Cellulose is a wonderful material for making hydrogels — which are used in applications ranging from contact lenses to wound care and drug delivery. But creating hydrogels from cellulose is tricky, and often the processes used to create the hydrogels are themselves toxic.

“Normally, you have to first dissolve the cellulose and then induce it to crosslink or form the structure of interest, which often requires the use of difficult to handle, unstable, or toxic solvents,” says Lucian Lucia, professor of forest biomaterials and chemistry at NC State and co-corresponding author of the work.

Enter the Swift family of birds — small birds who use their saliva to hold twigs in place when building their nests.

“My then Ph.D. student Zhen Zhang noted that when birds do this, the saliva acts like a natural resin that holds the nest together and encourages the fibers within the nest to interconnect or crosslink,” Lucia says. “Which is exactly what we want the dissolved cellulose to do when making hydrogels. So we asked ourselves, ‘what if we mimic the birds?'”

Zhang, currently a postdoc at Texas Tech University, is a co-corresponding author.

The researchers added a water soluble cellulose called carboxymethyl cellulose (CMC) to an acid solution and dissolved the CMC. Then they added powdered cellulose fiber to the solution and subjected it to four rounds of freezing and thawing. The result was cellulose gel.

“Think of it as adding a thickener to water, like you would a pie filling,” Lucia says. “By changing the pH of the CMC, the water essentially becomes sticky. Freezing and thawing the solution causes the cellulose to compact and interweave itself into the sticky network, giving you a more organized structure, just as Swifts do when they create their nests. Only we don’t have to use beaks and saliva to do it.”

Freeze drying the gels resulted in cellulose foam. The researchers repeated the process with bamboo fibers as well, which suggests that it could be useful with many other lignin and cellulose containing fibers.

“The cellulose gels are robust, stable at room temperature and can be tuned to degrade on a schedule, so would be useful in drug delivery applications, among others,” Lucia says. “This opens a promising new window for using biomimicry to process these insoluble cellulosic materials in a greener way.”

The work appears in Advanced Composites and Hybrid Materials. Noureddine Abidi of Texas Tech University is a co-corresponding author of the work.

Using tools hitched to the nose cone of their research planes and sampling more than 11 miles above the planet’s surface, researchers have discovered significant amounts of metals in aerosols in the atmosphere, likely from increasingly frequent launches and returns of spacecraft and satellites. That mass of metal is changing atmospheric chemistry in ways that may impact Earth’s atmosphere and ozone layer.

“We are finding this human-made material in what we consider a pristine area of the atmosphere,” said Dan Cziczo, one of a team of scientists who published a study on these results in the Proceedings of the National Academy of Sciences. “And if something is changing in the stratosphere — this stable region of the atmosphere — that deserves a closer look.” Cziczo, professor and head of the Department of Earth, Atmospheric, and Planetary Sciences in Purdue’s College of Science, is an expert in atmospheric science who has spent decades studying this rarefied region.

Led by Dan Murphy, an adjunct professor in the Department of Earth, Atmospheric, and Planetary Sciences and a researcher at the National Oceanic and Atmospheric Administration, the team detected more than 20 elements in ratios that mirror those used in spacecraft alloys. They found that the mass of lithium, aluminum, copper and lead from spacecraft reentry far exceeded those metals found in natural cosmic dust. Nearly 10% of large sulfuric acid particles — the particles that help protect and buffer the ozone layer — contained aluminum and other spacecraft metals.

Scientists estimate that as many as 50,000 more satellites may reach orbit by 2030. The team calculates that means that, in the next few decades, up to half of stratospheric sulfuric acid particles would contain metals from reentry. What effect that could have on the atmosphere, the ozone layer and life on Earth is yet to be understood.

Scientists have long suspected that spacecraft and satellites were changing the upper atmosphere, but studying the stratosphere, where we don’t live and even the highest flights enter only briefly, is challenging.

As part of NASA’s Airborne Science Program, Murphy and his group fly a WB-57 airplane to sample the atmosphere 11.8 miles (19 km) above the ground in Alaska, where circumpolar clouds tend to form. Similar measurements were made by Cziczo and his group from an ER-2 aircraft over the continental United States. Both groups use instruments hitched to the nose cone to ensure that only the freshest, most undisturbed air is sampled.

The sheltering sky

Like the view of the unruffled surface of the ocean, the stratosphere appears untroubled — at least to human eyes. Life and civilization take place mostly on the planet’s surface and in the troposphere, the atmosphere’s very lowest layer. The stratosphere is a surprisingly stable and seemingly serene layer of the atmosphere.

The stratosphere is also the realm of the ozone layer: that gaseous marvel that acts as a global tent to shield the planet and all life on it from the searing, scorching rays of ultraviolet radiation. Without the ozone layer, life would likely never have arisen on Earth. And without it, life is unlikely to be able to continue.

The last decades have been eventful for the stratosphere. The ozone layer came under threat from chlorofluorocarbons in the 1980s, and only coordinated, sustained global efforts of governments and corporations have begun to bear fruit in repairing and replenishing it.

“Shooting stars streak through the atmosphere,” Cziczo said. “Often, the meteor burns up in the atmosphere and doesn’t even become a meteorite and reach the planet. So the material it was made from stays in the atmosphere in the form of ions. They form very hot gas, which starts to cool and condense as molecules and fall into the stratosphere. The molecules find each other and knit together and form what we call meteorite smoke. Scientists recently started noticing that the chemical fingerprint of these meteoritic particles was starting to change, which made us ask, ‘Well, what changed?’ because meteorite composition hasn’t changed. But the number of spacecraft has.”

What goes up

Spacecraft launches, and returns, were once international events. The launches of Sputnik and the Mercury missions were front-page news. Now, a quickening tide of innovation and loosening regulation means that dozens of countries and corporations are able to launch satellites and spacecraft into orbit. All those satellites have to be sent up on rockets — and most of that material, eventually, comes back down.

Like the wakes of great ships trolling through the ocean, rockets leave behind them a trail of metals that may change the atmosphere in ways scientists don’t yet understand.

“Just to get things into orbit, you need all this fuel and a huge body to support the payload,” Cziczo said. “There are so many rockets going up and coming back and so many satellites falling back through the atmosphere that it’s starting to show up in the stratosphere as these aerosol particles.”

Of course, shooting stars were the first space-delivery system. Meteorites fall through the atmosphere every day. The heat and friction of the atmosphere peel material off them, just as they do off human-made artifacts. However, while hundreds of meteors enter the Earth’s atmosphere every day, they are increasingly being rivaled by the mass of metals that comprise the tons of Falcon, Ariane and Soyuz rockets that boost spacecraft into space and return again to Earth’s surface.

“Changes to the atmosphere can be difficult to study and complex to understand,” Cziczo said. “But what this research shows us is that the impact of human occupation and human spaceflight on the planet may be significant — perhaps more significant than we have yet imagined. Understanding our planet is one of the most urgent research priorities there is.”

And while most parents agree that kids benefit from opportunities to be independent, they may be engaging in more “helicopter parenting” than they realize, suggests a new University of Michigan Health C.S. Mott Children’s Hospital National Poll on Children’s Health.

“There’s a sizable gap between parent attitudes about promoting children’s independence and what they actually allow or encourage their children to do without supervision,” said Mott Poll co-director Sarah Clark, M.P.H.

“This suggests some parents may be missing opportunities to guide their children in tasks of autonomy and unintentionally hindering kids’ development of independence and problem-solving skills.”

Four in five parents of children ages 9-11 agree that it’s good for children to have free time without adult supervision. But fewer report their child actually does certain things without an adult present, the poll suggests.

About three in five parents have let their tween-aged child stay home for 30-60 minutes while half say their child has separated from them to find an item at another aisle in the store. Less than half say their child has waited in the car while the parent runs a quick errand, walked or biked to a friend’s house or played at the park with a friend, and less than a sixth of parents have let their child trick-or-treat with friends.

The top reason behind parents’ hesitancy to promote such independent milestones was safety. Yet, while a little more than half worried someone might scare or follow their child, just 17% of parents say their neighborhood is not safe for children to be alone.

“To some extent, worrying about your child is natural. But some parents are limiting their child’s independent activities due to highly publicized media reports, even if those outcomes are very unlikely to occur or cannot be prevented,” Clark said.

“Parents can ease in with small steps such as letting their child spend time with a friend at a familiar public place. Discussions before and after can help parents assess if their kids understand the importance of following safety rules.”

Other parents say they keep children from taking on such tasks alone because they don’t believe they’re ready while some parents believe state or local laws don’t allow children that age to be alone and that someone might call the police. A little more than one in 10 parents also think others will think they are a bad parent if their child is seen unsupervised.

Over half of parents say that unsupervised children cause trouble while a quarter have criticized another parent, and 13% have been criticized for not adequately supervising their child.

“Parents may be affected by ‘blame culture’ — the expectation that they will be criticized if something happens to their child,” Clark said.

The poll report also suggests a disconnect between what parents of younger children ages 5-8 say and what they do in fostering independence.

Nearly three quarters say they make it a point to have their child do things themselves. But less than half of these parents say their child regularly engages in actions such as talking with the doctor or nurse at health visits, deciding how to spend allowance or gift money, speaking to unfamiliar adults in business situations, such as ordering at a restaurant, or preparing their own meal or snack.

Among reasons were safety, getting stuck in habits, the parent belief that their child doesn’t want to do things themselves or isn’t mature enough, thinking it will take too long or that it won’t be done in the parent’s preferred way.

The elementary school years, Clark notes, is an important phase for developing independence with parental guidance.

“Becoming independent is a gradual process of allowing children increasing amounts of freedom, with parents there to teach skills and help the child understand the consequences of their choices,” Clark said.

“As children become more experienced and comfortable with tasks, they can assume responsibility for doing them regularly. Research shows encouraging independence fosters a child’s self-confidence, resilience, problem-solving ability, and mental health.”

The nationally representative poll is based on responses from 1,044 parents of children 5-11 years surveyed in August.

The automotive, aerospace, clean energy and tool-and-die industries — any industry that needs complex and high-performance parts — could use additive manufacturing,” said Alex Plotkowski, materials scientist in ORNL’s Materials Science and Technology Division and the lead scientist of the experiment. Plotkowski and his colleagues reported their findings in Nature Communications.

ORNL scientists have developed OpeN-AM, a 3D printing platform that can measure evolving residual stress during manufacturing using the VULCAN beamline at ORNL’s Spallation Neutron Source, or SNS, a Department of Energy Office of Science user facility. When combined with infrared imaging and computer modeling, this system enables unprecedented insight into material behavior during manufacturing.

In this case, they used low-temperature transformation, or LTT, steel, physically measuring how atoms move in response to stress, whether it’s temperature or load, using the OpeN-Am platform.

Residual stresses are stresses that remain even after a load or the cause of the stress is removed; they can deform a material or, worse, cause it to fail prematurely. Such stresses are a major challenge for fabricating accurate components with desirable properties and performance.

The scientists conceived and, over the course of two years, produced this experiment that can measure strain in the material as it evolves, which determines how stresses will be distributed.

“Manufacturers will be able to tailor residual stress in their components, increasing their strength, making them lighter and in more complex shapes. The technology can be applied to anything you want to manufacture,” Plotkowski said.

“We have successfully shown that there is a way to do that,” he said. “We are demonstrating we understand connections in one case to anticipate other cases.”

The scientists recently earned a 2023 R&D 100 Award for this technology. R&D World magazine announced the winners in August. Plotkowski and other winners will be recognized at the organization’s award ceremony Nov. 16 in San Diego.

The scientists used a custom wire-arc additive manufacturing platform to perform what’s called operando neutron diffraction of an LTT metal at SNS. Using SNS’s VULCAN beamline, they processed the steel and recorded data at various stages during manufacturing and after cooling to room temperature. They combined diffraction data with infrared imaging to confirm results. The system was designed and built at the Manufacturing Demonstration Facility, or MDF, a DOE Advanced Materials and Manufacturing Technologies Office user consortium, where a replicate system of the platform was also constructed to plan and test experiments before executing at the beamline.

SNS operates a linear particle accelerator that produces beams of neutrons to study and analyze materials at the atomic scale. The research tool they developed allows scientists to peer inside a material as it’s being produced, literally observing the mechanisms at work in real time.

The LTT steel was melted and deposited in layers. As the metal solidified and cooled, its structure transformed in what is called a phase transformation. When that happens, atoms rearrange and take up different space, and the material behaves differently.

Normally, transformations that happen at high temperatures are hard to understand when looking at a material only after processing. By observing the LTT steel during processing, the scientists’ experiment shows that they can understand and manipulate the phase transformation.

“We want to understand what these stresses are, explain how they got there, and figure out how to control them,” Plotkowski said.

“These results provide a new pathway to design desirable residual stress states and property distributions within additive manufacturing components by using process controls to improve nonuniform spatial and temporal variations of thermal gradients around key phase transformation temperatures,” the authors write.

Plotkowski hopes scientists from around the world come to ORNL to do similar experiments on metals they would like to use in manufacturing.

This research was funded by ORNL’s Laboratory Directed Research and Development program, which supports high-risk research and development in areas of potential high value to national programs.