Revolutionary self-sensing electric artificial muscles

Researchers from Queen Mary University of London have made groundbreaking advancements in bionics with the development of a new electric variable-stiffness artificial muscle. Published in Advanced Intelligent Systems, this innovative technology possesses self-sensing capabilities and has the potential to revolutionize soft robotics and medical applications. The artificial muscle seamlessly transitions between soft and hard states, while also sensing forces and deformations. With flexibility and stretchability similar to natural muscle, it can be integrated into intricate soft robotic systems and adapt to various shapes. By adjusting voltages, the muscle rapidly changes its stiffness and can monitor its own deformation through resistance changes. The fabrication process is simple and reliable, making it ideal for a range of applications, including aiding individuals with disabilities or patients in rehabilitation training.

In a study published recently in Advanced Intelligent Systems, researchers from Queen Mary University of London have made significant advancements in the field of bionics with the development of a new type of electric variable-stiffness artificial muscle that possesses self-sensing capabilities. This innovative technology has the potential to revolutionize soft robotics and medical applications.

Muscle contraction hardening is not only essential for enhancing strength but also enables rapid reactions in living organisms. Taking inspiration from nature, the team of researchers at QMUL's School of Engineering and Materials Science has successfully created an artificial muscle that seamlessly transitions between soft and hard states while also possessing the remarkable ability to sense forces and deformations.

Dr. Ketao Zhang, a Lecturer at Queen Mary and the lead researcher, explains the importance of variable stiffness technology in artificial muscle-like actuators. "Empowering robots, especially those made from flexible materials, with self-sensing capabilities is a pivotal step towards true bionic intelligence," says Dr. Zhang.

The cutting-edge artificial muscle developed by the researchers exhibits flexibility and stretchability similar to natural muscle, making it ideal for integration into intricate soft robotic systems and adapting to various geometric shapes. With the ability to withstand over 200% stretch along the length direction, this flexible actuator with a striped structure demonstrates exceptional durability.

By applying different voltages, the artificial muscle can rapidly adjust its stiffness, achieving continuous modulation with a stiffness change exceeding 30 times. Its voltage-driven nature provides a significant advantage in terms of response speed over other types of artificial muscles. Additionally, this novel technology can monitor its deformation through resistance changes, eliminating the need for additional sensor arrangements and simplifying control mechanisms while reducing costs.

The fabrication process for this self-sensing artificial muscle is simple and reliable. Carbon nanotubes are mixed with liquid silicone using ultrasonic dispersion technology and coated uniformly using a film applicator to create the thin layered cathode, which also serves as the sensing part of the artificial muscle. The anode is made directly using a soft metal mesh cut, and the actuation layer is sandwiched between the cathode and the anode. After the liquid materials cure, a complete self-sensing variable-stiffness artificial muscle is formed.

The potential applications of this flexible variable stiffness technology are vast, ranging from soft robotics to medical applications. The seamless integration with the human body opens up possibilities for aiding individuals with disabilities or patients in performing essential daily tasks. By integrating the self-sensing artificial muscle, wearable robotic devices can monitor a patient's activities and provide resistance by adjusting stiffness levels, facilitating muscle function restoration during rehabilitation training.

"While there are still challenges to be addressed before these medical robots can be deployed in clinical settings, this research represents a crucial stride towards human-machine integration," highlights Dr. Zhang. "It provides a blueprint for the future development of soft and wearable robots."

Read more at Science Daily

Mimicking an enigmatic property of circadian rhythms through an artificial chemical clock

Circadian rhythms are natural, internal oscillations that synchronize an organism's behaviors and physiological processes with their environment. These rhythms normally have a period of 24 hours and are regulated by internal chemical clocks that respond to cues from outside the body, such as light.

Although well studied in animals, plants, and bacteria, circadian rhythms all share an enigmatic property -- the oscillation period is not significantly affected by temperature, even though the rate of most biochemical reactions changes exponentially with temperature. This clearly indicates that some sort of temperature-compensation mechanism is at play. Interestingly, some scientists have managed to replicate such temperature-invariant qualities in certain oscillating chemical reactions. However, these reactions are often troublesome and require extremely precise adjustments on the reacting chemicals.

But what if there was a simpler way to achieve temperature compensation in an oscillating chemical reaction? In a recent study published in Scientific Reports, a team of researchers including Assistant Professor Yuhei Yamada of Tokyo Institute of Technology (Tokyo Tech), Japan, came up with a clever idea for a temperature compensation mechanism using a reaction called the Belousov-Zhabotinsky (BZ) oscillating reaction.

The key to their approach lies in soft, temperature-responsive gels made from poly(N-isopropylacrylamide), or 'PNIPAAm' for short, in which the BZ reaction can occur. These gels consist of polymeric strands that can accommodate a certain volume of solvent. However, because these gels shrink as temperature increases, the amount of solvent contained in the gel decreases as temperature rises.

The researchers exploited this property of PNIPAAm gels by adding ruthenium (Ru) sites on its constituent polymers. The periodic nature of the particular BZ reaction the researchers studied relies partially on the back-and-forth oxidation and reduction of ruthenium (Ru) ions. Thus, the speed of this reaction is affected by the relative concentrations of solvent and Ru. Because the PNIPAAm gels can accommodate less solvent when they shrink, the relative concentration of Ru in the gels increases with temperature.

As the research team demonstrated through experimental measurements and a thorough mathematical analysis, the abovementioned effects combine to form a temperature-compensation mechanism that renders the period of the BZ reaction unaffected by shifts in temperature. "The prepared BZ gels exhibited temperature compensability just like the circadian rhythms observed in living organisms," remarks Yamada.

Overall, this study demonstrates a completely new way to achieve temperature compensation in artificial biological clocks based on periodic reactions. Intriguingly, it's even possible that similar temperature-compensation mechanisms using temperature-responsive soft bodies exist in biological systems in nature, as Yamada explains: "Our study suggests that temperature compensation can be naturally self-sustainable through the output system of circadian machinery. This may explain why temperature compensation is a universal property of circadian rhythms seen in animals, plants, and bacteria, regardless of the molecular species involved."

Read more at Science Daily

Artificial neural networks learn better when they spend time not learning at all

Depending on age, humans need 7 to 13 hours of sleep per 24 hours. During this time, a lot happens: Heart rate, breathing and metabolism ebb and flow; hormone levels adjust; the body relaxes. Not so much in the brain.

"The brain is very busy when we sleep, repeating what we have learned during the day," said Maxim Bazhenov, PhD, professor of medicine and a sleep researcher at University of California San Diego School of Medicine. "Sleep helps reorganize memories and presents them in the most efficient way."

In previous published work, Bazhenov and colleagues have reported how sleep builds rational memory, the ability to remember arbitrary or indirect associations between objects, people or events, and protects against forgetting old memories.

Artificial neural networks leverage the architecture of the human brain to improve numerous technologies and systems, from basic science and medicine to finance and social media. In some ways, they have achieved superhuman performance, such as computational speed, but they fail in one key aspect: When artificial neural networks learn sequentially, new information overwrites previous information, a phenomenon called catastrophic forgetting.

"In contrast, the human brain learns continuously and incorporates new data into existing knowledge," said Bazhenov, "and it typically learns best when new training is interleaved with periods of sleep for memory consolidation."

Writing in the November 18, 2022 issue of PLOS Computational Biology, senior author Bazhenov and colleagues discuss how biological models may help mitigate the threat of catastrophic forgetting in artificial neural networks, boosting their utility across a spectrum of research interests.

The scientists used spiking neural networks that artificially mimic natural neural systems: Instead of information being communicated continuously, it is transmitted as discrete events (spikes) at certain time points.

They found that when the spiking networks were trained on a new task, but with occasional off-line periods that mimicked sleep, catastrophic forgetting was mitigated. Like the human brain, said the study authors, "sleep" for the networks allowed them to replay old memories without explicitly using old training data.

Memories are represented in the human brain by patterns of synaptic weight -- the strength or amplitude of a connection between two neurons.

"When we learn new information," said Bazhenov, "neurons fire in specific order and this increases synapses between them. During sleep, the spiking patterns learned during our awake state are repeated spontaneously. It's called reactivation or replay.

"Synaptic plasticity, the capacity to be altered or molded, is still in place during sleep and it can further enhance synaptic weight patterns that represent the memory, helping to prevent forgetting or to enable transfer of knowledge from old to new tasks."

When Bazhenov and colleagues applied this approach to artificial neural networks, they found that it helped the networks avoid catastrophic forgetting.

"It meant that these networks could learn continuously, like humans or animals. Understanding how human brain processes information during sleep can help to augment memory in human subjects. Augmenting sleep rhythms can lead to better memory.

"In other projects, we use computer models to develop optimal strategies to apply stimulation during sleep, such as auditory tones, that enhance sleep rhythms and improve learning. This may be particularly important when memory is non-optimal, such as when memory declines in aging or in some conditions like Alzheimer's disease."

Read more at Science Daily

How a soil microbe could rev up artificial photosynthesis

Plants rely on a process called carbon fixation -- turning carbon dioxide from the air into carbon-rich biomolecules - for their very existence. That's the whole point of photosynthesis, and a cornerstone of the vast interlocking system that cycles carbon through plants, animals, microbes and the atmosphere to sustain life on Earth.

But the carbon fixing champs are not plants, but soil bacteria. Some bacterial enzymes carry out a key step in carbon fixation 20 times faster than plant enzymes do, and figuring out how they do this could help scientists develop forms of artificial photosynthesis to convert the greenhouse gas into fuels, fertilizers, antibiotics and other products.

Now a team of researchers from the Department of Energy's SLAC National Accelerator Laboratory, Stanford University, Max Planck Institute for Terrestrial Microbiology in Germany, DOE's Joint Genome Institute (JGI) and the University of Concepción in Chile has discovered how a bacterial enzyme -- a molecular machine that facilitates chemical reactions -- revs up to perform this feat.

Rather than grabbing carbon dioxide molecules and attaching them to biomolecules one at a time, they found, this enzyme consists of pairs of molecules that work in sync, like the hands of a juggler who simultaneously tosses and catches balls, to get the job done faster. One member of each enzyme pair opens wide to catch a set of reaction ingredients while the other closes over its captured ingredients and carries out the carbon-fixing reaction; then, they switch roles in a continual cycle.

A single spot of molecular "glue" holds each pair of enzymatic hands together so they can alternate opening and closing in a coordinated way, the team discovered, while a twisting motion helps hustle ingredients and finished products in and out of the pockets where the reactions take place. When both glue and twist are present, the carbon-fixing reaction goes 100 times faster than without them.

"This bacterial enzyme is the most efficient carbon fixer that we know of, and we came up with a neat explanation of what it can do," said Soichi Wakatsuki, a professor at SLAC and Stanford and one of the senior leaders of the study, which was published in ACS Central Science this week.

"Some of the enzymes in this family act slowly but in a very specific way to produce just one product," he said. "Others are much faster and can craft chemical building blocks for all sorts of products. Now that we know the mechanism, we can engineer enzymes that combine the best features of both approaches and do a very fast job with all sorts of starting materials."

Improving on nature

The enzyme the team studied is part of a family called enoyl-CoA carboxylases/reductases, or ECRs. It comes from soil bacteria called Kitasatospora setae, which in addition to their carbon-fixing skills can also produce antibiotics.

Wakatsuki heard about this enzyme family half a dozen years ago from Tobias Erb of the Max Planck Institute for Terrestrial Microbiology in Germany and Yasuo Yoshikuni of JGI. Erb's research team had been working to develop bioreactors for artificial photosynthesis to convert carbon dioxide (CO2) from the atmosphere into all sorts of products.

As important as photosynthesis is to life on Earth, Erb said, it isn't very efficient. Like all things shaped by evolution over the eons, it's only as good as it needs to be, the result of slowly building on previous developments but never inventing something entirely new from scratch.

What's more, he said, the step in natural photosynthesis that fixes CO2 from the air, which relies on an enzyme called Rubisco, is a bottleneck that bogs the whole chain of photosynthetic reactions down. So using speedy ECR enzymes to carry out this step, and engineering them to go even faster, could bring a big boost in efficiency.

"We aren't trying to make a carbon copy of photosynthesis," Erb explained. "We want to design a process that's much more efficient by using our understanding of engineering to rebuild the concepts of nature. This 'photosynthesis 2.0' could take place in living or synthetic systems such as artificial chloroplasts -- droplets of water suspended in oil."

Portraits of an enzyme

Wakatsuki and his group had been investigating a related system, nitrogen fixation, which converts nitrogen gas from the atmosphere into compounds that living things need. Intrigued by the question of why ECR enzymes were so fast, he started collaborating with Erb's group to find answers.

Hasan DeMirci, a research associate in Wakatsuki's group who is now an assistant professor at Koc University and investigator with the Stanford PULSE Institute, led the effort at SLAC with help from half a dozen SLAC summer interns he supervised. "We train six or seven of them every year, and they were fearless," he said. "They came with open minds, ready to learn, and they did amazing things."

The SLAC team made samples of the ECR enzyme and crystallized them for examination with X-rays at the Advanced Photon Source at DOE's Argonne National Laboratory. The X-rays revealed the molecular structure of the enzyme -- the arrangement of its atomic scaffolding -- both on its own and when attached to a small helper molecule that facilitates its work.

Further X-ray studies at SLAC's Stanford Synchrotron Radiation Lightsource (SSRL) showed how the enzyme's structure shifted when it attached to a substrate, a kind of molecular workbench that assembles ingredients for the carbon fixing reaction and spurs the reaction along.

Finally, a team of researchers from SLAC's Linac Coherent Light Source (LCLS) carried out more detailed studies of the enzyme and its substrate at Japan's SACLA X-ray free-electron laser. The choice of an X-ray laser was important because it allowed them to study the enzyme's behavior at room temperature -- closer to its natural environment -- with almost no radiation damage.

Meanwhile, Erb's group in Germany and Associate Professor Esteban Vo?hringer-Martinez's group at the University of Concepción in Chile carried out detailed biochemical studies and extensive dynamic simulations to make sense of the structural data collected by Wakatsuki and his team.

The simulations revealed that the opening and closing of the enzyme's two parts don't just involve molecular glue, but also twisting motions around the central axis of each enzyme pair, Wakatsuki said.

"This twist is almost like a rachet that can push a finished product out or pull a new set of ingredients into the pocket where the reaction takes place," he said. Together, the twisting and synchronization of the enzyme pairs allow them to fix carbon 100 times a second.

The ECR enzyme family also includes a more versatile branch that can interact with many different kinds of biomolecules to produce a variety of products. But since they aren't held together by molecular glue, they can't coordinate their movements and therefore operate much more slowly.

"If we can increase the rate of those sophisticated reactions to make new biomolecules," Wakatsuki said, "that would be a significant jump in the field."

From static shots to fluid movies

So far the experiments have produced static snapshots of the enzyme, the reaction ingredients and the final products in various configurations.

"Our dream experiment," Wakatsuki said, "would be to combine all the ingredients as they flow into the path of the X-ray laser beam so we could watch the reaction take place in real time."

The team actually tried that at SACLA, he said, but it didn't work. "The CO2 molecules are really small, and they move so fast that it's hard to catch the moment when they attach to the substrate," he said. "Plus the X-ray laser beam is so strong that we couldn't keep the ingredients in it long enough for the reaction to take place. When we pressed hard to do this, we managed to break the crystals."

An upcoming high-energy upgrade to LCLS will likely solve that problem, he added, with pulses that arrive much more frequently -- a million times per second -- and can be individually adjusted to the ideal strength for each sample.

Read more at Science Daily

Complex three-dimensional kidney tissue generated in the lab from the scratch

A research team based in Kumamoto University (Japan) has created complex 3D kidney tissue in the lab solely from cultured mouse embryonic stem (ES) cells. These organoids could lead the way to better kidney research and, eventually, artificial kidneys for human transplant.

By focusing on an often-overlooked tissue type of organoid generation research, a type of organ tissue made up of various support and connective tissues called the stroma, Dr. Ryuichi Nishinakamura and his team were able to generate the last of a three-part puzzle that they had been working on for several years. Once the three pieces were combined, the resulting structure was found to be kidney-like in its architecture. The researchers believe that their work will be used to advance kidney research and even lead to a transplantable organ in the future.

The kidney is a very important organ for continued good health because it acts as a filter to extract waste and excess water from blood. It is a complex organ that develops from the combination of three components. Protocols have already been established by various research teams, including Dr. Nishinakamura's team at the Institute of Molecular Embryology and Genetics (IMEG) at Kumamoto University, to induce two of the components (the nephron progenitor and the ureteric bud) from mouse ES cells.

In this, their most recent work, the IMEG team has developed a method to induce the third and final component, kidney-specific stromal progenitor, in mice. Furthermore, by combining these three components in vitro, the researchers were able to generate a kidney-like 3D tissue, consisting of extensively branched tubules and several other kidney-specific structures.

The researchers believe that this is the first ever report on the in-lab generation of such a complex kidney structure from scratch. The IMEG team has already succeeded in inducing the first two components from human iPS cells. If this last component can also be generated from human cells, a similarly complex human kidney should be achievable.

Read more at Science Daily

Artificial muscles made of proteins

Dr. Stefan Schiller and Dr. Matthias Huber from the University of Freiburg's livMatS Cluster of Excellence have succeeded in developing a muscle solely on the basis of natural proteins. The autonomous contractions of the material, which the researchers presented in the journal Advanced Intelligent Systems, can be controlled with the help of pH and temperature changes. The movements are driven by a chemical reaction that consumes molecular energy for this purpose. "Our artificial muscle is still a prototype," says Schiller. "However, the high biocompatibility of the material and the possibility of adjusting its composition to match particular tissue could pave the way for future applications in reconstructive medicine, prosthetics, pharmaceutics, or soft robotics."

In the past, scientists have already taken natural proteins as a basis for developing artificial muscle systems and built them into miniscule molecular machines or into polymers. However, it has not yet been possible to develop synthetic muscle materials that are entirely bio-based and move autonomously with the help of chemical energy.

Material based on the natural protein elastin

The material used by the Freiburg team is based on elastin, a natural fibrous protein that also occurs in humans, for instance giving elasticity to the skin and blood vessels. Following the model of this protein, the researchers developed two elastin-like proteins, one of which responds, for example, to fluctuations in pH, the other to changes in temperature. The scientists combined the two proteins by means of photochemical cross-linking to form a bilayered material. It is possible in this process to flexibly shape the material and set the direction of its movement.

Contractions can be switched on and off with the help of temperature changes

The researchers succeeded in inducing the rhythmic contractions by using a chemical energy source as fuel, in this case sodium sulfite. In an oscillating chemical reaction in which the pH changes in cycles due to a special linkage of several reactions, the added energy was converted into mechanical energy via non-equilibrium states of the material. In this way, the researchers induced the material to contract autonomously in a cyclical manner. They were also able to switch the contractions on and off with the help of temperature changes: The oscillating chemical reaction started at a temperature of around 20 degrees Celsius, and the material began to make rhythmic movements. In the process, it was possible to program certain states for the material to assume and to reset them again with another stimulus. The scientists thus achieved a simple system for implementing learning and forgetting at the material level.

Read more at Science Daily

Mechanical engineers develop new high-performance artificial muscle technology

In the field of robotics, researchers are continually looking for the fastest, strongest, most efficient and lowest-cost ways to actuate, or enable, robots to make the movements needed to carry out their intended functions.

The quest for new and better actuation technologies and 'soft' robotics is often based on principles of biomimetics, in which machine components are designed to mimic the movement of human muscles -- and ideally, to outperform them. Despite the performance of actuators like electric motors and hydraulic pistons, their rigid form limits how they can be deployed. As robots transition to more biological forms and as people ask for more biomimetic prostheses, actuators need to evolve.

Associate professor (and alum) Michael Shafer and professor Heidi Feigenbaum of Northern Arizona University's Department of Mechanical Engineering, along with graduate student researcher Diego Higueras-Ruiz, published a paper in Science Robotics presenting a new, high-performance artificial muscle technology they developed in NAU's Dynamic Active Systems Laboratory. The paper, titled "Cavatappi artificial muscles from drawing, twisting, and coiling polymer tubes," details how the new technology enables more human-like motion due to its flexibility and adaptability, but outperforms human skeletal muscle in several metrics.

"We call these new linear actuators cavatappi artificial muscles based on their resemblance to the Italian pasta," Shafer said.

Because of their coiled, or helical, structure, the actuators can generate more power, making them an ideal technology for bioengineering and robotics applications. In the team's initial work, they demonstrated that cavatappi artificial muscles exhibit specific work and power metrics ten and five times higher than human skeletal muscles, respectively, and as they continue development, they expect to produce even higher levels of performance.

"The cavatappi artificial muscles are based on twisted polymer actuators (TPAs), which were pretty revolutionary when they first came out because they were powerful, lightweight and cheap. But they were very inefficient and slow to actuate because you had to heat and cool them. Additionally, their efficiency is only about two percent," Shafer said. "For the cavatappi, we get around this by using pressurized fluid to actuate, so we think these devices are far more likely to be adopted. These devices respond about as fast as we can pump the fluid. The big advantage is their efficiency. We have demonstrated contractile efficiency of up to about 45 percent, which is a very high number in the field of soft actuation."

The engineers think this technology could be used in soft robotics applications, conventional robotic actuators (for example, for walking robots), or even potentially in assistive technologies like exoskeletons or prostheses.

"We expect that future work will include the use of cavatappi artificial muscles in many applications due to their simplicity, low-cost, lightweight, flexibility, efficiency and strain energy recovery properties, among other benefits," Shafer said.

Technology is available for licensing, partnering opportunities.

Working with the NAU Innovations team, the inventors have taken steps to protect their intellectual property. The technology has entered the protection and early commercialization stage and is available for licensing and partnering opportunities. For more information, please contact NAU Innovations.

Read more at Science Daily

Silk fibers improve bioink for 3D-printed artificial tissues and organs

 How do you test, in early-stage research, whether a potential pharmaceutical effectively targets a human tumor, organ, or some other part of the body? How do you grow a new hand or some other body part? Researchers are in the early stages of using 3D cell printing technology to make developments like these happen. A standard way -- currently unavailable -- to fix the cells in place after printing would help researchers avoid having to 'reinvent the wheel' in every new investigation.

In a study recently published in Materials Today Bio, researchers from Osaka University have used silk nanofibers obtained by mechanical disintegration to enhance the printing process without damaging the cells or cell assemblies. An attractive point of silk for this application is that silk is believed to be a safe material for humans. This development will help bring 3D cell printing research out of the laboratory and into real-world biomedical use.

To obtain the fibers, the researchers started with virgin silk, then removed the protein sericin from it because this protein causes inflammation in patients. Next, the researchers ground the remaining biocompatible material into nanofibers. The fibers can be sterilized -- without damaging them -- for medical use, with common laboratory equipment.

"Our silk fibers are excellent additives to bioink cell printing media," says lead author Shinji Sakai. "They are compatible with many media, such as those containing gelatin, chitosan, or hyaluronic acid, giving them a broad range of potential applications."

The main purpose of the fibers was to ensure that the cells in the bioink retained their 3D positioning after printing without damaging the cells. The fibers fulfill this purpose by enhancing the integrity of the bioink and minimizing the damaging high mechanical stresses often placed on cells during printing.

"Various mechanical experiments say the same thing: the nanofibers enhanced the properties of the printing media," explains Professor Sakai. "For example, Young's modulus -- a measure of stiffness -- increased several-fold and remained enhanced for over a month."

The fibers help printed configurations retain their structural integrity after printing. For example, a nose-shaped configuration retained its shape only when printed with bioink containing the silk fibers. Over 85% of the cells in the bioink remained alive after a week in the printed bioink with or without the added fibers, indicating that adding the fibers did not damage the cells.

Read more at Science Daily

'Artificial leaf' successfully produces clean gas

A widely-used gas that is currently produced from fossil fuels can instead be made by an 'artificial leaf' that uses only sunlight, carbon dioxide and water, and which could eventually be used to develop a sustainable liquid fuel alternative to petrol.

The carbon-neutral device sets a new benchmark in the field of solar fuels, after researchers at the University of Cambridge demonstrated that it can directly produce the gas -- called syngas -- in a sustainable and simple way.

Rather than running on fossil fuels, the artificial leaf is powered by sunlight, although it still works efficiently on cloudy and overcast days. And unlike the current industrial processes for producing syngas, the leaf does not release any additional carbon dioxide into the atmosphere. The results are reported in the journal Nature Materials.

Syngas is currently made from a mixture of hydrogen and carbon monoxide, and is used to produce a range of commodities, such as fuels, pharmaceuticals, plastics and fertilisers.

"You may not have heard of syngas itself but every day, you consume products that were created using it. Being able to produce it sustainably would be a critical step in closing the global carbon cycle and establishing a sustainable chemical and fuel industry," said senior author Professor Erwin Reisner from Cambridge's Department of Chemistry, who has spent seven years working towards this goal.

The device Reisner and his colleagues produced is inspired by photosynthesis -- the natural process by which plants use the energy from sunlight to turn carbon dioxide into food.

On the artificial leaf, two light absorbers, similar to the molecules in plants that harvest sunlight, are combined with a catalyst made from the naturally abundant element cobalt.

When the device is immersed in water, one light absorber uses the catalyst to produce oxygen. The other carries out the chemical reaction that reduces carbon dioxide and water into carbon monoxide and hydrogen, forming the syngas mixture.

As an added bonus, the researchers discovered that their light absorbers work even under the low levels of sunlight on a rainy or overcast day.

"This means you are not limited to using this technology just in warm countries, or only operating the process during the summer months," said PhD student Virgil Andrei, first author of the paper. "You could use it from dawn until dusk, anywhere in the world."

The research was carried out in the Christian Doppler Laboratory for Sustainable SynGas Chemistry in the University's Department of Chemistry. It was co-funded by the Austrian government and the Austrian petrochemical company OMV, which is looking for ways to make its business more sustainable.

"OMV has been an avid supporter of the Christian Doppler Laboratory for the past seven years. The team's fundamental research to produce syngas as the basis for liquid fuel in a carbon neutral way is ground-breaking," said Michael-Dieter Ulbrich, Senior Advisor at OMV.

Other 'artificial leaf' devices have also been developed, but these usually only produce hydrogen. The Cambridge researchers say the reason they have been able to make theirs produce syngas sustainably is thanks the combination of materials and catalysts they used.

These include state-of-the-art perovskite light absorbers, which provide a high photovoltage and electrical current to power the chemical reaction by which carbon dioxide is reduced to carbon monoxide, in comparison to light absorbers made from silicon or dye-sensitised materials. The researchers also used cobalt as their molecular catalyst, instead of platinum or silver. Cobalt is not only lower-cost, but it is better at producing carbon monoxide than other catalysts.

The team is now looking at ways to use their technology to produce a sustainable liquid fuel alternative to petrol.

Syngas is already used as a building block in the production of liquid fuels. "What we'd like to do next, instead of first making syngas and then converting it into liquid fuel, is to make the liquid fuel in one step from carbon dioxide and water," said Reisner, who is also a Fellow of St John's College.

Although great advances are being made in generating electricity from renewable energy sources such as wind power and photovoltaics, Reisner says the development of synthetic petrol is vital, as electricity can currently only satisfy about 25% of our total global energy demand. "There is a major demand for liquid fuels to power heavy transport, shipping and aviation sustainably," he said.

Read more at Science Daily

Artificial photosynthesis transforms carbon dioxide into liquefiable fuels

Carbon dioxide molecules illustration.

Chemists at the University of Illinois have successfully produced fuels using water, carbon dioxide and visible light through artificial photosynthesis. By converting carbon dioxide into more complex molecules like propane, green energy technology is now one step closer to using excess CO2 to store solar energy -- in the form of chemical bonds -- for use when the sun is not shining and in times of peak demand.

Plants use sunlight to drive chemical reactions between water and CO2 to create and store solar energy in the form of energy-dense glucose. In the new study, the researchers developed an artificial process that uses the same green light portion of the visible light spectrum used by plants during natural photosynthesis to convert CO2 and water into fuel, in conjunction with electron-rich gold nanoparticles that serve as a catalyst. The new findings are published in the journal Nature Communications.

"The goal here is to produce complex, liquefiable hydrocarbons from excess CO2 and other sustainable resources such as sunlight," said Prashant Jain, a chemistry professor and co-author of the study. "Liquid fuels are ideal because they are easier, safer and more economical to transport than gas and, because they are made from long-chain molecules, contain more bonds -- meaning they pack energy more densely."

In Jain's lab, Sungju Yu, a postdoctoral researcher and first author of the study, uses metal catalysts to absorb green light and transfer electrons and protons needed for chemical reactions between CO2 and water -- filling the role of the pigment chlorophyll in natural photosynthesis.

Gold nanoparticles work particularly well as a catalyst, Jain said, because their surfaces interact favorably with the CO2 molecules, are efficient at absorbing light and do not break down or degrade like other metals that can tarnish easily.

There are several ways in which the energy stored in bonds of the hydrocarbon fuel is freed. However, the easy conventional method of combustion ends up producing more CO2 -- which is counterproductive to the notion of harvesting and storing solar energy in the first place, Jain said.

"There are other, more unconventional potential uses from the hydrocarbons created from this process," he said. "They could be used to power fuel cells for producing electrical current and voltage. There are labs across the world trying to figure out how the hydrocarbon-to-electricity conversion can be conducted efficiently," Jain said.

As exciting as the development of this CO2-to-liquid fuel may be for green energy technology, the researchers acknowledge that Jain's artificial photosynthesis process is nowhere near as efficient as it is in plants.

Read more at Science Daily

Scientist constructs artificial photosynthetic cells

These are schematics of the artificial photosynthetic cell encapsulating artificial organelle consists of ATP synthase and bacteriorhodopsin. The artificial organelle synthesizes ATP by light illumination. The photosynthesized ATP was consumed for transcription, GTP synthesis, or translation.

A team led by associate professor Yutetsu Kuruma of the Earth-Life Science Institute (ELSI) at Tokyo Institute of Technology has constructed simple artificial cells that can produce chemical energy that helps synthesize parts of the cells themselves. This work marks an important milestone in constructing fully photosynthetic artificial cells, and may shed light on how primordial cells used sunlight as an energy source early in life's history.

Scientists build artificial cells as models of primitive cells, as well as to understand how modern cells function. Many sub-cellular systems have now been built by simply mixing cell components together. However, real living cells construct and organize their own components. It has also been a long time goal of research to build artificial cells that can also synthesize their own constituents using the energy available in the environment.

The Tokyo Tech team combined a cell-free protein synthesis system, which consisted of various biological macromolecules harvested from living cells, and small protein-lipids aggregates called proteoliposomes, which contained the proteins ATP synthase and bacteriorhodopsin, also purified from living cells, inside giant synthetic vesicles. ATP synthase is a biological protein complex that uses the potential energy difference between the liquid inside a cell and the liquid in the cell's environment to make the molecule adenosine triphosphate (ATP), which is the energy currency of the cell. Bacteriorhodopsin is a light-harvesting protein from primitive microbes that uses light energy to transport hydrogen ions outside of the cell, thus generating a potential energy difference to help ATP synthase operate. Thus, these artificial cells would be able to use light to make a hydrogen ion gradient that would help make the fuel cells use to run their sub-cellular systems, including making more protein.

Just as the scientists hoped, the photosynthesized ATP was consumed as a substrate for transcription, the process by which biology makes messenger RNA (mRNA) from DNA, and as an energy for translation, the process by which biology makes protein from mRNA. By also including the genes for parts of the ATP synthase and the light-harvesting bacteriorhodopsin, these processes also eventually drive the synthesis of more bacteriorhodopsin and the constituent proteins of ATP synthase, a few copies of which were included to "jump-start" the proteoliposome. The newly formed bacteriorhodopsin and ATP synthase parts then spontaneously integrated into the artificial photosynthetic organelles and further enhanced ATP photosynthesis activity.

As professor Kuruma states "I have been trying for a long time to construct a living artificial cell, especially focusing on membranes. In this work, our artificial cells were wrapped in lipid membranes, and small membrane structures were encapsulated inside them. In this way, the cell membrane is the most important aspect of forming a cell, and I wanted to show the importance of this point in the study of artificial cell and feedback in origins of life studies."

Kuruma thinks the most impact point of this work is that artificial cells can produce energy to synthesize the parts of the cell itself. This means that the artificial cells could be made to be energetically independent and then it would be possible to construct self-sustaining cells, just like actual biological ones cells. "The most challenging thing in this work was the photosynthesis of the bacteriorhodopsin and the ATP synthase parts, which are membrane proteins. We tried to photosynthesize a full ATP synthase, which has 8 kinds of component proteins, but we could not because of the low productivity of the cell-free protein synthesis system. But, if it was upgraded, we may photosynthesize the whole 8 kinds component proteins."

Read more at Science Daily

Moving artificial leaves out of the lab and into the air

An artificial, bio-inspired leaf. Carbon dioxide (red and black balls) enter the leaf as water (white and red balls) evaporates from the bottom of the leaf. An artificial photosystem (purple circle at the center of the leaf) made of a light absorber coated with catalysts converts carbon dioxide to carbon monoxide and converts water to oxygen (shown as double red balls) using sunlight.

Artificial leaves mimic photosynthesis -- the process whereby plants use water and carbon dioxide from the air to produce carbohydrates using energy from the sun. But even state-of-the-art artificial leaves, which hold promise in reducing carbon dioxide from the atmosphere, only work in the laboratory because they use pure, pressurized carbon dioxide from tanks.

But now, researchers from the University of Illinois at Chicago have proposed a design solution that could bring artificial leaves out of the lab and into the environment. Their improved leaf, which would use carbon dioxide -- a potent greenhouse gas -- from the air, would be at least 10 times more efficient than natural leaves at converting carbon dioxide to fuel. Their findings are reported in the journal ACS Sustainable Chemistry & Engineering.

"So far, all designs for artificial leaves that have been tested in the lab use carbon dioxide from pressurized tanks. In order to implement successfully in the real world, these devices need to be able to draw carbon dioxide from much more dilute sources, such as air and flue gas, which is the gas given off by coal-burning power plants," said Meenesh Singh, assistant professor of chemical engineering in the UIC College of Engineering and corresponding author on the paper.

Unhooking the pressurized carbon dioxide supply from these leaves means that they must have a way to collect and concentrate carbon dioxide from the air to drive their artificial photosynthetic reactions.

Singh and his colleague Aditya Prajapati, a graduate student in his lab, proposed solving this problem by encapsulating a traditional artificial leaf inside a transparent capsule made of a semi-permeable membrane of quaternary ammonium resin and filled with water. The membrane allows water from inside to evaporate out when warmed by sunlight. As water passes out through the membrane, it selectively pulls in carbon dioxide from the air. The artificial photosynthetic unit inside the capsule is made up of a light absorber coated with catalysts that convert the carbon dioxide to carbon monoxide, which can be siphoned off and used as a basis for the creation of various synthetic fuels. Oxygen is also produced and can either be collected or released into the surrounding environment.

"By enveloping traditional artificial leaf technology inside this specialized membrane, the whole unit is able to function outside, like a natural leaf," Singh said.

According to their calculations, 360 leaves, each 1.7 meters long and 0.2 meters wide, would produce close to a half-ton of carbon monoxide per day that could be used as the basis for synthetic fuels. Three hundred and sixty of these artificial leaves covering a 500-meter square area would be able to reduce carbon dioxide levels by 10 percent in the surrounding air within 100 meters of the array in one day.

Read more at Science Daily

Artificial intelligence for studying the ancient human populations of Patagonia

Technological landscapes of nautical mobility (red circles, with some blues that are less well classified by the algorithm) and pedestrian mobility (orange and purple circles) in hunter-gatherer groups that lived in the extreme south of South America.

Argentine and Spanish researchers have used statistical techniques of automatic learning to analyze mobility patterns and technology of the hunter-gatherer groups that inhabited the Southern Cone of America, from the time they arrived about 12,000 years ago until the end of the 19th century. Big data from archaeological sites located in the extreme south of Patagonia have been used for this study.

The presence of humans on the American continent dates back to at least 14,500 years ago, according to datings made at archaeological sites such as Monte Verde, in Chile's Los Lagos Region. But the first settlers continued moving towards the southernmost confines of America.

Now, researchers from Argentina's National Council for Scientific and Technical Research (CONICET) and two Spanish institutions (the Spanish National Research Council and the University of Burgos) have analyzed the relationships between mobility and technology developed by those societies that originated in the far south of Patagonia.

The study, published in the Royal Society Open Science journal, is based on an extensive database of all available archaeological evidence of human presence in this region, from the time the first groups arrived in the early Holocene (12,000 years ago) until the end of the 19th century.

This was followed by the application of machine learning techniques, a statistical system that allows the computer to learn from many data (in this case, big data from characteristic technological elements of the sites) in order to carry out classifications and predictions.

"It is by means of automatic classification algorithms that we have identified two technological packages or 'landscapes': one that characterizes pedestrian hunter-gatherer groups (with their own stone and bone tools) and the other characterizing those that had nautical technology, such as canoes, harpoons and mollusc shells used to make beads," explains Ivan Briz i Godino, an archaeologist of the National Council for Scientific and Technical Research (CONICET) of Argentina and co-author of the work.

"In future excavations, when sets of technological elements such as those we have detected appear, we'll be able to directly deduce the type of mobility of the group or the connections with other communities," adds Briz.

The results of the study have also made it possible to obtain maps with the settlements of the two communities, and this, in turn, has made it possible to locate large regions in which they interacted and shared their technological knowledge. In the case of groups with nautical technology, it has been confirmed that they arrived at around the beginning of the Mid-Holocene (some 6,000 years ago) from the channels and islands of the South Pacific, moving along the coast of what is now Chile.

Read more at Science Daily

Artificial Photoreceptors Restore Sight in Blind Mice

An estimated 39 million people worldwide are blind, and another 245 million suffer from moderately or extremely impaired vision.

Retinal diseases like macular degeneration and retinitis pigmentosa slowly rob people of their sight as the rods and cones in the retina gradually atrophy and fail. One of the only hopes for averting total blindness in those cases is to receive a “bionic eye,” a wireless retinal implant that receives electrical signals from a video camera worn on a pair of sunglasses.

These bionic devices, while potentially life-changing for people with total vision loss, have some limitations: They can only be implanted in one eye, they require patients to wear a power source and processor at all times, and even the best cases report a very low visual acuity of 20/1200 with no color recognition and few perceptible details.

Now a team of Chinese researchers believes it has developed a new type of retinal prosthesis that restores full-color vision without any external power or processors. The implant replaces the malfunctioning layer of rods and cones with artificial photoreceptors made from gold-titania nanowires, according to a paper in Nature Communications.

The retina is a thin membrane on the back of the eye that converts incoming light into electrical signals that are then processed by the brain. The retina is only half a millimeter thick, but contains three distinct cellular layers. The bottom layer, farthest from the light source, holds the rods and cones, also known as photoreceptor cells. It’s the photoreceptor layer that’s compromised in people with retinal diseases.

The top layer of the retina is formed by glial cells, a type of neuron or nerve cell typically found in the brain. It’s the glial cells that capture the electrical impulses from the photoreceptors and channel them through the optic nerve to be processed by the brain into images.

Back in the 1980s, scientists discovered that they could bypass the photoreceptor layer entirely and send electrical impulses directly to the glial cells. Since glial cells are usually unaffected in patients with macular degeneration and retinitis pigmentosa, researchers started looking for ways to replace the faulty photoreceptor layer with implanted electrodes.

The Argus II Retinal Prosthesis System developed by California-based Second Sight is the current state-of-the-art solution. An external video camera worn on a pair of sunglasses captures images that are sent to a small video-processing unit carried by the patient. The images are translated into electrical signals that are transmitted wirelessly to an electrode array implanted in the back of the eye. The implant broadcasts the electrical signals to the glial cells, which carry them to the brain.

The Argus II is marketed as a “humanitarian device,” not a cure for blindness. With lots of training, patients slowly learn to interpret what they’re seeing — flashes of contrasting light and blurry shapes — as familiar faces and objects. But the idea of the implant was never to recover full vision.

The Chinese approach seems to offer new hope for people with congenital or degenerative retinal diseases. The idea is to replace the retina’s biological photoreceptors with artificial cells that carry the same innate ability to convert light into electricity.

Jiayi Zhang and Gengfeng Zheng at Fudan University in Shanghai developed semiconducting nanowires of titania flecked with gold nanoparticles that replicate the retina’s real photoreceptors in both form and function. In an email, Zhang told Seeker that the nanowires have a pillar structure like rods and cones, and can convert light into electricity without the need of an outside power source.

The Chinese research team used the pillar-like nanowires to make a tiny photodiode array that could be implanted directly into the retina of blind mice. To test if the implant successfully restored vision, they implanted a second electrode array in each mouse’s visual cortex to record the electrical signals transmitted from the eye’s glial cells.

Five months post-surgery, wrote Zhang, the mice with nanowire retinal implants produced responses in the visual cortex that were similar to wild-type mice with no history of retinal disease.

Read more at Seeker

Virtual predator is 'self-aware', behaves like living counterpart

Cyberslug was modeled on Pleurobranchaea californica, a sea slug with a simple nervous system.

Scientists report in the journal eNeuro that they've built an artificially intelligent ocean predator that behaves a lot like the original flesh-and-blood organism on which it was modeled. The virtual creature, "Cyberslug," reacts to food and responds to members of its own kind much like the actual animal, the sea slug Pleurobranchaea californica, does.

Unlike most other AI entities, Cyberslug has a simple self-awareness, said University of Illinois molecular and integrative physiology professor Rhanor Gillette, who led the work with software engineer Mikhail Voloshin.

"That is, it relates its motivation and memories to its perception of the external world, and it reacts to information on the basis of how that information makes it feel," Gillette said.

Cyberslug knows when it's hungry, for example. It also has learned which other kinds of virtual sea slugs are yummy to eat and which are less desirable.

Sea slugs typically choose one of three responses when encountering another creature in the wild, Gillette said. "Do I eat it? Do I mate with it? Or do I flee?"

To make the right choice, they must be able sense their own internal state (Am I hungry?), get cues from their environment (How does it smell?) and remember past encounters (Did this thing sting me last time?).

"Their default response is avoidance, but hunger, sensation and learning together form their 'appetitive state,' and if that is high enough the sea slug will attack," Gillette said.

"When P. californica is super hungry, it will even attack a painful stimulus," he said. "And when the animal is not hungry, it usually will avoid even an appetitive stimulus. This is a cost-benefit decision." Cyberslug behaves the same way.

In previous work, Gillette and his colleagues worked out the brain circuitry that allows sea slugs to operate in the wild, "down to individual neurons," he said. To test the accuracy of their models, the researchers experimented with simple computer simulations. One of the first circuitry boards Voloshin built to represent the sea slug brain was housed in a plastic foam food takeout container.

The new model uses more sophisticated algorithms to simulate Cyberslug's competing goals and decision-making, Gillette said. Over time it learns what is good -- and not so good -- to bite. Just like P. californica, the more it eats, the more satiated it becomes and the more likely it is to avoid other creatures. But as hunger returns, Cyberslug becomes a less picky eater.

Read more at Science Daily

Metalens combined with an artificial muscle

This is a photo of the metalens (made of silicon) mounted on a transparent, stretchy polymer film, without any electrodes. The colorful iridescence is produced by the large number of nanostructures within the metalens.

Inspired by the human eye, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed an adaptive metalens, that is essentially a flat, electronically controlled artificial eye. The adaptive metalens simultaneously controls for three of the major contributors to blurry images: focus, astigmatism, and image shift.

The research is published in Science Advances.

"This research combines breakthroughs in artificial muscle technology with metalens technology to create a tunable metalens that can change its focus in real time, just like the human eye," said Alan She, a graduate student at SEAS and first author of the paper. "We go one step further to build the capability of dynamically correcting for aberrations such as astigmatism and image shift, which the human eye cannot naturally do."

"This demonstrates the feasibility of embedded optical zoom and autofocus for a wide range of applications including cell phone cameras, eyeglasses and virtual and augmented reality hardware," said Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS and senior author of the paper. "It also shows the possibility of future optical microscopes, which operate fully electronically and can correct many aberrations simultaneously."

The Harvard Office of Technology Development has protected the intellectual property relating to this project and is exploring commercialization opportunities.

To build the artificial eye, the researchers first needed to scale-up the metalens.

Prior metalenses were about the size of a single piece of glitter. They focus light and eliminate spherical aberrations through a dense pattern of nanostructures, each smaller than a wavelength of light.

"Because the nanostructures are so small, the density of information in each lens is incredibly high," said She. "If you go from a 100 micron-sized lens to a centimeter sized lens, you will have increased the information required to describe the lens by ten thousand. Whenever we tried to scale-up the lens, the file size of the design alone would balloon up to gigabytes or even terabytes."

To solve this problem, the researchers developed a new algorithm to shrink the file size to make the metalens compatible with the technology currently used to fabricate integrated circuits. In a paper recently published in Optics Express, the researchers demonstrated the design and fabrication of metalenses up to centimeters or more in diameter.

"This research provides the possibility of unifying two industries: semiconductor manufacturing and lens-making, whereby the same technology used to make computer chips will be used to make metasurface-based optical components, such as lenses," said Capasso.

Next, the researchers needed to adhere the large metalens to an artificial muscle without compromising its ability to focus light. In the human eye, the lens is surrounded by ciliary muscle, which stretches or compresses the lens, changing its shape to adjust its focal length. Capasso and his team collaborated with David Clarke, Extended Tarr Family Professor of Materials at SEAS and a pioneer in the field of engineering applications of dielectric elastomer actuators, also known as artificial muscles.

The researchers chose a thin, transparent dielectic elastomer with low loss -- meaning light travels through the material with little scattering -- to attach to the lens. To do so, they needed to developed a platform to transfer and adhere the lens to the soft surface.

"Elastomers are so different in almost every way from semiconductors that the challenge has been how to marry their attributes to create a novel multi-functional device and, especially how to devise a manufacturing route," said Clarke. "As someone who worked on one of the first scanning electron microscopes (SEMs) in the mid 1960's, it is exhilarating to be a part of creating an optical microscope with the capabilities of an SEM, such as real-time aberration control."

The elastomer is controlled by applying voltage. As it stretches, the position of nanopillars on the surface of the lens shift. The metalens can be tuned by controlling both the position of the pillars in relation to their neighbors and the total displacement of the structures. The researchers also demonstrated that the lens can simultaneously focus, control aberrations caused by astigmatisms, as well as perform image shift.

Together, the lens and muscle are only 30 microns thick.

"All optical systems with multiple components -- from cameras to microscopes and telescopes -- have slight misalignments or mechanical stresses on their components, depending on the way they were built and their current environment, that will always cause small amounts of astigmatism and other aberrations, which could be corrected by an adaptive optical element," said She. "Because the adaptive metalens is flat, you can correct those aberrations and integrate different optical capabilities onto a single plane of control."

Next, the researchers aim to further improve the functionality of the lens and decrease the voltage required to control it.

Read more at Science Daily

Artificial muscles power up with new gel-based robotics

(a) Overview of wearing set-up of the assist wear. (b) Structure of the multilayered PVC gel actuator with two types of anode mesh electrodes. The red layer with small holes is comprised of slide electrodes to minimize the friction with the slide shafts. (c) Contraction and expansion movement of the stretching type actuator with the DC field turned on and off. (d) FlexiForce sensor-based motion detection (position estimator). (e) Power and controller.

Scientists are one step closer to artificial muscles. Orthotics have come a long way since their initial wood and strap designs, yet innovation lapsed when it came to compensating for muscle power -- until now.

A collaborative research team has designed a wearable robot to support a person's hip joint while walking. The team, led by Minoru Hashimoto, a professor of textile science and technology at Shinshu University in Japan, published the details of their prototype in Smart Materials and Structures, a journal published by the Institute of Physics.

"With a rapidly aging society, an increasing number of elderly people require care after suffering from stroke, and other-age related disabilities. Various technologies, devices, and robots are emerging to aid caretakers," wrote Hashimoto, noting that several technologies meant to assist a person with walking are often cumbersome to the user. "[In our] current study, [we] sought to develop a lightweight, soft, wearable assist wear for supporting activities of daily life for older people with weakened muscles and those with mobility issues."

The wearable system consists of plasticized polyvinyl chloride (PVC) gel, mesh electrodes, and applied voltage. The mesh electrodes sandwich the gel, and when voltage is applied, the gel flexes and contracts, like a muscle. It's a wearable actuator, the mechanism that causes movement.

"We thought that the electrical mechanical properties of the PVC gel could be used for robotic artificial muscles, so we started researching the PVC gel," said Hashimoto. "The ability to add voltage to PVC gel is especially attractive for high speed movement, and the gel moves with high speed with just a few hundred volts."

In a preliminary evaluation, a stroke patient with some paralysis on one side of his body walked with and without the wearable system.

"We found that the assist wear enabled natural movement, increasing step length and decreasing muscular activity during straight line walking," wrote Hashimoto. The researchers also found that adjusting the charge could change the level of assistance the actuator provides.

The robotic system earned first place in demonstrations with their multilayer PVC gel artificial muscle at the, "24th International Symposium on Smart Structures and Materials & Nondestructive Evaluation and Health Monitoring" for SPIE the international society for optics and photonics.

Read more at Science Daily

Scientists watch 'artificial atoms' assemble into perfect lattices with many uses

An illustration shows nanocrystals assembling into an ordered ‘superlattice’ – a process that a SLAC/Stanford team was able to observe in real time with X-rays from the Stanford Synchrotron Radiation Lightsource (SSRL). They discovered that this assembly takes just a few seconds when carried out in hot solutions. The results open the door for rapid self-assembly of nanocrystal building blocks into complex structures with applications in optoelectronics, solar cells, catalysis and magnetic materials.

Some of the world's tiniest crystals are known as "artificial atoms" because they can organize themselves into structures that look like molecules, including "superlattices" that are potential building blocks for novel materials.

Now scientists from the Department of Energy's SLAC National Accelerator Laboratory and Stanford University have made the first observation of these nanocrystals rapidly forming superlattices while they are themselves still growing. What they learn will help scientists fine-tune the assembly process and adapt it to make new types of materials for things like magnetic storage, solar cells, optoelectronics and catalysts that speed chemical reactions.

The key to making it work was the serendipitous discovery that superlattices can form superfast -- in seconds rather than the usual hours or days -- during the routine synthesis of nanocrystals. The scientists used a powerful beam of X-rays at SLAC's Stanford Synchrotron Radiation Lightsource (SSRL) to observe the growth of nanocrystals and the rapid formation of superlattices in real time.

A paper describing the research, which was done in collaboration with scientists at the DOE's Argonne National Laboratory, was published today in Nature.

"The idea is to see if we can get an independent understanding of how these superlattices grow so we can make them more uniform and control their properties," said Chris Tassone, a staff scientist at SSRL who led the study with Matteo Cargnello, assistant professor of chemical engineering at Stanford

Tiny Crystals with Outsized Properties

Scientists have been making nanocrystals in the lab since the 1980s. Because of their tiny size -they're billionths of a meter wide and contain just 100 to 10,000 atoms apiece -- they are governed by the laws of quantum mechanics, and this gives them interesting properties that can be changed by varying their size, shape and composition. For instance, spherical nanocrystals known as quantum dots, which are made of semiconducting materials, glow in colors that depend on their size; they are used in biological imaging and most recently in high-definition TV displays.

In the early 1990s, researchers started using nanocrystals to build superlattices, which have the ordered structure of regular crystals, but with small particles in place of individual atoms. These, too, are expected to have unusual properties that are more than the sum of their parts.

But until now, superlattices have been grown slowly at low temperatures, sometimes in a matter of days.

That changed in February 2016, when Stanford postdoctoral researcher Liheng Wu serendipitously discovered that the process can occur much faster than scientists had thought.

'Something Weird Is Happening'

He was trying to make nanocrystals of palladium -- a silvery metal that's used to promote chemical reactions in catalytic converters and many industrial processes -- by heating a solution containing palladium atoms to more than 230 degrees Celsius. The goal was to understand how these tiny particles form, so their size and other properties could be more easily adjusted.

The team added small windows to a reaction chamber about the size of a tangerine so they could shine an SSRL X-ray beam through it and watch what was happening in real time.

"It's kind of like cooking," Cargnello explained. "The reaction chamber is like a pan. We add a solvent, which is like the frying oil; the main ingredients for the nanocrystals, such as palladium; and condiments, which in this case are surfactant compounds that tune the reaction conditions so you can control the size and composition of the particles. Once you add everything to the pan, you heat it up and fry your stuff."

Wu and Stanford graduate student Joshua Willis expected to see the characteristic pattern made by X-rays scattering off the tiny particles.They saw a completely different pattern instead.

"So something weird is happening," they texted their advisor.

The something weird was that the palladium nanocrystals were assembling into superlattices.

A Balance of Forces

At this point, "The challenge was to understand what brings the particles together and attracts them to each other but not too strongly, so they have room to wiggle around and settle into an ordered position," said Jian Qin, an assistant professor of chemical engineering at Stanford who performed theoretical calculations to better understand the self-assembly process.

Once the nanocrystals form, what seems to be happening is that they acquire a sort of hairy coating of surfactant molecules. The nanocrystals glom together, attracted by weak forces between their cores, and then a finely tuned balance of attractive and repulsive forces between the dangling surfactant molecules holds them in just the right configuration for the superlattice to grow.

To the scientists' surprise, the individual nanocrystals then kept on growing, along with the superlattices, until all the chemical ingredients in the solution were used up, and this unexpected added growth made the material swell. The researchers said they think this occurs in a wide range of nanocrystal systems, but had never been seen because there was no way to observe it in real time before the team's experiments at SSRL.

Read more at Science Daily