University,

High speed video of Anna’s hummingbird at Stanford Arizona Cactus Garden.

Here’s a link to and a citation for the paper, H/T to Nancy Owano’s article on phys.org for alerting me to this story.

Hummingbird wing efficacy depends on aspect ratio and compares with helicopter rotors by Jan W. Kruyt, Elsa M. Quicazán-Rubio, GertJan F. van Heijst, Douglas L. Altshuler, and David Lentink.  J. R. Soc. Interface 6 October 2014 vol. 11 no. 99 20140585 doi: 10.1098/​rsif.2014.0585 Published [online] 30 July 2014

This is an open access paper.

Despite Munro’s reference to the Black Hornet as a ‘nano’ spycam, the ‘microhelicopter’ description in the news release places the device at the microscale (/1,000,000,000). Still, I don’t understand what makes it microscale since it’s visible to the naked eye. In any case, it is small.

Darwin’s barnacles become unglued

The world’s strongest glue comes from barnacles and those creatures have something to teach us. From a July 18, 2014 news item on Nanowerk,

Over a 150 years since it was first described by Darwin, scientists are finally uncovering the secrets behind the super strength of barnacle glue.

Still far better than anything we have been able to develop synthetically, barnacle glue – or cement – sticks to any surface, under any conditions.

But exactly how this superglue of superglues works has remained a mystery – until now.

An international team of scientists led by Newcastle University, UK, and funded by the US Office of Naval Research, have shown for the first time that barnacle larvae release an oily droplet to clear the water from surfaces before sticking down using a phosphoprotein adhesive.

A July 18, 2014 Newcastle University (UK) press release, which originated the news item, provides some context and describes the research,

“It’s over 150 years since Darwin first described the cement glands of barnacle larvae and little work has been done since then,” says Dr Aldred, a research associate in the School of Marine Science and Technology at Newcastle University, one of the world’s leading institutions in this field of research.

“We’ve known for a while there are two components to the bioadhesive but until now, it was thought they behaved a bit like some of the synthetic glues – mixing before hardening.  But that still left the question, how does the glue contact the surface in the first place if it is already covered with water?  This is one of the key hurdles to developing glues for underwater applications.

“Advances in imaging techniques, such as 2-photon microscopy, have allowed us to observe the adhesion process and characterise the two components. We now know that these two substances play very different roles – one clearing water from the surface and the other cementing the barnacle down.

“The ocean is a complex mixture of dissolved ions, the pH varies significantly across geographical areas and, obviously, it’s wet.  Yet despite these hostile conditions, barnacle glue is able to withstand the test of time.

“It’s an incredibly clever natural solution to this problem of how to deal with a water barrier on a surface it will change the way we think about developing bio-inspired adhesives that are safe and already optimised to work in conditions similar to those in the human body, as well as marine paints that stop barnacles from sticking.”

Barnacles have two larval stages – the nauplius and the cyprid.  The nauplius, is common to most crustacea and it swims freely once it hatches out of the egg, feeding in the plankton.

The final larval stage, however, is the cyprid, which is unique to barnacles.  It investigates surfaces, selecting one that provides suitable conditions for growth. Once it has decided to attach permanently, the cyprid releases its glue and cements itself to the surface where it will live out the rest of its days.

“The key here is the technology.  With these new tools we are able to study processes in living tissues, as they happen. We can get compositional and molecular information by other methods, but they don’t explain the mechanism.  There’s no substitute for seeing things with your own eyes. ” explains Dr Aldred.

“In the past, the strong lasers used for optically sectioning biological samples have typically killed the samples, but now technology allows us to study life processes exactly as they would happen in nature.”

The press release also notes some possible applications for these research findings (Note: Links have been removed),

Publishing their findings this week in the prestigious academic journal Nature Communications, author Dr Nick Aldred says the findings could pave the way for the development of novel synthetic bioadhesives for use in medical implants and micro-electronics.  The research will also be important in the production of new anti-fouling coatings for ships.

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

Synergistic roles for lipids and proteins in the permanent adhesive of barnacle larvae by Neeraj V. Gohad, Nick Aldred, Christopher M. Hartshorn, Young Jong Lee, Marcus T. Cicerone, Beatriz Orihuela, Anthony S. Clare, Dan Rittschof, & Andrew S. Mount. Nature Communications 5, Article number: 4414 doi:10.1038/ncomms5414 Published 11 July 2014

This paper is behind a paywall although a free preview is 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,