How to Predict Stress at Atomic Scale

The amount of stress a material can withstand before it cracks is critical information when designing aircraft, spacecraft, and other structures. Aerospace engineers at the University of Illinois Urbana-Champaign used machine learning for the first time to predict stress in copper at the atomic scale.

According to Huck Beng Chew and his doctoral student Yue Cui, materials, such as copper, are very different at these very small scales.

Left: Machine learning based on artificial neural networks as constitutive laws for atomic stress predictions. Right: Quantifying the local stress state of grain boundaries from atomic coordinate information

Metals are typically polycrystalline in that they contain many grains,” Chew said. “Each grain is a single crystal structure where all the atoms are arranged neatly and very orderly.  But the atomic structure of the boundary where these grains meet can be very complex and tend to have very high stresses.”

These grain boundary stresses are responsible for the fracture and fatigue properties of the metal, but until now, such detailed atomic-scale stress measurements were confined to molecular dynamics simulation models. Using data-driven approaches based on machine learning enables the study to quantify, for the first time, the grain boundary stresses in actual metal specimens imaged by electron microscopy.

“We used molecular dynamics simulations of copper grain boundaries to train our machine learning algorithm to recognize the arrangements of the atoms along the boundaries and identify patterns in the stress distributions within different grain boundary structures,” Cui said. Eventually, the algorithm was able to predict very accurately the grain boundary stresses from both simulation and experimental image data with atomic-level resolution.

We tested the accuracy of the machine learning algorithm with lots of different grain boundary structures until we were confident that the approach was reliable,” Cui explained. The task was more challenging than they imagined, and they had to include physics-based constraints in their algorithms to achieve accurate predictions with limited training data.

When you train the machine learning algorithm on specific grain boundaries, you will get extremely high accuracy in the stress predictions of these same boundaries,” Chew said, “but the more important question is, can the algorithm then predict the stress state of a new boundary that it has never seen before?” For Chew , the answer is yes, and very well in fact.

Source: https://aerospace.illinois.edu/

How To Create a Spectrum of Natural-looking Hair Colors

We’ve long been warned of the risks of dyeing hair at home and in salons. Products used can cause allergies and skin irritation — an estimated one percent of people have an allergy to dye. Furthermore, repeated use of some dyes has been linked to cancer. But there soon may be a solution for the growing list of salons and hair color enthusiasts searching for natural alternatives to dyes and cosmetics.

Northwestern University researchers have developed a new way to create a spectrum of natural-looking hair colors, ranging from blond to black, by using enzymes to catalyze synthetic melaninMelanin is an enigmatic and ubiquitous material often found in the form of brown or black pigment. Northwestern’s Nathan Gianneschi, the research lead and associate director for the International Institute for Nanotechnology, said every type of organism produces melanin, making it a readily available and versatile material to use in the lab.

Synthetic melanin can create colors ranging from blond to black

In humans, it’s in the back of our eye to help with vision, it’s in our skin to help with protecting skin cells from UV damage,” Gianneschi said. “But birds also use it as a spectacular color display — peacock feathers are made of melanin entirely.”

Gianneschi is Professor of Chemistry in Northwestern’s Weinberg College of Arts and Sciences and a professor of materials science and engineering and biomedical engineering in Northwestern Engineering. Claudia Battistella, a postdoctoral fellow in Gianneschi’s lab, is the paper’s first author.

The research was published in the journal Chemistry of Materials.

Source: https://www.mccormick.northwestern.edu/

Nanostructured rubber-like material could replace human tissue

Researchers from Chalmers University of Technology, Sweden, have created a new, rubber-like material with a unique set of properties, which could act as a replacement for human tissue in medical procedures. The material has the potential to make a big difference to many people’s lives.

​In the development of medical technology products, there is a great demand for new naturalistic materials suitable for integration with the body. Introducing materials into the body comes with many risks, such as serious infections, among other things. Many of the substances used today, such as Botox, are very toxic. There is a need for new, more adaptable materials. In the new study, the Chalmers researchers developed a material consisting solely of components that have already been shown to work well in the body.

The foundation of the material is the same as plexiglass, a material which is common in medical technology applications. Through redesigning its makeup, and through a process called nanostructuring, they gave the newly patented material a unique combination of properties. The researchers’ initial intention was to produce a hard bone-like material, but they were met with surprising results.

Chalmers researchers have developed a new material that could be suitable for various medical applications. The 3D printed ‘nose’ above, for example, shows how the material could act as a possible replacement for cartilage.​
We were really surprised that the material turned to be very soft, flexible and extremely elastic. It would not work as a bone replacement material, we concluded. But the new and unexpected properties made our discovery just as exciting,” says Anand Kumar Rajasekharan, PhD in Materials Science and one of the researchers behind the study.
The results showed that the new rubber-like material may be appropriate for many applications which require an uncommon combination of properties high elasticity, easy processability, and suitability for medical uses.

The first application we are looking at now is urinary catheters. The material can be constructed in such a way that prevents bacteria from growing on the surface, meaning it is very well suited for medical uses,” says Martin Andersson, research leader for the study and Professor of Chemistry at Chalmers.

The structure of the new nano-rubber material allows its surface to be treated so that it becomes antibacterial, in a natural, non-toxic way. This is achieved by sticking antimicrobial peptides – small proteins which are part of our innate immune system – onto its surface. This can help reduce the need for antibiotics, an important contribution to the fight against growing antibiotic resistance.
Because the new material can be injected and inserted via keyhole surgery, it can also help reduce the need for drastic surgery and operations to rebuild parts of the body. The material can be injected via a standard cannula as a viscous fluid, so that it forms its own elastic structures within the body. Or, the material can also be 3D printed into specific structures as required.
There are many diseases where the cartilage breaks down and friction results between bones, causing great pain for the affected person. This material could potentially act as a replacement in those cases,” Martin Andersson continues.
A further advantage of the material is that it contains three-dimensionally ordered nanopores. This means it can be loaded with medicine, for various therapeutic purposes such as improving healing and reducing inflammation. This allows for localised treatment, avoiding, for example, having to treat the entire body with drugs, something that could help reduce problems associated with side effects. Since it is non-toxic, it also works well as a filler – the researchers see plastic surgery therefore as another very interesting potential area of application for the new material.

The research was recently published in the scientific journal ACS Nano.

Source: https://www.chalmers.se/

3-D printing of tissue-like vascular structures

An international team of scientists have discovered a new material that can be 3-D printed to create tissue-like vascular structures. In a new study published today in Nature Communications, led by Professor Alvaro Mata at the University of Nottingham and Queen Mary University London, researchers have developed a way to 3-D print graphene oxide with a protein which can organise into tubular structures that replicate some properties of vascular tissue.

Cross-section of a bioprinted tubular structure with endothelial cells (green) on and embedded within the wall

This work offers opportunities in biofabrication by enabling simulatenous top-down 3-D bioprinting and bottom-up of synthetic and biological components in an orderly manner from the nanoscale. Here, we are biofabricating micro-scale capillary-like fluidic structures that are compatible with cells, exhibit physiologically relevant properties, and have the capacity to withstand flow. This could enable the recreation of vasculature in the lab and have implications in the development of safer and more efficient drugs, meaning treatments could potentially reach patients much more quickly,”said Professor Mata.

Self-assembly is the process by which multiple components can organise into larger well-defined structures. Biological systems rely on this process to controllably assemble molecular building-blocks into complex and functional materials exhibiting remarkable properties such as the capacity to grow, replicate, and perform robust functions.

The new biomaterial is made by the self-assembly of a protein with graphene oxide. The mechanism of assembly enables the flexible (disordered) regions of the protein to order and conform to the graphene oxide, generating a strong interaction between them. By controlling the way in which the two components are mixed, it is possible to guide their assembly at multiple size scales in the presence of cells and into complex robust structures.

The material can then be used as a 3-D printing bioink to print structures with intricate geometries and resolutions down to 10 um. The research team have demonstrated the capacity to build vascular-like structures in the presence of cells and exhibiting biologically relevant chemical and .

 “There is a great interest to develop materials and fabrication processes that emulate those from nature. However, the ability to build robust functional materials and devices through the self-assembly of molecular components has until now been limited. This research introduces a new method to integrate proteins with  by self-assembly in a way that can be easily integrated with additive manufacturing to easily fabricate biofluidic devices that allow us replicate key parts of human tissues and organs in the lab,” explained  Dr. Yuanhao Wu, the lead researcher on the project.

Source: https://phys.org/
AND
https://www.nature.com/

Flexible Generators Turn Movement Into Energy

Wearable devices that harvest energy from movement are not a new idea, but a material created at Rice University may make them more practical. The Rice lab of chemist James Tour has adapted laser-induced graphene (LIG) into small, metal-free devices that generate electricity. Like rubbing a balloon on hair, putting LIG composites in contact with other surfaces produces static electricity that can be used to power devices. For that, thank the triboelectric effect, by which materials gather a charge through contact. When they are put together and then pulled apart, surface charges build up that can be m.

In experiments, the researchers connected a folded strip of LIG to a string of light-emitting diodes and found that tapping the strip produced enough energy to make them flash. A larger piece of LIG embedded within a flip-flop let a wearer generate energy with every step, as the graphene composite’s repeated contact with skin produced a current to charge a small capacitor.

An electron microscope image shows a cross-section of a laser-induced graphene and polyimide composite created at Rice University for use as a triboelectric nanogenerator. The devices are able to turn movement into energy that can then be stored for later use

This could be a way to recharge small devices just by using the excess energy of heel strikes during walking, or swinging arm movements against the torso,” Tour said.

LIG is a graphene foam produced when chemicals are heated on the surface of a polymer or other material with a laser, leaving only interconnected flakes of two-dimensional carbon. The lab first made LIG on common polyimide, but extended the technique to plants, food, treated paper and wood.

The project is detailed in the American Chemical Society journal ACS Nano.

Source: http://news.rice.edu/

How To Extend The Charge-to-charge Life of Phones And Electric Cars By 40 %

The need to store energy for portable devices, vehicles and housing is ever increasing.The transformation from fossil fuels to renewable energy sources need to be hastened to decrease greenhouse gases and limit global warming. The utilization of wind and solar power requires effective storage system to ensure continuous energy supply as a part of smart grid. Li-ion batteries are considered to be the best route for many advanced storage applications related to the clean electricity due to their high energy density.

The latest lithium-ion batteries on the market are likely to extend the charge-to-charge life of phones and electric cars by as much as 40 percent. This leap forward, which comes after more than a decade of incremental improvements, is happening because developers replaced the battery’s graphite anode with one made from silicon. Research from Drexel University and Trinity College in Ireland now suggests that an even greater improvement could be in line if the silicon is fortified with a special type of material called MXene.

Regarding the present Li-ion batteries, one of the limiting factors in their performance is the anode material that most commonly is graphite. Silicon is a promising material for Li-ion battery anodes: By using silicon instead of graphite, the energy density of a battery cell ccould be increased by 30 %. To achieve this, several obstacles have to be overcome: First, silicon experiences a volume expansion of 300 % when lithiated. During discharging, the particles tend to fracture and lose contact. Secondly, the volume expansion prevents the formation of a stable electrode-electrolyte interface resulting in a continuous decomposition of the electrolyte. These two reasons are main causes for the limited use of silicon in commercial batteries.

The image shows PSi microparticles connected to each other with CNTs to improve the conductivity of the material

Both of the above mentioned problems with silicon material can be avoided by designing optimal porous structures of mesoporous silicon (PSi). Porosity of PSi needs to be high enough for the material to be able to withstand the volume expansion but also low enough so that the volumetric capacity/energy density is still better than for graphite anodes.

Source: https://www.nature.com/

Self-Healing Coating Protects Metals From Corrosion

It’s hard to believe that a tiny crack could take down a gigantic metal structure. But sometimes bridges collapse, pipelines rupture and fuselages detach from airplanes due to hard-to-detect corrosion in tiny cracks, scratches and dents. A Northwestern University team has developed a new coating strategy for metal that self-heals within seconds when scratched, scraped or cracked. The novel material could prevent these tiny defects from turning into localized corrosion, which can cause major structures to fail.

CLICK ON THE IMAGE TO ENJOY THE VIDEO

Localized corrosion is extremely dangerous,” said Jiaxing Huang, who led the research. “It is hard to prevent, hard to predict and hard to detect, but it can lead to catastrophic failure.” Huang is a professor of materials science and engineering in Northwestern’s McCormick School of Engineering.

When damaged by scratches and cracks, Huang’s patent-pending system readily flows and reconnects to rapidly heal right before the eyes. The researchers demonstrated that the material can heal repeatedly — even after scratching the exact same spot nearly 200 times in a row.While a few self-healing coatings already exist, those systems typically work for nanometer- to micron-sized damages. To develop a coating that can heal larger scratches in the millimeter-scale, Huang and his team looked to fluid. “When a boat cuts through water, the water goes right back together,” Huang said. “The ‘cut’ quickly heals because water flows readily. We were inspired to realize that fluids, such as oils, are the ultimate self-healing system.” But common oils flows too readily, Huang noted. So he and his team needed to develop a system with contradicting properties: fluidic enough to flow automatically but not so fluidic that it drips off the metal’s surface.

The team met the challenge by creating a network of lightweight particles — in this case graphene capsules — to thicken the oil. The network fixes the oil coating, keeping it from dripping. But when the network is damaged by a crack or scratch, it releases the oil to flow readily and reconnect. Huang said the material can be made with any hollow, lightweight particlenot just graphene. “The particles essentially immobilize the oil film,” Huang said. “So it stays in place.”

The study was published  in Research, the first Science Partner Journal recently launched by the American Association for the Advancement of Science (AAAS) in collaboration with the China Association for Science and Technology (CAST).

Source: https://news.northwestern.edu/

Ultrathin, Ultralight NanoCardboard For Aerospace

When choosing materials to make something, trade-offs need to be made between a host of properties, such as thickness, stiffness and weight. Depending on the application in question, finding just the right balance is the difference between success and failure. Now, a team of Penn Engineers has demonstrated a new material they call “nanocardboard,” an ultrathin equivalent of corrugated paper cardboard. A square centimeter of nanocardboard weighs less than a thousandth of a gram and can spring back into shape after being bent in half.

Nanocardboard is made out of an aluminum oxide film with a thickness of tens of nanometers, forming a hollow plate with a height of tens of microns. Its , similar to that of corrugated cardboard, makes it more than ten thousand times as stiff as a solid plate of the same mass.

CLICK ON THE IMAGE TO ENJOY THE VIDEO

Nanocardboard is made out of an aluminum oxide film with a thickness of tens of nanometers, forming a hollow plate with a height of tens of microns. Its sandwich structure, similar to that of corrugated cardboard, makes it more than ten thousand times as stiff as a solid plate of the same mass. A square centimeter of nanocardboard weighs less than a thousandth of a gram and can spring back into shape after being bent in half.

Nanocardboard‘s stiffness-to-weight ratio makes it ideal for aerospace and microrobotic applications, where every gram counts. In addition to unprecedented mechanical properties, nanocardboard is a supreme thermal insulator, as it mostly consists of empty space. Future work will explore an intriguing phenomenon that results from a combination of properties: shining a light on a piece of nanocardboard allows it to levitate. Heat from the light creates a difference in temperatures between the two sides of the plate, which pushes a current of air molecules out through the bottom.

Igor Bargatin, Assistant Professor of Mechanical Engineering, along with lab members Chen Lin and Samuel Nicaise, led the study.

They published their results in the journal Nature Communications.

Source: https://phys.org/