Category Archives: biomimcry

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.

Saharan silver ants: the nano of it all (science and technology)

Researchers at Columbia University (US) are on quite a publishing binge lately. The latest is a biomimicry story where researchers (from Columbia amongst other universities and including Brookhaven National Laboratory, which has issued its own news release) have taken a very close look at Saharan silver ants to determine how they stay cool in one of the hottest climates in the world. From a June 18, 2015 Columbia University news release (also on EurekAlert), Note: Links have been removed,

Nanfang Yu, assistant professor of applied physics at Columbia Engineering, and colleagues from the University of Zürich and the University of Washington, have discovered two key strategies that enable Saharan silver ants to stay cool in one of the hottest terrestrial environments on Earth. Yu’s team is the first to demonstrate that the ants use a coat of uniquely shaped hairs to control electromagnetic waves over an extremely broad range from the solar spectrum (visible and near-infrared) to the thermal radiation spectrum (mid-infrared), and that different physical mechanisms are used in different spectral bands to realize the same biological function of reducing body temperature. Their research, “Saharan silver ants keep cool by combining enhanced optical reflection and radiative heat dissipation,” is published June 18 [2015] in Science magazine.

The Columbia University news release expands on the theme,

“This is a telling example of how evolution has triggered the adaptation of physical attributes to accomplish a physiological task and ensure survival, in this case to prevent Saharan silver ants from getting overheated,” Yu says. “While there have been many studies of the physical optics of living systems in the ultraviolet and visible range of the spectrum, our understanding of the role of infrared light in their lives is much less advanced. Our study shows that light invisible to the human eye does not necessarily mean that it does not play a crucial role for living organisms.”

The project was initially triggered by wondering whether the ants’ conspicuous silvery coats were important in keeping them cool in blistering heat. Yu’s team found that the answer to this question was much broader once they realized the important role of infrared light. Their discovery that there is a biological solution to a thermoregulatory problem could lead to the development of novel flat optical components that exhibit optimal cooling properties.

“Such biologically inspired cooling surfaces will have high reflectivity in the solar spectrum and high radiative efficiency in the thermal radiation spectrum,” Yu explains. “So this may generate useful applications such as a cooling surface for vehicles, buildings, instruments, and even clothing.”

Saharan silver ants (Cataglyphis bombycina) forage in the Saharan Desert in the full midday sun when surface temperatures reach up to 70°C (158°F), and they must keep their body temperature below their critical thermal maximum of 53.6°C (128.48°F) most of the time. In their wide-ranging foraging journeys, the ants search for corpses of insects and other arthropods that have succumbed to the thermally harsh desert conditions, which they are able to endure more successfully. Being most active during the hottest moment of the day also allows these ants to avoid predatory desert lizards. Researchers have long wondered how these tiny insects (about 10 mm, or 3/8” long) can survive under such thermally extreme and stressful conditions.

Using electron microscopy and ion beam milling, Yu’s group discovered that the ants are covered on the top and sides of their bodies with a coating of uniquely shaped hairs with triangular cross-sections that keep them cool in two ways. These hairs are highly reflective under the visible and near-infrared light, i.e., in the region of maximal solar radiation (the ants run at a speed of up to 0.7 meters per second and look like droplets of mercury on the desert surface). The hairs are also highly emissive in the mid-infrared portion of the electromagnetic spectrum, where they serve as an antireflection layer that enhances the ants’ ability to offload excess heat via thermal radiation, which is emitted from the hot body of the ants to the cold sky. This passive cooling effect works under the full sun whenever the insects are exposed to the clear sky.

“To appreciate the effect of thermal radiation, think of the chilly feeling when you get out of bed in the morning,” says Yu. “Half of the energy loss at that moment is due to thermal radiation since your skin temperature is temporarily much higher than that of the surrounding environment.”

The researchers found that the enhanced reflectivity in the solar spectrum and enhanced thermal radiative efficiency have comparable contributions to reducing the body temperature of silver ants by 5 to 10 degrees compared to if the ants were without the hair cover. “The fact that these silver ants can manipulate electromagnetic waves over such a broad range of spectrum shows us just how complex the function of these seemingly simple biological organs of an insect can be,” observes Norman Nan Shi, lead author of the study and PhD student who works with Yu at Columbia Engineering.

Yu and Shi collaborated on the project with Rüdiger Wehner, professor at the Brain Research Institute, University of Zürich, Switzerland, and Gary Bernard, electrical engineering professor at the University of Washington, Seattle, who are renowned experts in the study of insect physiology and ecology. The Columbia Engineering team designed and conducted all experimental work, including optical and infrared microscopy and spectroscopy experiments, thermodynamic experiments, and computer simulation and modeling. They are currently working on adapting the engineering lessons learned from the study of Saharan silver ants to create flat optical components, or “metasurfaces,” that consist of a planar array of nanophotonic elements and provide designer optical and thermal radiative properties.

Yu and his team plan next to extend their research to other animals and organisms living in extreme environments, trying to learn the strategies these creatures have developed to cope with harsh environmental conditions.

“Animals have evolved diverse strategies to perceive and utilize electromagnetic waves: deep sea fish have eyes that enable them to maneuver and prey in dark waters, butterflies create colors from nanostructures in their wings, honey bees can see and respond to ultraviolet signals, and fireflies use flash communication systems,” Yu adds. “Organs evolved for perceiving or controlling electromagnetic waves often surpass analogous man-made devices in both sophistication and efficiency. Understanding and harnessing natural design concepts deepens our knowledge of complex biological systems and inspires ideas for creating novel technologies.”

Next, there’s the perspective provided by Brookhaven National Laboratory in a June 18, 2015 news item on Nanowerk (Note: It is very similar to the Columbia University news release but it takes a turn towards the technical challenges as you’ll see if you keep reading),

The paper, published by Columbia Engineering researchers and collaborators—including researchers from the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory—describes how the nanoscale structure of the hairs helps increase the reflectivity of the ant’s body in both visible and near-infrared wavelengths, allowing the insects to deflect solar radiation their bodies would otherwise absorb. The hairs also enhance emissivity in the mid-infrared spectrum, allowing heat to dissipate efficiently from the hot body of the ants to the cool, clear sky.

A June 18, 2015 BNL news release by Alasdair Wilkins, which originated the Nanowerk news item, describes the collaboration between the researchers and the special adjustments made to the equipment in service of this project (Note: A link has been removed),

In a typical experiment involving biological material such as nanoscale hairs, it would usually be sufficient to use an electron microscope to create an image of the surface of the specimen. This research, however, required Yu’s group to look inside the ant hairs and produce a cross-section of the structure’s interior. The relatively weak beam of electrons from a standard electron microscope would not be able to penetrate the surface of the sample.

The CFN’s dual beam system solves the problem by combining the imaging of an electron microscope with a much more powerful beam of gallium ions.  With 31 protons and 38 neutrons, each gallium ion is about 125,000 times more massive than an electron, and massive enough to create dents in the nanoscale structure – like throwing a stone against a wall. The researchers used these powerful beams to drill precise cuts into the hairs, revealing the crucial information hidden beneath the surface. Indeed, this particular application, in which the system was used to investigate a biological problem, was new for the team at CFN.

“Conventionally, this tool is used to produce cross-sections of microelectronic circuits,” said Camino. “The focused ion beam is like an etching tool. You can think of it like a milling tool in a machine shop, but at the nanoscale. It can remove material at specific places because you can see these locations with the SEM. So locally you remove material and you look at the under layers, because the cuts give you access to the cross section of whatever you want to look at.”

The ant hair research challenged the CFN team to come up with novel solutions to investigate the internal structures without damaging the more delicate biological samples.

“These hairs are very soft compared to, say, semiconductors or crystalline materials. And there’s a lot of local heat that can damage biological samples. So the parameters have to be carefully tuned not to do much damage to it,” he said. “We had to adapt our technique to find the right conditions.”

Another challenge lay in dealing with the so-called charging effect. When the dual beam system is trained on a non-conducting material, electrons can build up at the point where the beams hit the specimen, distorting the resulting image. The team at CFN was able to solve this problem by placing thin layers of gold over the biological material, making the sample just conductive enough to avoid the charging effect.

Revealing Reflectivity

While Camino’s team focused on helping Yu’s group investigate the structure of the ant hairs, Matthew Sfeir’s work with high-brightness Fourier transform optical spectroscopy helped to reveal how the reflectivity of the hairs helped Saharan silver ants regulate temperature. Sfeir’s spectrometer revealed precisely how much those biological structures reflect light across multiple wavelengths, including both visible and near-infrared light.

“It’s a multiplexed measurement,” Sfeir said, explaining his team’s spectrometer. “Instead of tuning through this wavelength and this wavelength, that wavelength, you do them all in one swoop to get all the spectral information in one shot. It gives you very fast measurements and very good resolution spectrally. Then we optimize it for very small samples. It’s a rather unique capability of CFN.”

Sfeir’s spectroscopy work draws on knowledge gained from his work at another key Brookhaven facility: the original National Synchrotron Light Source, where he did much of his postdoc work. His experience was particularly useful in analyzing the reflectivity of the biological structures across many different wavelengths of the electromagnetic spectrum.

“This technique was developed from my experience working with the infrared synchrotron beamlines,” said Sfeir. “Synchrotron beamlines are optimized for exactly this kind of thing. I thought, ‘Hey, wouldn’t it be great if we could develop a similar measurement for the type of solar devices we make at CFN?’ So we built a bench-top version to use here.”

Fascinating, non? At last, here’s a link to and a citation for the paper,

Keeping cool: Enhanced optical reflection and heat dissipation in silver ants by Norman Nan Shi, Cheng-Chia Tsai, Fernando Camino, Gary D. Bernard, Nanfang Yu, and Rüdiger Wehner. Science DOI: 10.1126/science.aab3564 Published online June 18, 2015

This paper is behind a paywall.

Discovering why your teeth aren’t perfectly crack-resistant

This helps make your teeth crack-resistant?

Caption: Illustration shows complex biostructure of dentin: the dental tubuli (yellow hollow cylinders, diameters appr. 1 micrometer) are surrounded by layers of mineralized collagen fibers (brown rods). The tiny mineral nanoparticles are embedded in the mesh of collagen fibers and not visible here. Credit: JB Forien @Charité

Caption: Illustration shows complex biostructure of dentin: the dental tubuli (yellow hollow cylinders, diameters appr. 1 micrometer) are surrounded by layers of mineralized collagen fibers (brown rods). The tiny mineral nanoparticles are embedded in the mesh of collagen fibers and not visible here. Credit: JB Forien @Charité

A June 10, 2015 Helmholtz Zentrum Berlin (HZB) press release (also on EurekAlert) explains how the illustration above relates to the research,

Human teeth have to serve for a lifetime, despite being subjected to huge forces. But the high failure resistance of dentin in teeth is not fully understood. An interdisciplinary team led by scientists of Charite Universitaetsmedizin Berlin has now analyzed the complex structure of dentin. At the synchrotron sources BESSY II at HZB, Berlin, Germany, and the European Synchrotron Radiation Facility ESRF, Grenoble, France, they could reveal that the mineral particles are precompressed.

The internal stress works against crack propagation and increases resistance of the biostructure.

Engineers use internal stresses to strengthen materials for specific technical purposes. Now it seems that evolution has long ‘known’ about this trick, and has put it to use in our natural teeth. Unlike bones, which are made partly of living cells, human teeth are not able to repair damage. Their bulk is made of dentin, a bonelike material consisting of mineral nanoparticles. These mineral nanoparticles are embedded in collagen protein fibres, with which they are tightly connected. In every tooth, such fibers can be found, and they lie in layers, making teeth tough and damage resistant. Still, it was not well understood, how crack propagation in teeth can be stopped.

The press release goes on to describe the new research and the teams which investigated the role of the mineral nanoparticles with regard to compression and cracking,

Now researchers from Charite Julius-Wolff-Institute, Berlin have been working with partners from Materials Engineering Department of Technische Universitaets Berlin, MPI of Colloids and Interfaces, Potsdam and Technion – Israel Institute of Technology, Haifa, to examine these biostructures more closely. They performed Micro-beam in-situ stress experiments in the mySpot BESSY facility of HZB, Berlin, Germany and analyzed the local orientation of the mineral nanoparticles using the nano-imaging facility of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France.

When the tiny collagen fibers shrink, the attached mineral particles become increasingly compressed, the science team found out. “Our group was able to use changes in humidity to demonstrate how stress appears in the mineral in the collagen fibers, Dr. Paul Zaslansky from Julius Wolff-Institute of Charite Berlin explains. “The compressed state helps to prevents cracks from developing and we found that compression takes place in such a way that cracks cannot easily reach the tooth inner parts, which could damage the sensitive pulp. In this manner, compression stress helps to prevent cracks from rushing through the tooth.

The scientists also examined what happens if the tight mineral-protein link is destroyed by heating: In that case, dentin in teeth becomes much weaker. We therefore believe that the balance of stresses between the particles and the protein is important for the extended survival of teeth in the mouth, Charite scientist Jean-Baptiste Forien says. Their results may explain why artificial tooth replacements usually do not work as well as healthy teeth do: they are simply too passive, lacking the mechanisms found in the natural tooth structures, and consequently fillings cannot sustain the stresses in the mouth as well as teeth do. “Our results might inspire the development of tougher ceramic structures for tooth repair or replacement, Zaslansky hopes.

Experiments took place as part of the DFG project “Biomimetic Materials Research: Functionality by Hierarchical Structuring of Materials (SPP1420).

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

Compressive Residual Strains in Mineral Nanoparticles as a Possible Origin of Enhanced Crack Resistance in Human Tooth Dentin by Jean-Baptiste Forien, Claudia Fleck, Peter Cloetens, Georg Duda, Peter Fratzl, Emil Zolotoyabko, and Paul Zaslansky. Nano Lett., 2015, 15 (6), pp 3729–3734 DOI: 10.1021/acs.nanolett.5b00143 Publication Date (Web): May 26, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

Synthesized spider silk from Montréal, Canada

On the heels of my May 29, 2015 post about synthesized spider silk at the Massachusetts Institute of Technology (MIT), researchers at the École Polytechnique de Montréal (Polytechnique Montreal) have also synthesized spider silk according to a June 3, 2015 news item on Nanowerk (Note: A link has been removed),

Professors Frederick Gosselin and Daniel Therriault, along with their master’s student Renaud Passieux, are not related to Spiderman. Nevertheless, these Polytechnique Montreal researchers have produced an ultra-tough polymer fibre directly inspired by spider silk! They recently published an article about the project in the journal Advanced Materials (“Instability-Assisted Direct Writing of Microstructured Fibers Featuring Sacrificial Bonds”).

A June 3, 2015 École Polytechnique de Montréal news release (also on EurekAlert), which originated the news item, further describes the achievement (at the microscale rather than the nanoscale),

Three to eight microns in diameter but five to ten times tougher than steel or Kevlar: despite its lightness, spider silk has such remarkable elongation and stretch-resistance properties that humans have long sought to replicate it, in order to make products with those same characteristics.

In large part, spider silk owes its exceptional strength – meaning its ability to absorb a large amount of energy before failing – to the particular molecular structure of the protein chain of which it’s composed. The mechanical origin of its strength drew the interest of researchers at the Laboratory for Multiscale Mechanics in Polytechnique Montréal’s Department of Mechanical Engineering.

“The silk protein coils upon itself like a spring. Each loop of the spring is attached to its neighbours with sacrificial bonds, chemical connections that break before the main molecular structural chain tears,” explained Professor Gosselin, who, along with his colleague Daniel Therriault, is co-supervising Renaud Passieux’s master’s research work. He added: “To break the protein by stretching it, you need to uncoil the spring and break each of the sacrificial bonds one by one, which takes a lot of energy. This is the mechanism we’re seeking to reproduce in laboratory,”

Imitating nature with polymer fibres

Their project involves making micrometric-sized microstructured fibres that have mechanical properties similar to those of spider silk. “It consists in pouring a filament of viscous polymeric solution toward a sub-layer that moves at a certain speed. So we create an instability,” said Renaud Passieux. “The filament forms a series of loops or coils, kind of like when you pour a thread of honey onto a piece of toast. [emphasis mine] Depending on the instability determined by the way the fluid runs, the fibre presents a particular geometry. It forms regular periodic patterns, which we call instability patterns.”

The fibre then solidifies as the solvent evaporates. Some instability patterns feature the formation of sacrificial bonds when the filament makes a loop and bonds to itself. At that point, it takes a pull with a strong energy output on the resulting fibre to succeed in breaking the sacrificial bonds, as they behave like protein-based spider silk.

“This project aims to understand how the instability used in making the substance influences the loops’ geometry and, as a result, the mechanical properties of the fibres we obtain,” explained Professor Therriault. “Our challenge is that the manufacturing process is multiphysical. It draws on concepts from numerous fields: fluid mechanics, microfabrication, strength of materials, polymer rheology and more.”

A vast range of applications for future tough fibre composites

These researchers think that one day, there will certainly be composites obtained by weaving together tough fibres of the type they’re currently developing. Such composites could, for example, make it possible to manufacture new safer and lighter casings for aircraft engines, which would prevent debris from dispersing in case of explosion. Many other applications can be foreseen, from surgical devices to bulletproof clothing to vehicle parts.

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

Instability-Assisted Direct Writing of Microstructured Fibers Featuring Sacrificial Bonds by Renaud Passieux, Leigh Guthrie, Somayeh Hosseini Rad, Martin Lévesque, Daniel Therriault, & Frédérick P. Gosselin. Advanced Materials  DOI: 10.1002/adma.201500603 First published: 15 May 2015

This paper is behind a paywall.

The researchers have also produced a video illustrating the ‘honey’ analogy as it relates to their work with spider silk,

Instability-Assisted Direct Writing of Micro-Structured Fibers featuring Sacrificial Bonds from Frederick P. Gosselin on Vimeo.

Synthesizing spider silk

Most of the research on spider silk and spider webs that’s featured here is usually from the Massachusetts Institute of Technology (MIT) and, more specifically, from professor Markus J. Buehler. This May 28, 2015 news item on ScienceDaily, which heralds the development of synthetic spider silk, is no exception,

After years of research decoding the complex structure and production of spider silk, researchers have now succeeded in producing samples of this exceptionally strong and resilient material in the laboratory. The new development could lead to a variety of biomedical materials — from sutures to scaffolding for organ replacements — made from synthesized silk with properties specifically tuned for their intended uses.

The findings are published this week in the journal Nature Communications by MIT professor of civil and environmental engineering (CEE) Markus Buehler, postdocs Shangchao Lin and Seunghwa Ryu, and others at MIT, Tufts University, Boston University, and in Germany, Italy, and the U.K.

The research, which involved a combination of simulations and experiments, paves the way for “creating new fibers with improved characteristics” beyond those of natural silk, says Buehler, who is also the department head in CEE. The work, he says, should make it possible to design fibers with specific characteristics of strength, elasticity, and toughness.

The new synthetic fibers’ proteins — the basic building blocks of the material — were created by genetically modifying bacteria to make the proteins normally produced by spiders. These proteins were then extruded through microfluidic channels designed to mimic the effect of an organ, called a spinneret, that spiders use to produce natural silk fibers.

A May 28, 2015 MIT news release (also on EurekAlert), which originated the news item, describes the work in more detail,

While spider silk has long been recognized as among the strongest known materials, spiders cannot practically be bred to produce harvestable fibers — so this new approach to producing a synthetic, yet spider-like, silk could make such strong and flexible fibers available for biomedical applications. By their nature, spider silks are fully biocompatible and can be used in the body without risk of adverse reactions; they are ultimately simply absorbed by the body.

The researchers’ “spinning” process, in which the constituent proteins dissolved in water are extruded through a tiny opening at a controlled rate, causes the molecules to line up in a way that produces strong fibers. The molecules themselves are a mixture of hydrophobic and hydrophilic compounds, blended so as to naturally align to form fibers much stronger than their constituent parts. “When you spin it, you create very strong bonds in one direction,” Buehler says.

The team found that getting the blend of proteins right was crucial. “We found out that when there was a high proportion of hydrophobic proteins, it would not spin any fibers, it would just make an ugly mass,” says Ryu, who worked on the project as a postdoc at MIT and is now an assistant professor at the Korea Advanced Institute of Science and Technology. “We had to find the right mix” in order to produce strong fibers, he says.

The researchers made use of computational modelling to speed up the process of synthesizing proteins for synthetic spider silk, from the news release,

This project represents the first use of simulations to understand silk production at the molecular level. “Simulation is critical,” Buehler explains: Actually synthesizing a protein can take several months; if that protein doesn’t turn out to have exactly the right properties, the process would have to start all over.

Using simulations makes it possible to “scan through a large range of proteins until we see changes in the fiber stiffness,” and then home in on those compounds, says Lin, who worked on the project as a postdoc at MIT and is now an assistant professor at Florida State University.

Controlling the properties directly could ultimately make it possible to create fibers that are even stronger than natural ones, because engineers can choose characteristics for a particular use. For example, while spiders may need elasticity so their webs can capture insects without breaking, those designing fibers for use as surgical sutures would need more strength and less stretchiness. “Silk doesn’t give us that choice,” Buehler says.

The processing of the material can be done at room temperature using water-based solutions, so scaling up manufacturing should be relatively easy, team members say. So far, the fibers they have made in the lab are not as strong as natural spider silk, but now that the basic process has been established, it should be possible to fine-tune the materials and improve its strength, they say.

“Our goal is to improve the strength, elasticity, and toughness of artificially spun fibers by borrowing bright ideas from nature,” Lin says. This study could inspire the development of new synthetic fibers — or any materials requiring enhanced properties, such as in electrical and thermal transport, in a certain direction.

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

Predictive modelling-based design and experiments for synthesis and spinning of bioinspired silk fibres by Shangchao Lin, Seunghwa Ryu, Olena Tokareva, Greta Gronau, Matthew M. Jacobsen, Wenwen Huang, Daniel J. Rizzo, David Li, Cristian Staii, Nicola M. Pugno, Joyce Y. Wong, David L. Kaplan, & Markus J. Buehler. Nature Communications 6, Article number: 6892 doi:10.1038/ncomms7892 Published 28 May 2015

This paper is behind a paywall.

My two most recent (before this one) postings about Buehler’s work are an August 5, 2014 piece about structural failures and a June 4, 2014 piece about spiderwebs and music.

Finally, I recognized one of the authors, Nicola Pugno from Italy. He’s been mentioned here more than once in regard to his biomimicry work which has often been focused on geckos and their adhesive qualities as per this April 3, 2014 post announcing his book ‘An Experimental Study on Adhesive or Anti-Adhesive, Bio-Inspired Experimental Nanomaterials‘ (co-authored with Emiliano Lepore).

Iridescent bird feathers inspire synthetic melanin for structural color/colour

I’m hoping one day they’ll be able to create textiles that rely on structure rather than pigment or dye for colour so my clothing will no longer fade with repeated washings and exposure to sunlight. There was one such textile, morphotex (named for the Blue Morpho butterfly, no longer produced by Japanese manufacturer Teijin but you can see a photo of the fabric which was fashioned into a dress by Australian designer Donna Sgro in my July 19, 2010 posting.

This particular project at the University of California at San Diego (UCSD), sadly, is not textile-oriented, but has resulted in a film according to a May 13, 2015 news item on ScienceDaily,

Inspired by the way iridescent bird feathers play with light, scientists have created thin films of material in a wide range of pure colors — from red to green — with hues determined by physical structure rather than pigments.

Structural color arises from the interaction of light with materials that have patterns on a minute scale, which bend and reflect light to amplify some wavelengths and dampen others. Melanosomes, tiny packets of melanin found in the feathers, skin and fur of many animals, can produce structural color when packed into solid layers, as they are in the feathers of some birds.

“We synthesized and assembled nanoparticles of a synthetic version of melanin to mimic the natural structures found in bird feathers,” said Nathan Gianneschi, a professor of chemistry and biochemistry at the University of California, San Diego. “We want to understand how nature uses materials like this, then to develop function that goes beyond what is possible in nature.”

A May 13, 2015 UCSD news release by Susan Brown (also on EurekAlert), which originated the news item, describes the inspiration and the work in more detail,

Gianneschi’s work focuses on nanoparticles that can sense and respond to the environment. He proposed the project after hearing Matthew Shawkey, a biology professor at the University of Akron, describe his work on the structural color in bird feathers at a conference. Gianneschi, Shawkey and colleagues at both universities report the fruits of the resulting collaboration in the journal ACS Nano, posted online May 12 [2015].

To mimic natural melanosomes, Yiwen Li, a postdoctoral fellow in Gianneschi’s lab, chemically linked a similar molecule, dopamine, into meshes. The linked, or polydopamine, balled up into spherical particles of near uniform size. Ming Xiao, a graduate student who works with Shawkey and polymer science professor Ali Dhinojwala at the University of Akron, dried different concentrations of the particles to form thin films of tightly packed polydopamine particles.

The films reflect pure colors of light; red, orange, yellow and green, with hue determined by the thickness of the polydopamine layer and how tightly the particles packed, which relates to their size, analysis by Shawkey’s group determined.

The colors are exceptionally uniform across the films, according to precise measurements by Dimitri Deheyn, a research scientist at UC San Diego’s Scripps Institution of Oceanography who studies how a wide variety of organisms use light and color to communicate. “This spatial mapping of spectra also tells you about color changes associated with changes in the size or depth of the particles,” Deheyn said.

The qualities of the material contribute to its potential application. Pure hue is a valuable trait in colorimetric sensors. And unlike pigment-based paints or dyes, structural color won’t fade. Polydopamine, like melanin, absorbs UV light, so coatings made from polydopamine could protect materials as well. Dopamine is also a biological molecule used to transmit information in our brains, for example, and therefore biodegradable.

“What has kept me fascinated for 15 years is the idea that one can generate colors across the rainbow through slight (nanometer scale) changes in structure,” said Shawkey whose interests range from the physical mechanisms that produce colors to how the structures grow in living organisms. “This idea of biomimicry can help solve practical problems but also enables us to test the mechanistic and developmental hypotheses we’ve proposed,” he said.

Natural melanosomes found in bird feathers vary in size and particularly shape, forming rods and spheres that can be solid or hollow. The next step is to vary the shapes of nanoparticles of polydopamine to mimic that variety to experimentally test how size and shape influence the particle’s interactions with light, and therefore the color of the material. Ultimately, the team hopes to generate a palette of biocompatible, structural color.

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

Bio-Inspired Structural Colors Produced via Self-Assembly of Synthetic Melanin Nanoparticles by Ming Xiao, Yiwen Li, Michael C. Allen, Dimitri D. Deheyn, Xiujun Yue, Jiuzhou Zhao, Nathan C. Gianneschi, Matthew D. Shawkey, and Ali Dhinojwala. ACS Nano, Article ASAP DOI: 10.1021/acsnano.5b01298 Publication Date (Web): May 4, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

For anyone who’d like to explore structural colour further, there’s this Feb. 7, 2013 posting which features excerpts from and a link to an excellent article by Cristina Luiggi for The Scientist.