The system is remarkably simple, based on a three-layered material that can be applied or even sprayed onto the surfaces to be treated. It collects solar radiation, converts it to heat, and spreads that heat around so that the melting is not just confined to the areas exposed directly to the sunlight. And, once applied, it requires no further action or power source. It can even do its de-icing work at night, using artificial lighting.

The new system is described today in the journal Science Advances, in a paper by MIT associate professor of mechanical engineering Kripa Varanasi and postdocs Susmita Dash and Jolet de Ruiter.

“Icing is a major problem for aircraft, for wind turbines, powerlines, offshore oil platforms, and many other places,” Varanasi says. “The conventional ways of getting around it are de-icing sprays or by heating, but those have issues.”

Inspired by the sun

The usual de-icing sprays for aircraft and other applications use ethylene glycol, a chemical that is environmentally unfriendly. Airlines don’t like to use active heating, both for cost and safety reasons. Varanasi and other researchers have investigated the use of superhydrophobic surfaces to prevent icing passively, but those coatings can be impaired by frost formation, which tends to fill the microscopic textures that give the surface its ice-shedding properties.

As an alternate line of inquiry, Varanasi and his team considered the energy given off by the sun. They wanted to see, he says, whether “there is a way to capture that heat and use it in a passive approach.” They found that there was.

It’s not necessary to produce enough heat to melt the bulk of the ice that forms, the team found. All that’s needed is for the boundary layer, right where the ice meets the surface, to melt enough to create a thin layer of water, which will make the surface slippery enough so any ice will just slide right off. This is what the team has achieved with the three-layered material they’ve developed.

Layer by layer

The top layer is an absorber, which traps incoming sunlight and converts it to heat. The material the team used is highly efficient, absorbing 95 percent of the incident sunlight, and losing only 3 percent to re-radiation, Varanasi says

In principle, that layer could in itself help to prevent frost formation, but with two limitations: It would only work in the areas directly in sunlight, and much of the heat would be lost back into the substrate material — the airplane wing or powerline, for example — and would not help with the de-icing.

So, to compensate for the localization, the team added a spreader layer — a very thin layer of aluminum, just 400 micrometers thick, which is heated by the absorber layer above it and very efficiently spreads that heat out laterally to cover the entire surface. The material was selected to have “thermal response that is fast enough so that the heating takes place faster than the freezing,” Varanasi says.

Finally, the bottom layer is simply foam insulation, to keep any of that heat from being wasted downward and keep it where it’s needed, at the surface.

“In addition to passive de-icing, the photothermal trap stays at an elevated temperature, thus preventing ice build-up altogether,” Dash says.

The three layers, all made of inexpensive commercially available material, are then bonded together, and can be bonded to the surface that needs to be protected. For some applications, the materials could instead be sprayed onto a surface, one layer at a time, the researchers say.

The team carried out extensive tests, including real-world outdoor testing of the materials and detailed laboratory measurements, to prove the effectiveness of the system.

The system could even find wider commercial uses, such as panels to prevent icing on roofs of homes, schools, and other buildings, Varanasi says. The team is planning to continue work on the system, testing it for longevity and for optimal methods of application. But the basic system could essentially be applied almost immediately for some uses, especially stationary applications, he says.

“By harnessing acoustic forces, we have created a new technology that enables myriad materials to be printed in a drop-on-demand manner,” said Jennifer Lewis, the Hansjorg Wyss Professor of Biologically Inspired Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences and the senior author of the paper.

Lewis is also a Core Faculty Member at the Wyss Institute for Biologically Inspired Engineering and the Jianming Yu Professor of Arts and Sciences at Harvard.

The research is published in Science Advances.

Liquid droplets are used in many applications from printing ink on paper to creating microcapsules for drug delivery. Inkjet printing is the most common technique used to pattern liquid droplets, but it’s only suitable for liquids that are roughly 10 times more viscous than water. Yet many fluids of interest to researchers are far more viscous. For example, biopolymer and cell-laden solutions, which are vital for biopharmaceuticals and bioprinting, are at least 100 times more viscous than water. Some sugar-based biopolymers could be as viscous as honey, which is 25,000 times more viscous than water.

The viscosity of these fluids also changes dramatically with temperature and composition, makes it even more difficult to optimize printing parameters to control droplet sizes.

“Our goal was to take viscosity out of the picture by developing a printing system that is independent from the material properties of the fluid,” said Daniele Foresti, first author of the paper, the Branco Weiss Fellow and Research Associate in Materials Science and Mechanical Engineering at SEAS and the Wyss Institute.

To do that, the researchers turned to acoustic waves.

Thanks to gravity, any liquid can drip — from water dripping out of a faucet to the century-long pitch drop experiment. With gravity alone, droplet size remains large and drop rate difficult to control. Pitch, which has a viscosity roughly 200 billion times that of water, forms a single drop per decade.

To enhance drop formation, the research team relies on generating sound waves. These pressure waves have been typically used to defy gravity, as in the case of acoustic levitation. Now, the researchers are using them to assist gravity, dubbing this new technique acoustophoretic printing.

The researchers built a subwavelength acoustic resonator that can generate a highly confined acoustic field resulting in a pulling force exceeding 100 times the normal gravitation forces (1 G) at the tip of the printer nozzle — that’s more than four times the gravitational force on the surface of the sun.

This controllable force pulls each droplet off of the nozzle when it reaches a specific size and ejects it towards the printing target. The higher the amplitude of the sound waves, the smaller the droplet size, irrespective of the viscosity of the fluid.

“The idea is to generate an acoustic field that literally detaches tiny droplets from the nozzle, much like picking apples from a tree,” said Foresti.

The researchers tested the process on a wide range of materials from honey to stem-cell inks, biopolymers, optical resins and, even, liquid metals. Importantly, sound waves don’t travel through the droplet, making the method safe to use even with sensitive biological cargo, such as living cells or proteins.

“Our technology should have an immediate impact on the pharmaceutical industry,” said Lewis. “However, we believe that this will become an important platform for multiple industries.”

“This is an exquisite and impactful example of the breadth and reach of collaborative research,” said Dan Finotello, director of NSF’s MRSEC program. “The authors have developed a new printing platform using acoustic-forces, which, unlike in other methods, are material-independent and thus offer tremendous printing versatility. The application space is limitless.”

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

This research was co-authored by Katharina Kroll, Robert Amissah, Francesco Sillani, Kimberly Homan and Dimos Poulikakos. It was funded by Society in Science through the Branco Weiss Fellowship and the National Science Foundation through Harvard MRSEC.

Video: https://www.youtube.com/watch?v=FCbxfe9F6fs

The work, which appeared in the journal Cell Metabolism on August 30, 2018, suggests that the health problems associated with disruptions to animals’ 24-hour rhythms of activity and rest — which in humans is linked to eating for most of the day or doing shift work — can be corrected by eating all calories within a 10-hour window.

“For many of us, the day begins with a cup of coffee first thing in the morning and ends with a bedtime snack 14 or 15 hours later,” says Satchidananda Panda, a professor in Salk’s Regulatory Biology Laboratory and the senior author of the new paper. “But restricting food intake to 10 hours a day, and fasting the rest, can lead to better health, regardless of our biological clock.”

Every cell in mammals’ bodies operates on a 24-hour cycle known as the circadian rhythm — cellular cycles that govern when various genes are active. For example, in humans, genes for digestion are more active earlier in the day while genes for cellular repair are more active at night. Previously, the Panda lab discovered that mice allowed 24-hour access to a high-fat diet became obese and developed a slew of metabolic diseases including high cholesterol, fatty liver and diabetes. But these same mice, when restricted to the high-fat diet for a daily 8- to 10-hour window became lean, fit and healthy. The lab attributed the health benefits to keeping the mice in better sync with their cellular clocks — for example, by eating most of the calories when genes for digestion were more active.

In the current study, the team aimed to better understand the role of circadian rhythms in metabolic diseases by disabling genes responsible for maintaining the biological clock in mice, including in the liver, which regulates many metabolic functions. The genetic defects in these clock-less mice make them prone to obesity, diabetes, fatty liver disease and elevated blood cholesterol. These diseases further escalate when the animals are allowed to eat fatty and sugary food.

To test whether time-restricted eating could benefit these “clock-less” mice, Panda’s team put them on one of two high-fat diet regimes: one group had access to food around the clock, the other had access to the same number of calories only during a 10-hour window. As the team expected, the group that could eat at any time became obese and developed metabolic diseases. But the group that ate the same number of calories within a 10-hour window remained lean and healthy — despite not having an internal “biological clock” and thereby genetically programmed to be morbidly sick. This told the researchers that the health benefits from a 10-hour window were not just due to restricting eating to times when genes for digestion were more active.

“From the previous study, we had been under the impression that the biological clock was internally timing the process of turning genes for metabolism on and off at predetermined times,” says Amandine Chaix, a staff scientist at Salk and the paper’s first author. “And while that may still be true, this work suggests that by controlling the animals’ feeding and fasting cycles, we can basically override the lack of an internal timing system with an external timing system.”

According to the researchers, the new work suggests that the primary role of circadian clocks may be to tell the animal when to eat and when to stay away from food. This internal timing strikes a balance between sufficient nutrition during the fed state and necessary repair or rejuvenation during fasting. When this circadian clock is disrupted, as when humans do shift work, or when it is compromised due to genetic defects, the balance between nutrition and rejuvenation breaks down and diseases set in.

As we age, our circadian clocks weaken. This age-dependent deterioration of circadian clock parallels our increased risk for metabolic diseases, heart diseases, cancer and dementia.

But the good news, say the researchers, is that a simple lifestyle such as eating all food within 10 hours can restore balance, stave off metabolic diseases and maintain health. “Many of us may have one or more disease-causing defective genes that make us feel helpless and destined to be sick. The finding that a good lifestyle can beat the bad effects of defective genes opens new hope to stay healthy,” says Panda.

The lab next plans to study whether eating within 8-10 hours can prevent or reverse many diseases of aging, as well as looking at how the current study could apply to humans. Their website, mycircadianclock.org, allows people anywhere in the world to sign up for studies, download an app and get guidance on how to adopt an optimum daily eating-fasting cycle. By collecting daily eating and health status data from thousands of people, the lab hopes to gain a better understanding of how a daily eating-fasting cycle sustains health.

The findings, published in the journal PLOS Biology, suggest that targeting bile acid signaling in the brain may be a novel way to treat cocaine abuse.

Vanderbilt investigators Charles (Robb) Flynn, PhD, associate professor of Surgery, and Naji Abumrad, MD, John L. Sawyers Professor of Surgical Sciences, have long studied the metabolic changes associated with bariatric surgery for weight loss. Surgical patients experience dramatic changes in glucose regulation and in taste preferences and food cravings while they are still in the recovery room, Flynn said.

“These surgeries are doing something more than we understand. We wondered if elevated serum bile acids, a hallmark of bariatric surgery, were affecting the reward centers of the brain to blunt the pleasure of eating high-fat foods,” he said.

If the surgery did affect the brain’s reward centers, he added, “how might it impact the rewarding properties of drugs of abuse?”

The most commonly performed bariatric surgery — Roux-en-Y gastric bypass — restricts the size of the stomach and alters the path of food through the digestive tract. It also changes the point where bile acids enter the small intestine, from the usual upper part of the small intestine to a site near the end. The change increases circulating levels of bile acids in the body.

To explore the effects of bariatric surgery and elevated bile acids, Flynn’s group developed a simpler surgical procedure in mice called bile diversion, in which the gall bladder is surgically connected to the end of the small intestine. Bile diversion in an obese mouse produces all of the beneficial effects of bariatric surgery: weight loss, reduced food intake and improved oral glucose tolerance, Flynn said.

With colleague Aurelio Galli, PhD, a former Vanderbilt faculty member who is now at the University of Alabama at Birmingham, the investigators found that bile diversion surgery in normal-weight mice reduced cocaine-induced increases in brain dopamine release and reduced cocaine-associated behaviors.

The researchers tested the effects of a synthetic bile acid drug called obeticholic acid (OCA), which is clinically approved to treat the chronic liver disease primary biliary cholangitis. In mice without surgery, OCA administration mimicked the effects of bile diversion surgery in reducing cocaine-associated behaviors. The investigators further demonstrated that the bile acid receptor TGR5 mediates the effects of elevated bile acids and OCA in the nucleus accumbens, a brain region that plays a central role in reward circuitry.

The study is the first to demonstrate a central nervous system role for bile acids in altering reward-related behaviors, and it opens the possibility of treating drug abuse in new ways.

“Will bile acids cure cocaine addiction in humans? We don’t know, but our research certainly suggests that bariatric surgery or consumption of bile acids may have beneficial effects,” Flynn said.

“OCA is already clinically approved, so it might be possible to move quickly to clinical trials of its efficacy in treating addiction.”

The research team, made up of scientists from the National Institute of Environmental Health Sciences (NIEHS), part of NIH, and Rice University, Houston, also found that asthma patients that lack this genetic profile do not have the same sensitivity to traffic pollution and do not experience worse asthma symptoms. The work brings scientists closer to being able to use precision medicine, an emerging field that intends to prevent and treat disease based on factors specific to an individual.

Co-lead author Shepherd Schurman, M.D., associate medical director of the NIEHS Clinical Research Unit, stated the results are based on genetic variation, the subtle differences in DNA that make each person unique. He further added that to understand the concept, one should think of human genes, which are made up of DNA base pairs A, C, G, and T, as written instructions for making proteins.

“All humans have the same genes, in other words the same basic instructions, but in some people one DNA base pair has been changed,” Schurman said. “This common type of genetic variation is called a single nucleotide polymorphism or SNP, and it can alter the way proteins are made and make individuals more or less prone to illness.”

Schurman is also head of the Environmental Polymorphisms Registry (EPR), the DNA bank in North Carolina that provided volunteers for the study. The EPR studies how SNPs impact disease risk in combination with environmental exposures.

Together with NIEHS colleague and lung disease expert Stavros Garantziotis, M.D., medical director of the NIEHS Clinical Research Unit, the two scientists examined four SNPs that are involved in a biochemical pathway that leads to inflammatory responses in the body. They explained that SNPs are usually studied one at a time, but they wanted to learn if different combinations of these SNPs, along with pollution exposure, could worsen symptoms in a person with an inflammatory disease like asthma.

Schurman and Garantziotis gathered information about the SNPs, severity of asthma symptoms, and residential addresses of 2,704 EPR participants with asthma. Using the SNPs data, they divided the participants into three groups: hyper-responders, or those very sensitive to air pollution and likely to develop inflammation; hypo-responders, or those insensitive to air pollution and less likely to develop inflammation; and those in between. With the help of collaborators at Rice University, the team used the participants’ addresses to calculate their distance from a major road. Participants were categorized depending on whether they lived more or less than 275 yards from a major roadway. Data suggest that air pollution levels are elevated closer to major roads.

The researchers found that asthma sufferers who were hyper-responders and lived closer to heavily travelled roads had the worst asthma symptoms, such as difficulty breathing, chest pain, cough, and wheezing, compared to the other groups. In contrast, asthma patients who were hypo-responders and lived further away from busy roads had milder symptoms. Garantziotis concluded the work could greatly enhance the quality of life for people with asthma.

“Based on this research, we could propose that hyper-responders, who are exposed to traffic pollution, receive air purification intervention, such as HEPA filters, for their home,” Garantziotis said.

NIEHS Clinical Director Janet Hall, M.D., said the results emphasize the importance of gene-environment interactions in the progression of disease.

“This research is a great example of how we can approach disease prevention on a personal level, and tailor our treatments to suit individual patients,” she said. “That way we can be more efficient with our treatments and preventative measures, while at the same time cutting health care costs.”

Elastic synthetic materials such as silicone elastomers are very popular in industry. They are flexible, re-usable, cheap and easy to produce. They are therefore used for example as seals, for insulation or as corrosion protection. However, due to their low surface energy, they are hardly adhesive at all. This makes it difficult, for example, to paint silicone surfaces.

Surfaces with a mushroom-like microstructure adhere much better

Professor Stanislav N. Gorb and Emre Kizilkan from the Functional Morphology and Biomechanics working group are researching how to improve the adhesive properties of silicone elastomers. Their example to mimic is the surface structure of certain male leaf beetles (Chrysomelidae), looking like mushrooms. In two recent studies, they discovered that silicone elastomers adhere best if their surface is modified into mushroom-like structures and thereafter specifically treated with plasma. The electrically-charged gas which is the fourth state of matter, alongside solids, liquids and gases. Thus, the researchers combined a geometrical and a chemical method, to imitate biology. In addition, they showed that the degree of curvature of the materials affects their adhesion.

“Animals and plants provide us with a wealth of experience about some incredible features. We want to transfer the mechanisms behind them to artificial materials, to be able to control their behaviour in a targeted manner,” said the zoologist Gorb. Their goal of a reversible adhesion in the micro range without traditional glue could make completely new application possibilities conceivable — for example in micro-electronics.

During experimental tests silicones are curved

In a first step, the research team compared silicone elastomers of three different surfaces: one unstructured, one with pillar-shaped elements and a third with a mushroom-like structure. Using a micro-manipulator, they stuck a glass ball onto the surfaces and then removed it again. They tested how the adhesion changes when the materials with microstructured surfaces are bent convex (inwards) and concave (outwards). “In this way, we were able to demonstrate that silicone materials with a mushroom-like structure and curved concave have the double range of adhesive strength,” said doctoral researcher Emre Kizilkan, first author of the study. “With this surface structure, we can vary and control the adhesion of materials the most.”

Exact parameters for material-friendly plasma treatment

In a second step, the scientists treated the silicone elastomers with plasmas. This method is normally used to functionalise plastic materials, in order to increase their surface energy and to improve their adhesive properties. In comparison with other methods using liquids, plasma treatments can promise greater longevity — however, they often damage the surfaces of materials.

To find out how plasma treatments can significantly improve the adhesion of a material without damaging it, the scientists varied different parameters, such as the duration or the pressure. They found that the adhesion of unstructured surfaces on a glass substrate increased by approximately 30% after plasma treatment. On the mushroom-like structured surface the adhesion even increased by up to 91%. “These findings particularly surprised us, because the structured surface is only half as large as the unstructured, but adhesion enhancement was even three times better after the plasma treatment,” explained Kizilkan.

What happens when the treated and non-treated structured surfaces are removed from the glass substrate show the recordings with a high-speed camera: Because of its higher surface energy the plasma-treated microstructure remains fully in contact with the surface of the glass for 50,6 seconds. However, the contact area of the untreated microstructure is reduced quickly by around one third during the removal process, which is why the microstructure completely detaches from the glass substrate after 33 seconds already (Figure 3).

Especially suitable for applications in microelectronics

“We therefore have on a very small area an extremely strong adhesion with a wide range,” summarizes the material scientist Kizilkan. This makes the results especially interesting for small-scale applications such as micro-robots. The findings of the Kiel working group have already resulted in the development of an extremely strong adhesive tape, which functions according to the “gecko principle,” and can be removed without leaving any residue.

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That’s what a team of researchers led by WCS and WWF set out to discover — whether the comeback of a top predator — in this case lions in Laikipa County, Kenya — were recovering at the expense of Grevy’s zebras, which number only around 2,680 individuals with half of those living in Likipia.

In recent years, lion numbers have slowly recovered in this region as livestock ranching — which commonly practiced shooting or poisoning lions — has given way to wildlife tourism. Lions (Panthera leo) are classified as Threatened by IUCN.

Publishing their results in the journal PLOS ONE, the team used satellite telemetry to track the movements of both lions and zebras.

The team found that lions preyed on both Grevy’s and plains zebras (Equus quagga) far less than expected. Their data showed that the population of Grevy’s zebra populations may in fact be stabilizing with recruitment into the population tripling since 2004.

The researchers did conclude that competitive displacement by livestock and interference competition for grass from plains zebras, which are 22 times more abundant than Grevy’s, are most likely the predominant threat to Grevy’s zebras’ recovery.

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The findings, reported in Nature Communications, provide insights that may improve design of 2D materials for fast-charging energy-storage and electronic devices.

“Under our experimental conditions, titanium and carbon atoms can spontaneously form an atomically thin layer of 2D transition-metal carbide, which was never observed before,” said Xiahan Sang of ORNL.

He and ORNL’s Raymond Unocic led a team that performed in situ experiments using state-of-the-art scanning transmission electron microscopy (STEM), combined with theory-based simulations, to reveal the mechanism’s atomistic details.

“This study is about determining the atomic-level mechanisms and kinetics that are responsible for forming new structures of a 2D transition-metal carbide such that new synthesis methods can be realized for this class of materials,” Unocic added.

The starting material was a 2D ceramic called a MXene (pronounced “max een”). Unlike most ceramics, MXenes are good electrical conductors because they are made from alternating atomic layers of carbon or nitrogen sandwiched within transition metals like titanium.

The research was a project of the Fluid Interface Reactions, Structures and Transport (FIRST) Center, a DOE Energy Frontier Research Center that explores fluid-solid interface reactions that have consequences for energy transport in everyday applications. Scientists conducted experiments to synthesize and characterize advanced materials and performed theory and simulation work to explain observed structural and functional properties of the materials. New knowledge from FIRST projects provides guideposts for future studies.

The high-quality material used in these experiments was synthesized by Drexel University scientists, in the form of five-ply single-crystal monolayer flakes of MXene. The flakes were taken from a parent crystal called “MAX,” which contains a transition metal denoted by “M”; an element such as aluminum or silicon, denoted by “A”; and either a carbon or nitrogen atom, denoted by “X.” The researchers used an acidic solution to etch out the monoatomic aluminum layers, exfoliate the material and delaminate it into individual monolayers of a titanium carbide MXene (Ti3C2).

The ORNL scientists suspended a large MXene flake on a heating chip with holes drilled in it so no support material, or substrate, interfered with the flake. Under vacuum, the suspended flake was exposed to heat and irradiated with an electron beam to clean the MXene surface and fully expose the layer of titanium atoms.

MXenes are typically inert because their surfaces are covered with protective functional groups — oxygen, hydrogen and fluorine atoms that remain after acid exfoliation. After protective groups are removed, the remaining material activates. Atomic-scale defects — “vacancies” created when titanium atoms are removed during etching — are exposed on the outer ply of the monolayer. “These atomic vacancies are good initiation sites,” Sang said. “It’s favorable for titanium and carbon atoms to move from defective sites to the surface.” In an area with a defect, a pore may form when atoms migrate.

“Once those functional groups are gone, now you’re left with a bare titanium layer (and underneath, alternating carbon, titanium, carbon, titanium) that’s free to reconstruct and form new structures on top of existing structures,” Sang said.

High-resolution STEM imaging proved that atoms moved from one part of the material to another to build structures. Because the material feeds on itself, the growth mechanism is cannibalistic.

“The growth mechanism is completely supported by density functional theory and reactive molecular dynamics simulations, thus opening up future possibilities to use these theory tools to determine the experimental parameters required for synthesizing specific defect structures,” said Adri van Duin of Penn State.

Most of the time, only one additional layer [of carbon and titanium] grew on a surface. The material changed as atoms built new layers. Ti3C2 turned into Ti4C3, for example.

“These materials are efficient at ionic transport, which lends itself well to battery and supercapacitor applications,” Unocic said. “How does ionic transport change when we add more layers to nanometer-thin MXene sheets?” This question may spur future studies.

“Because MXenes containing molybdenum, niobium, vanadium, tantalum, hafnium, chromium and other metals are available, there are opportunities to make a variety of new structures containing more than three or four metal atoms in cross-section (the current limit for MXenes produced from MAX phases),” Yury Gogotsi of Drexel University added. “Those materials may show different useful properties and create an array of 2D building blocks for advancing technology.”

At ORNL’s Center for Nanophase Materials Sciences (CNMS), Yu Xie, Weiwei Sun and Paul Kent performed first-principles theory calculations to explain why these materials grew layer by layer instead of forming alternate structures, such as squares. Xufan Li and Kai Xiao helped understand the growth mechanism, which minimizes surface energy to stabilize atomic configurations. Penn State scientists conducted large-scale dynamical reactive force field simulations showing how atoms rearranged on surfaces, confirming defect structures and their evolution as observed in experiments.

The researchers hope the new knowledge will help others grow advanced materials and generate useful nanoscale structures.