Category Archives: biomimcry

The challenges of wet adhesion and how nature solves the problem

I usually post about dry adhesion, that is, sticking to dry surfaces in the way a gecko might. This particular piece concerns wet adhesion, a matter of particular interest in medicine where you want bandages and such to stick to a wet surface and in marine circles where they want barnacles and such to stop adhering to boat and ship hulls.

An Aug. 6, 2015 news item on ScienceDaily touts ‘wet adhesion’ research focused on medicinal matters,

Wet adhesion is a true engineering challenge. Marine animals such as mussels, oysters and barnacles are naturally equipped with the means to adhere to rock, buoys and other underwater structures and remain in place no matter how strong the waves and currents.

Synthetic wet adhesive materials, on the other hand, are a different story.

Taking their cue from Mother Nature and the chemical composition of mussel foot proteins, the Alison Butler Lab at UC [University of California] Santa Barbara [UCSB] decided to improve a small molecule called the siderophore cyclic trichrysobactin (CTC) that they had previously discovered. They modified the molecule and then tested its adhesive strength in aqueous environments. The result: a compound that rivals the staying power of mussel glue.

An Aug. 6, 2015 UCSB news release by Julie Cohen, which originated the news item, describes some of the reasons for the research, the interdisciplinary aspect of the collaboration, and technical details of the work (Note: Links have been removed),

“There’s real need in a lot of environments, including medicine, to be able to have glues that would work in an aqueous environment,” said co-author Butler, a professor in UCSB’s Department of Chemistry and Biochemistry. “So now we have the basis of what we might try to develop from here.”

Also part of the interdisciplinary effort were Jacob Israelachvili’s Interfacial Sciences Lab in UCSB’s Department of Chemical Engineering and J. Herbert Waite, a professor in the Department of Molecular, Cellular and Developmental Biology, whose own work focuses on wet adhesion.

“We just happened to see a visual similarity between compounds in the siderophore CTC and in mussel foot proteins,” Butler explained. Siderophores are molecules that bind and transport iron in microorganisms such as bacteria. “We specifically looked at the synergy between the role of the amino acid lysine and catechol,” she added. “Both are present in mussel foot proteins and in CTC.”
Mussel foot proteins contain similar amounts of lysine and the catechol dopa. Catechols are chemical compounds used in such biological functions as neurotransmission. However, certain proteins have adopted dopa for adhesive purposes.

From discussions with Waite, Butler realized that CTC contained not only lysine but also a compound similar to dopa. Further, CTC paired its catechol with lysine, just like mussel foot proteins do.

“We developed a better, more stable molecule than the actual CTC,” Butler explained. “Then we modified it to tease out the importance of the contributions from either lysine or the catechol.”

Co-lead author Greg Maier, a graduate student in the Butler Lab, created six different compounds with varying amounts of lysine and catechol. The Israelachvili lab tested each compound for its surface and adhesion characteristics. Co-lead author Michael Rapp used a surface force apparatus developed in the lab to measure the interactions between mica surfaces in a saline solution.

Only the two compounds containing a cationic amine, such as lysine, and catechol exhibited adhesive strength and a reduced intervening film thickness, which measures the amount two surfaces can be squeezed together. Compounds without catechol had greatly diminished adhesion levels but a similarly reduced film thickness. Without lysine, the compounds displayed neither characteristic. “Our tests showed that lysine was key, helping to remove salt ions from the surface to allow the glue to get to the underlying surface,” Maier said.

“By looking at a different biosystem that has similar characteristics to some of the best-performing mussel glues, we were able to deduce that these two small components work together synergistically to create a favorable environment at surfaces to promote adherence,” explained Rapp, a chemical engineering graduate student. “Our results demonstrate that these two molecular groups not only prime the surface but also work collectively to build better adhesives that stick to surfaces.”

“In a nutshell, our discovery is that you need lysine and you need the catechol,” Butler concluded. “There’s a one-two punch: the lysine clears and primes the surface and the catechol comes down and hydrogen bonds to the mica surface. This is an unprecedented insight about what needs to happen during wet adhesion.”

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

Adaptive synergy between catechol and lysine promotes wet adhesion by surface salt displacement by Greg P. Maier, Michael V. Rapp, J. Herbert Waite, Jacob N. Israelachvili, and Alison Butler. Science 7 August 2015: Vol. 349 no. 6248 pp. 628-632 DOI: 10.1126/science.aab055

This paper is behind a paywall.

I have previously written about mussels and wet adhesion in a Dec. 13, 2012 posting regarding some research at the University of British Columbia (Canada). As for dry adhesion, there’s my June 11, 2014 posting titled: Climb like a gecko (in DARPA’s [US Defense Advanced Research Projects Agency] Z-Man program) amongst others.

Building nanocastles in the sand

Scientists have taken inspiration from sandcastles to build robots made of nanoparticles. From an Aug. 5, 2015 news item on ScienceDaily,

If you want to form very flexible chains of nanoparticles in liquid in order to build tiny robots with flexible joints or make magnetically self-healing gels, you need to revert to childhood and think about sandcastles.

In a paper published this week in Nature Materials, researchers from North Carolina State University and the University of North Carolina-Chapel Hill show that magnetic nanoparticles encased in oily liquid shells can bind together in water, much like sand particles mixed with the right amount of water can form sandcastles.

An Aug. 5, 2015 North Carolina State University (NCSU) news release (also on EurekAlert) by Mick Kulikowski, which originated the news item, expands on the theme,

“Because oil and water don’t mix, the oil wets the particles and creates capillary bridges between them so that the particles stick together on contact,” said Orlin Velev, INVISTA Professor of Chemical and Biomolecular Engineering at NC State and the corresponding author of the paper.

“We then add a magnetic field to arrange the nanoparticle chains and provide directionality,” said Bhuvnesh Bharti, research assistant professor of chemical and biomolecular engineering at NC State and first author of the paper.

Chilling the oil is like drying the sandcastle. Reducing the temperature from 45 degrees Celsius to 15 degrees Celsius freezes the oil and makes the bridges fragile, leading to breaking and fragmentation of the nanoparticle chains. Yet the broken nanoparticles chains will re-form if the temperature is raised, the oil liquefies and an external magnetic field is applied to the particles.

“In other words, this material is temperature responsive, and these soft and flexible structures can be pulled apart and rearranged,” Velev said. “And there are no other chemicals necessary.”

The paper is also co-authored by Anne-Laure Fameau, a visiting researcher from INRA [French National Institute for Agricultural Research or Institut National de la Recherche Agronomique], France. …

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

Nanocapillarity-mediated magnetic assembly of nanoparticles into ultraflexible filaments and reconfigurable networks by Bhuvnesh Bharti, Anne-Laure Fameau, Michael Rubinstein, & Orlin D. Velev. Nature Materials (2015) doi:10.1038/nmat4364 Published online 03 August 2015

This paper is behind a paywall.

Pancake bounce

What impact does a droplet make on a solid surface? It’s not the first question that comes to my mind but scientists have been studying it for over a century. From an Aug. 5, 2015 news item on Nanowerk (Note: A link has been removed),

Studies of the impact a droplet makes on solid surfaces hark back more than a century. And until now, it was generally believed that a droplet’s impact on a solid surface could always be separated into two phases: spreading and retracting. But it’s much more complex than that, as a team of researchers from City University of Hong Kong, Ariel University in Israel, and Dalian University of Technology in China report in the journal Applied Physics Letters, from AIP Publishing (“Controlling drop bouncing using surfaces with gradient features”).

An Aug. 4, 2015 American Institute of Physics news release (also on EurekAlert), which originated the news item, describes the impact in detail,

“During the spreading phase, the droplet undergoes an inertia-dominant acceleration and spreads into a ‘pancake’ shape,” explained Zuankai Wang, an associate professor within the Department of Mechanical and Biomedical Engineering at the City University of Hong Kong. “And during the retraction phase, the drop minimizes its surface energy and pulls back inward.”

Remarkably, on gold standard superhydrophobic–a.k.a. repellant–surfaces such as lotus leaves, droplets jump off at the end of the retraction stage due to the minimal energy dissipation during the impact process. This is attributed to the presence of an air cushion within the rough surface.

There exists, however, a classical limit in terms of the contact time between droplets and the gold standard superhydrophobic materials inspired by lotus leaves.

As the team previously reported in the journal Nature Physics, it’s possible to shape the droplet to bounce from the surface in a pancake shape directly at the end of the spreading stage without going through the receding process. As a result, the droplet can be shed away much faster.

“Interestingly, the contact time is constant under a wide range of impact velocities,” said Wang. “In other words: the contact time reduction is very efficient and robust, so the novel surface behaves like an elastic spring. But the real magic lies within the surface texture itself.”

To prevent the air cushion from collapsing or water from penetrating into the surface, conventional wisdom suggests the use of nanoscale posts with small inter-post spacings. “The smaller the inter-post spacings, the greater the impact velocity the small inter-post can withstand,” he elaborated. “By contrast, designing a surface with macrostructures–tapered sub-millimeter post arrays with a wide spacing–means that a droplet will shed from it much faster than any previously engineered materials.”

What the New Results Show

Despite exciting progress, rationally controlling the contact time and quantitatively predicting the critical Weber number–a number used in fluid mechanics to describe the ratio between deforming inertial forces and stabilizing cohesive forces for liquids flowing through a fluid medium–for the occurrence of pancake bouncing remained elusive.

So the team experimentally demonstrated that the drop bouncing is intricately influenced by the surface morphology. “Under the same center-to-center post spacing, surfaces with a larger apex angle can give rise to more pancake bouncing, which is characterized by a significant contact time reduction, smaller critical Weber number, and a wider Weber number range,” according to co-authors Gene Whyman and Edward Bormashenko, both professors at Ariel University.

Wang and colleagues went on to develop simple harmonic spring models to theoretically reveal the dependence of timescales associated with the impinging drop and the critical Weber number for pancake bouncing on the surface morphology. “The insights gained from this work will allow us to rationally design various surfaces for many practical applications,” he added.

The team’s novel surfaces feature a shortened contact time that prevents or slows ice formation. “Ice formation and its subsequent buildup hinder the operation of modern infrastructures–including aircraft, offshore oil platforms, air conditioning systems, wind turbines, power lines, and telecommunications equipment,” Wang said.

At supercooled temperatures, which involves lowering the temperature of a liquid or gas below its freezing point without it solidifying, the longer a droplet remains in contact with a surface before bouncing off the greater the chances are of it freezing in place. “Our new surface structure can be used to help prevent aircraft wings and engines from icing,” he said.

This is highly desirable, because a very light coating of snow or ice–light enough to be barely visible–is known to reduce the performance of airplanes and even cause crashes. One such disaster occurred in 2009, and called attention to the dangers of in-flight icing after it caused Air France Flight 447 flying from Rio de Janeiro to Paris to crash into the Atlantic Ocean.

Beyond anti-icing for aircraft, “turbine blades in power stations and wind farms can also benefit from an anti-icing surface by gaining a boost in efficiency,” he added.

As you can imagine, this type of nature-inspired surface shows potential for a tremendous range of other applications as well–everything from water and oil separation to disease transmission prevention.

The next step for the team? To “develop bioinspired ‘active’ materials that are adaptive to their environments and capable of self-healing,” said Wang.

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

Controlling drop bouncing using surfaces with gradient features by Yahua Liu, Gene Whyman, Edward Bormashenko, Chonglei Hao, and Zuankai Wang. Appl. Phys. Lett. 107, 051604 (2015); http://dx.doi.org/10.1063/1.4927055

This paper appears to be open access.

Finally, here’s an illustration of the pancake bounce,

Droplet hitting tapered posts shows “pancake” bouncing characterized by lifting off the surface of the end of spreading without retraction. Credit- Z.Wang/HKU

Droplet hitting tapered posts shows “pancake” bouncing characterized by lifting off the surface of the end of spreading without retraction. Credit- Z.Wang/HKU

There is also a pancake bounce video which you can view here on EurekAlert.

Sunscreen based on algae, reef fish mucus, and chitosan

The proposed sunscreen is all natural and would seem to avoid some of the environmental problems associated with other sunscreens (e.g., washing off into the ocean and polluting it). From a July 29, 2015 American Chemical Society (ACS) news release (also on EurekAlert), Note: Links have been removed,

For consumers searching for just the right sunblock this summer, the options can be overwhelming. But scientists are now turning to the natural sunscreen of algae — which is also found in fish slime — to make a novel kind of shield against the sun’s rays that could protect not only people, but also textiles and outdoor materials. …

Existing sunblock lotions typically work by either absorbing ultraviolet rays or physically blocking them. A variety of synthetic and natural compounds can accomplish this. But most commercial options have limited efficiency, pose risks to the environment and human health or are not stable. To address these shortcomings, Vincent Bulone, Susana C. M. Fernandes and colleagues looked to nature for inspiration.

The researchers used algae’s natural sunscreen molecules, which can also be found in reef fish mucus and microorganisms, and combined them with chitosan, a biopolymer from crustacean shells. Testing showed their materials were biocompatible, stood up well in heat and light, and absorbed both ultraviolet A and ultraviolet B radiation with high efficiency.

The authors acknowledge funding from the European Commission Marie Curie Intra-European Fellowship, the KTH Advanced Carbohydrate Materials Consortium (CarboMat), the Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) and the Basque Government Department of Education.

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

Exploiting Mycosporines as Natural Molecular Sunscreens for the Fabrication of UV-Absorbing Green Material by Susana C. M. Fernandes, Ana Alonso-Varona, Teodoro Palomares, Verónica Zubillaga, Jalel Labidi, and Vincent Bulone.
ACS Appl. Mater. Interfaces, Article ASAP DOI: 10.1021/acsami.5b04064 Publication Date (Web): July 13, 2015
Copyright © 2015 American Chemical Society

This paper is behind a paywall.

Cleaning antennae—ant style

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Sea sapphires: now you see them, now you don’t and more about structural colour/color

The structural colour of the sea sapphire

 Scientists are studying the disappearing act of this ocean-dwelling copepod. Credit: Kaj Maney, www.liquidguru.com Courtesy: American Chemical Society


Scientists are studying the disappearing act of this ocean-dwelling copepod.
Credit: Kaj Maney, www.liquidguru.com Courtesy: American Chemical Society

Now, you’ve seen a sea sapphire. Here’s more about them and the interest they hold for experts in photonics, from a July 15, 2015 news item on ScienceDaily,

Sapphirina, or sea sapphire, has been called “the most beautiful animal you’ve never seen,” and it could be one of the most magical. Some of the tiny, little-known copepods appear to flash in and out of brilliantly colored blue, violet or red existence. Now scientists are figuring out the trick to their hues and their invisibility. The findings appear in the Journal of the American Chemical Society and could inspire the next generation of optical technologies.

A July 15, 2015 American Chemical Society (ACS) news release, which originated the news item, provides more detail,

Copepods are tiny aquatic crustaceans that live in both fresh and salt water. Some males of the ocean-dwelling Sapphirina genus display striking, iridescent colors that scientists think play a role in communication and mate recognition. The shimmering animals’ colors result when light bounces off of the thin, hexagonal crystal plates that cover their backs. These plates also help them vanish, if only fleetingly. Scientists didn’t know specifically what factors contributed to creating different shades. Scientists at the Weizmann Institute [Israel] and the Interuniversity Institute for Marine Sciences in Eilat [Israel] wanted to investigate the matter.

The researchers measured the light reflectance — which determines color — of live Sapphirina males and the spacing between crystal layers. They found that changes of reflectance depended on the thickness of the spacing. And for at least one particular species, when light hits an animal at a 45-degree angle, reflectance shifts out of the visible light range and into the ultraviolet, and it practically disappears. Their results could help inform the design of artificial photonic crystal structures, which have many potential uses in reflective coatings, optical mirrors and optical displays.

To sum this up, the colour and the invisibility properties are due to thin, hexagonal crystal plates and the spacing of these plates, in other words, structural colour, which is usually achieved at the nanoscale.

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

Structural Basis for the Brilliant Colors of the Sapphirinid Copepods by Dvir Gur, Ben Leshem, Maria Pierantoni, Viviana Farstey, Dan Oron, Steve Weiner, and Lia Addadi. J. Am. Chem. Soc., 2015, 137 (26), pp 8408–8411 DOI: 10.1021/jacs.5b05289 Publication Date (Web): June 22, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

For anyone who’s interested, Lynn Kimlicka has a nice explanation of structural colour in a July 22, 2015 posting on the Something About Science blog where she discusses some recent research iridescence in bird feathers and synthetic melanin. She also shares a picture of her budgie and its iridescent feathers. The ‘melanin’ research was mentioned here in a May 19, 2015 posting where I also provide a link to a great 2013 piece on structural throughout the animal and plant kingdoms by Cristina Luiggi for The Scientist.

Understanding how nanostructures can affect optical properties could be leading to new ways of managing light. A July 23, 2015 news item on ScienceDaily describes a project at the University of Delaware dedicated to “changing the color of light,”

Researchers at the University of Delaware have received a $1 million grant from the W.M. Keck Foundation to explore a new idea that could improve solar cells, medical imaging and even cancer treatments. Simply put, they want to change the color of light.

A July 23, 2015 University of Delaware (UD) news release, which originated the news item, provides more information about the proposed research,

“A ray of light contains millions and millions of individual units of light called photons,” says project leader Matthew Doty. “The energy of each photon is directly related to the color of the light — a photon of red light has less energy than a photon of blue light. You can’t simply turn a red photon into a blue one, but you can combine the energy from two or more red photons to make one blue photon.”

This process, called “photon upconversion,” isn’t new, Doty says. However, the UD team’s approach to it is.

They want to design a new kind of semiconductor nanostructure that will act like a ratchet. It will absorb two red photons, one after the other, to push an electron into an excited state when it can emit a single high-energy (blue) photon.

These nanostructures will be so teeny they can only be viewed when magnified a million times under a high-powered electron microscope.

“Think of the electrons in this structure as if they were at a water park,” Doty says. “The first red photon has only enough energy to push an electron half-way up the ladder of the water slide. The second red photon pushes it the rest of the way up. Then the electron goes down the slide, releasing all of that energy in a single process, with the emission of the blue photon. The trick is to make sure the electron doesn’t slip down the ladder before the second photon arrives. The semiconductor ratchet structure is how we trap the electron in the middle of the ladder until the second photon arrives to push it the rest of the way up.”

The UD team will develop new semiconductor structures containing multiple layers of different materials, such as aluminum arsenide and gallium bismuth arsenide, each only a few nanometers thick. This “tailored landscape” will control the flow of electrons into states with varying potential energy, turning once-wasted photons into useful energy.

The UD team has shown theoretically that their semiconductors could reach an upconversion efficiency of 86 percent, which would be a vast improvement over the 36 percent efficiency demonstrated by today’s best materials. What’s more, Doty says, the amount of light absorbed and energy emitted by the structures could be customized for a variety of applications, from lightbulbs to laser-guided surgery.

How do you even begin to make structures so tiny they can only be seen with an electron microscope? In one technique the UD team will use, called molecular beam epitaxy, nanostructures will be built by depositing layers of atoms one at a time. Each structure will be tested to see how well it absorbs and emits light, and the results will be used to tailor the structure to improve performance.

The researchers also will develop a milk-like solution filled with millions of identical individual nanoparticles, each one containing multiple layers of different materials. The multiple layers of this structure, like multiple candy shells in an M&M, will implement the photon ratchet idea. Through such work, the team envisions a future upconversion “paint” that could be easily applied to solar cells, windows and other commercial products.

Improving medical tests and treatments

While the initial focus of the three-year project will be on improving solar energy harvesting, the team also will explore biomedical applications.

A number of diagnostic tests and medical treatments, ranging from CT [computed tomography] and PET [positron emission tomography] scans to chemotherapy, rely on the release of fluorescent dyes and pharmaceutical drugs. Ideally, such payloads are delivered both at specific disease sites and at specific times, but this is hard to control in practice.

The UD team aims to develop an upconversion nanoparticle that can be triggered by light to release its payload. The goal is to achieve the controlled release of drug therapies even deep within diseased human tissue while reducing the peripheral damage to normal tissue by minimizing the laser power required.

“This is high-risk, high-reward research,” Doty says. “High-risk because we don’t yet have proof-of-concept data. High-reward because it has such a huge potential impact in renewable energy to medicine. It’s amazing to think that this same technology could be used to harvest more solar energy and to treat cancer. We’re excited to get started!”

That’s it for structural colour/color today.

Micro-supercapacitor, leaves, and Korea’s Institute for Basic Sciences

South Korea’s research on creating micro-supercapacitors (MSC) was first published online in February 2015 but it seems the researchers decided to promote the work after its print publication in May 2015.

A July 2, 2015 news item on Nanotechnology Now makes the announcement,

There was a time during the early development of portable electronics when the biggest hurdle to overcome was making the device small enough to be considered portable.  After the invention of the microprocessor in the early 1970s, miniature, portable electronics have become commonplace and ever since the next challenge has been finding an equally small and reliable power source.  Chemical batteries store a lot of energy but require a long period of time for that energy to charge and discharge plus have a limited lifespan.  Capacitors charge quickly but cannot store enough charge to work for long enough to be practical.  One possible solution is something called a solid-state micro-supercapacitor (MSC).  Supercapacitors are armed with the power of a battery and can also sustain that power for a prolonged period time.  Researchers have attempted to create MSCs in the past using various hybrids of metals and polymers but none were suitable for practical use.  In more recent trials using graphene and carbon nanotubes to make MSCs, the results were similarly lackluster.

An international team of researchers led by Young Hee Lee, including scientists from the Center for Integrated Nanostructure Physics at the Institute for Basic Science (IBS) and Department of Energy Science at Sungkyunkwan University in South Korea, has devised a new technique for creating an MSC that doesn’t have the shortcomings of previous attempts but instead delivers high electrochemical performance.

A June 29, 2015 South Korea Institute for Basic Science (IBS) press release by Daniel Kopperud, which originated the news item, reveals this research is bioinspired,

When designing something new and complex, sometimes the best inspiration is one already found in nature.  The team modeled their MSC film structure on natural vein-textured leaves in order to take advantage of the natural transport pathways which enable efficient ion diffusion parallel to the graphene planes found within them.

To create this final, efficient shape, the team layered a graphene-hybrid film with copper hydroxide nanowires.  After many alternating layers they achieved the desired thickness, and added an acid solution to dissolve the nanowires so that a thin film with nano-impressions was all that remained.

To fabricate the MSCs the film was applied to a plastic layer with thin, ~5μm long parallel gold strips placed on top.  Everything not covered by the gold strips was chemically etched away so that only the gold strips on top of a layer of film were left.  Gold contact pads perpendicular to the gold strips were added and a conductive gel filled in the remaining spaces and was allowed to solidify.  Once peeled from the plastic layer, the finished MSCs resemble clear tape with gold electrical leads on opposite sides.

The team produced stunning test results. In addition to its superior energy density, the film is highly flexible and actually increases capacitance after initial use.  The volumetric energy density was 10 times higher than currently available commercial supercapacitors and also far superior to any other recent research.  The MSCs are displaying electrical properties about five orders of magnitude higher than similar lithium batteries and are comparable to existing, larger supercapacitors.  According to Lee, “To our knowledge, the volumetric energy density and the maximum volumetric power density in our work are the highest values among all carbon-based solid-state MSCs reported to date.”

In the future, consumers will likely power their devices with MSCs instead of batteries.  Applications for light, reliable energy storage combined with a long lifespan and fast charge/discharge time.  The team’s MSCs could be embedded into an electronic circuit chip as power sources for practical applications such as implantable medical devices, active radio frequency identification tags, and micro robots.  If engineers utilize the material’s incredible flexibility, these MSCs could be utilized in portable, stretchable, and even wearable electronic devices.

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

Leaf Vein-Inspired Nanochanneled Graphene Film for Highly Efficient Micro-Supercapacitors by Jian Chang, Subash Adhikari, Tae Hoon Lee, Bing Li, Fei Yao, Duy Tho Pham, Viet Thong Le, and Young Hee Lee. Advanced Energy Materials, Volume 5, Issue 9, May 6, 2015 First published online Feb. 20, 2015 DOI: 10.1002/aenm.201500003

This paper is behind a paywall.

Reducing friction with snakeskin-inspired surface

A June 30, 2015 Institute of Physics press release (also on EurekAlert) explains how snakeskin may inspire a whole new generation of robots bound for outer space along with other more earth-bound applications,

Snakeskin-inspired surfaces smash records, providing an astonishing 40% friction reduction in tests of high performance materials.

These new surfaces could improve the reliability of mechanical components in machines such as high performance cars and add grist to the mill of engineers designing a new generation of space exploration robots.

The skin of many snakes and lizards has been studied by biologists and has long been known to provide friction reduction to the animal as it moves. It is also resistant to wear, particularly in environments that are dry and dusty or sandy.

Dr Greiner and his team used a laser to etch the surface of a steel pin so that it closely resembled the texture of snakeskin. They then tested the friction created when the pin moved against another surface.

In dry conditions, i.e. with no oil or other lubricant, the scale-like surface created far less friction – 40% less – than its smooth counterpart.

Lead researcher Dr Christian Greiner said: “If we’d managed just a 1% reduction in friction, our engineering colleagues would have been delighted; 40% really is a leap forward and everyone is very excited.”

Applications are likely to be in mechanical devices that are made to a micro or nano scale. Familiar examples include the sensors in car anti-lock braking systems, computer hard disk drives, and accelerometers in mobile phones, which enable the device to determine for example whether it’s in portrait or landscape mode.

“Our new surface texture will mainly come into its own when engineers are really looking to push the envelope,” Dr Greiner said.

The snakeskin surface could be used in very high-end automotive engineering, such as Formula 1 racing cars. It could also be used in highly sensitive scientific equipment, including sensors installed in synchrotrons such as the Diamond Light Source in the UK or the Large Hadron Collider in Switzerland, and anywhere the engineering challenge is to further miniaturise moving parts.

There is interest in snakeskin-inspired materials from the robotics sector, too, which is designing robots inspired by snakes, which could aid exploration of very dusty environments, including those in space. This raises a new challenge for Dr Greiner’s team: to make a material that decreases friction in only one direction.

Anyone who has felt snakeskin will know that the scales all lie in the same direction and are articulated to aid the snake in its forward motion, while resisting backwards motion. The steel pins tested in this research mimic only the overall surface texture of snakeskin and reduce friction in at least two directions. Dr Greiner has made some progress with polymers that even more closely mimic snakeskin to reduce friction in only one direction. It is, he says, early days and this later work is not yet scheduled for publication.

The only caution is that this new surface doesn’t work well in an environment where oil or another lubricant is present. In fact, the snakeskin effect created three times more friction with lubricant than an equivalent smooth surface.

“This wasn’t a huge surprise,” Dr Greiner explained, “since we were looking to nature for inspiration and the species we mimicked – the royal python and a lizard called a sandfish skink – live in very dry environments and don’t secrete oils or other liquids onto their skin.”

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

Bio-inspired scale-like surface textures and their tribological properties by Christian Greiner and Michael Schäfer. Bioinspir. Biomim. 10 044001 doi:10.1088/1748-3190/10/4/044001 Published 30 June 2015

This paper is open access.

World’s first full-color, flexible thin-film reflective display: a step forward for camouflage?

Caption: Dr. Chanda used an iconic National Geographic photographic of an Afghan girl to demonstrate the color-changing abilities of the nanostructured reflective display developed by his team. Credit: University of Central Florida, used with permission from National Geographic

Caption: Dr. Chanda used an iconic National Geographic photographic of an Afghan girl to demonstrate the color-changing abilities of the nanostructured reflective display developed by his team. Credit: University of Central Florida, used with permission from National Geographic

This has gotten a lot of attention. A June 25, 2015 news item on Azonano describes a couple of possible applications,

Imagine a soldier who can change the color and pattern of his camouflage uniform from woodland green to desert tan at will. Or an office worker who could do the same with his necktie. Is someone at the wedding reception wearing the same dress as you? No problem – switch yours to a different color in the blink of an eye.

A June 24, 2015 University of Central Florida news release on EurekAlert, which originated the news item, provides some insight into the research along with some technical details,

Chanda’s [Professor Debashis Chanda] research was inspired by nature. Traditional displays like those on a mobile phone require a light source, filters and a glass plates. But animals like chameleons, octopuses and squids are born with thin, flexible, color-changing displays that don’t need a light source – their skin.

“All manmade displays – LCD, LED, CRT – are rigid, brittle and bulky. But you look at an octopus, they can create color on the skin itself covering a complex body contour, and it’s stretchable and flexible,” Chanda said. “That was the motivation: Can we take some inspiration from biology and create a skin-like display?”

As detailed in the cover article of the June issue of the journal Nature Communications, Chanda is able to change the color on an ultrathin nanostructured surface by applying voltage. The new method doesn’t need its own light source. Rather, it reflects the ambient light around it.

A thin liquid crystal layer is sandwiched over a metallic nanostructure shaped like a microscopic egg carton that absorbs some light wavelengths and reflects others. The colors reflected can be controlled by the voltage applied to the liquid crystal layer. The interaction between liquid crystal molecules and plasmon waves on the nanostructured metallic surface played the key role in generating the polarization-independent, full-color tunable display.

His method is groundbreaking. It’s a leap ahead of previous research that could produce only a limited color palette. And the display is only about few microns thick, compared to a 100-micron-thick human hair. Such an ultrathin display can be applied to flexible materials like plastics and synthetic fabrics.

The research has major implications for existing electronics like televisions, computers and mobile devices that have displays considered thin by today’s standards but monstrously bulky in comparison. But the potentially bigger impact could be whole new categories of displays that have never been thought of.

“Your camouflage, your clothing, your fashion items – all of that could change,” Chanda said. “Why would I need 50 shirts in my closet if I could change the color and pattern?”

Researchers used a simple and inexpensive nano-imprinting technique that can produce the reflective nanostructured surface over a large area.

“This is a cheap way of making displays on a flexible substrate with full-color generation,” Chanda said. “That’s a unique combination.”

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

Polarization-independent actively tunable colour generation on imprinted plasmonic surfaces by Daniel Franklin, Yuan Chen, Abraham Vazquez-Guardado, Sushrut Modak, Javaneh Boroumand, Daming Xu, Shin-Tson Wu & Debashis Chanda. Nature Communications 6, Article number: 7337 doi:10.1038/ncomms8337 Published 11 June 2015

This paper is open access.

Researchers at Karolinska Institute (Sweden) build an artificial neuron

Unlike my post earlier today (June 26, 2015) about BrainChip, this is not about neuromorphic engineering (artificial brain), although I imagine this new research from the Karolinska Institute (Institutet) will be of some interest to that community. This research was done in the interest of developing* therapeutic interventions for brain diseases. One aspect of this news item/press release I find particularly interesting is the insistence that “no living parts” were used to create the artificial neuron,

A June 24, 2015 news item on ScienceDaily describes what the artificial neuron can do,

Scientists have managed to build a fully functional neuron by using organic bioelectronics. This artificial neuron contain [sic] no ‘living’ parts, but is capable of mimicking the function of a human nerve cell and communicate in the same way as our own neurons do. [emphasis mine]

A June 24, 2015 Karolinska Institute press release (also on EurekAlert), which originated the news item, describes how neurons communicate in the brain, standard techniques for stimulating neuronal cells, and the scientists’ work on a technique to improve stimulation,

Neurons are isolated from each other and communicate with the help of chemical signals, commonly called neurotransmitters or signal substances. Inside a neuron, these chemical signals are converted to an electrical action potential, which travels along the axon of the neuron until it reaches the end. Here at the synapse, the electrical signal is converted to the release of chemical signals, which via diffusion can relay the signal to the next nerve cell.

To date, the primary technique for neuronal stimulation in human cells is based on electrical stimulation. However, scientists at the Swedish Medical Nanoscience Centre (SMNC) at Karolinska Institutet in collaboration with collegues at Linköping University, have now created an organic bioelectronic device that is capable of receiving chemical signals, which it can then relay to human cells.

“Our artificial neuron is made of conductive polymers and it functions like a human neuron,” says lead investigator Agneta Richter-Dahlfors, professor of cellular microbiology. “The sensing component of the artificial neuron senses a change in chemical signals in one dish, and translates this into an electrical signal. This electrical signal is next translated into the release of the neurotransmitter acetylcholine in a second dish, whose effect on living human cells can be monitored.”

The research team hope that their innovation, presented in the journal Biosensors & Bioelectronics, will improve treatments for neurologial disorders which currently rely on traditional electrical stimulation. The new technique makes it possible to stimulate neurons based on specific chemical signals received from different parts of the body. In the future, this may help physicians to bypass damaged nerve cells and restore neural function.

“Next, we would like to miniaturize this device to enable implantation into the human body,” says Agneta Richer-Dahlfors. “We foresee that in the future, by adding the concept of wireless communication, the biosensor could be placed in one part of the body, and trigger release of neurotransmitters at distant locations. Using such auto-regulated sensing and delivery, or possibly a remote control, new and exciting opportunities for future research and treatment of neurological disorders can be envisaged.”

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

An organic electronic biomimetic neuron enables auto-regulated neuromodulation by Daniel T. Simon, Karin C. Larsson, David Nilsson, Gustav Burström, b, Dagmar Galter, Magnus Berggren, and Agneta Richter-Dahlfors. Biosensors and Bioelectronics Volume 71, 15 September 2015, Pages 359–364         doi:10.1016/j.bios.2015.04.058

This paper is behind a paywall.

As to anyone (other than myself) who may be curious about exactly what they used (other than “living parts”) to create an artificial neuron, there’s the paper’s abstract,

Current therapies for neurological disorders are based on traditional medication and electric stimulation. Here, we present an organic electronic biomimetic neuron, with the capacity to precisely intervene with the underlying malfunctioning signalling pathway using endogenous substances. The fundamental function of neurons, defined as chemical-to-electrical-to-chemical signal transduction, is achieved by connecting enzyme-based amperometric biosensors and organic electronic ion pumps. Selective biosensors transduce chemical signals into an electric current, which regulates electrophoretic delivery of chemical substances without necessitating liquid flow. Biosensors detected neurotransmitters in physiologically relevant ranges of 5–80 µM, showing linear response above 20 µm with approx. 0.1 nA/µM slope. When exceeding defined threshold concentrations, biosensor output signals, connected via custom hardware/software, activated local or distant neurotransmitter delivery from the organic electronic ion pump. Changes of 20 µM glutamate or acetylcholine triggered diffusive delivery of acetylcholine, which activated cells via receptor-mediated signalling. This was observed in real-time by single-cell ratiometric Ca2+ imaging. The results demonstrate the potential of the organic electronic biomimetic neuron in therapies involving long-range neuronal signalling by mimicking the function of projection neurons. Alternatively, conversion of glutamate-induced descending neuromuscular signals into acetylcholine-mediated muscular activation signals may be obtained, applicable for bridging injured sites and active prosthetics.

While it’s true neither are “living parts,” I believe both enzymes and organic electronic ion pumps can be found in biological organisms. The insistence on ‘nonliving’ in the press release suggests that scientists in Europe, if nowhere else, are still quite concerned about any hint that they are working on genetically modified organisms (GMO). It’s ironic when you consider that people blithely use enzyme-based cleaning and beauty products but one can appreciate the* scientists’ caution.

* ‘develop’ changed to ‘developing’ and ‘the’ added on July 3, 2015.