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Saturday, April 08, 2023

Fully recyclable printed electronics ditch toxic chemicals for water

First-of-its-kind demonstration suggests a more environmentally friendly future for the electronics industry is possible

Peer-Reviewed Publication

DUKE UNIVERSITY

Printing Recyclable Transistors — VIDEO: AN INKJET PRINTER PUTS DOWN LAYERS OF CARBON-BASED ELECTRONIC INKS TO CREATE TRANSISTORS THAT CAN BE FULLY RECYCLED USING ONLY WATER, RATHER THAN REQUIRING HARSH, TOXIC CHEMICALS. view more
CREDIT: JASON ARTHURS PHOTOGRAPHY

DURHAM, N.C. – Engineers at Duke University have produced the world’s first fully recyclable printed electronics that replace the use of chemicals with water in the fabrication process. By bypassing the need for hazardous chemicals, the demonstration points down a path industry could follow to reduce its environmental footprint and human health risks.

The research appeared online Feb. 28 in the journal Nano Letters.

One of the dominant challenges facing any electronics manufacturer is successfully securing several layers of components on top of each other, which is crucial to making complex devices. Getting these layers to stick together can be a frustrating process, particularly for printed electronics.

“If you’re making a peanut butter and jelly sandwich, one layer on either slice of bread is easy,” explained Aaron Franklin, the Addy Professor of Electrical and Computer Engineering at Duke, who led the study. “But if you put the jelly down first and then try to spread peanut butter on top of it, forget it, the jelly won’t stay put and will intermix with the peanut butter. Putting layers on top of each other is not as easy as putting them down on their own — but that’s what you have to do if you want to build electronic devices with printing.”

In previous work, Franklin and his group demonstrated the first fully recyclable printed electronics. The devices used three carbon-based inks: semiconducting carbon nanotubes, conductive graphene and insulating nanocellulose. In trying to adapt the original process to only use water, the carbon nanotubes presented the largest challenge.

To make a water-based ink in which the carbon nanotubes don’t clump together and spread evenly on a surface, a surfactant similar to detergent is added. The resulting ink, however, does not create a layer of carbon nanotubes dense enough for a high current of electrons to travel across.

“You want the carbon nanotubes to look like al dente spaghetti strewn down on a flat surface,” said Franklin. “But with a water-based ink, they look more like they’ve been taken one-by-one and tossed on a wall to check for doneness. If we were using chemicals, we could just print multiple passes again and again until there were enough nanotubes. But water doesn’t work that way. We could do it 100 times and there’d still be the same density as the first time.”

This is because the surfactant used to keep the carbon nanotubes from clumping also prevents additional layers from adhering to the first. In a traditional manufacturing process, these surfactants would be removed using either very high temperatures, which takes a lot of energy, or harsh chemicals, which can pose human and environmental health risks. Franklin and his group wanted to avoid both.

In the paper, Franklin and his group develop a cyclical process in which the device is rinsed with water, dried in relatively low heat and printed on again. When the amount of surfactant used in the ink is also tuned down, the researchers show that their inks and processes can create fully functional, fully recyclable, fully water-based transistors.

Compared to a resistor or capacitor, a transistor is a relatively complex computer component used in devices such as power control or logic circuits and sensors. Franklin explains that, by demonstrating a transistor first, he hopes to signal to the rest of the field that there is a viable path toward making some electronics manufacturing processes much more environmentally friendly.

Franklin has already proven that nearly 100% of the carbon nanotubes and graphene used in printing can be recovered and reused in the same process, losing very little of the substances or their performance viability. Because nanocellulose is made from wood, it can simply be recycled or biodegraded like paper. And while the process does use a lot of water, it’s not nearly as much as what is required to deal with the toxic chemicals used in traditional fabrication methods.

According to a United Nations estimate, less than a quarter of the millions of pounds of electronics thrown away each year is recycled. And the problem is only going to get worse as the world eventually upgrades to 6G devices and the Internet of Things (IoT) continues to expand. So any dent that could be made in this growing mountain of electronic trash is important to pursue.

While more work needs to be done, Franklin says the approach could be used in the manufacturing of other electronic components like the screens and displays that are now ubiquitous to society. Every electronic display has a backplane of thin-film transistors similar to what is demonstrated in the paper. The current fabrication technology is high-energy and relies on hazardous chemicals as well as toxic gasses. The entire industry has been flagged for immediate attention by the US Environmental Protection Agency. [https://www.epa.gov/climateleadership/sector-spotlight-electronics]

“The performance of our thin-film transistors doesn’t match the best currently being manufactured, but they’re competitive enough to show the research community that we should all be doing more work to make these processes more environmentally friendly,” Franklin said.

This work was supported by the National Institutes of Health (1R01HL146849), the Air Force Office of Scientific Research (FA9550-22-1-0466), and the National Science Foundation (ECCS-1542015, Graduate Research Fellowship 2139754).

CITATION: “All-Carbon Thin-Film Transistors Using Water-Only Printing,” Shiheng Lu, Brittany N. Smith, Hope Meikle, Michael J. Therien, and Aaron D. Franklin. Nano Letters, Feb. 28, 2023. DOI: 10.1021/acs.nanolett.2c04196

An artistic depiction of the new process that allows printers to create fully functioning, fully recyclable transistors using only water instead of harsh chemicals.

CREDIT

Ella Maru Studios

JOURNAL

Nano Letters

DOI

10.1021/acs.nanolett.2c04196

METHOD OF RESEARCH

Experimental study

SUBJECT OF RESEARCH

Not applicable

ARTICLE TITLE

All-Carbon Thin-Film Transistors Using Water-Only Printing

Broccoli consumption protects gut lining, reduces disease, in mice

Researchers discover that a certain molecule in broccoli interacts with a receptor in mice to promote gut health

Peer-Reviewed Publication

PENN STATE

UNIVERSITY PARK, Pa. — Broccoli is known to be beneficial to our health. For example, research has shown that increased consumption of the cruciferous vegetable decreases incidences of cancer and type 2 diabetes. In a recent study, researchers at Penn State found that broccoli contains certain molecules that bind to a receptor within mice and help to protect the lining of the small intestine, thereby inhibiting the development of disease. The findings lend support to the idea that broccoli truly is a ‘superfood.’

“We all know that broccoli is good for us, but why? What happens in the body when we eat broccoli?” said Gary Perdew, H. Thomas and Dorothy Willits Hallowell Chair in Agricultural Sciences, Penn State. “Our research is helping to uncover the mechanisms for how broccoli and other foods benefit health in mice and likely humans, as well. It provides strong evidence that cruciferous vegetables, such as broccoli, cabbage, and Brussels sprouts should be part of a normal healthy diet.”

According to Perdew, the wall of the small intestine allows beneficial water and nutrients to pass into the body but prevents food particles and bacteria that could cause harm. Certain cells that line the intestine — including enterocytes, which absorb water and nutrients; goblet cells, which secrete a protective layer of mucus on the intestinal wall; and Paneth cells, which secrete lysosomes that contain digestive enzymes — help to modulate this activity and keep a healthy balance.

In their study, which published in the journal Laboratory Investigation, Perdew and his colleagues found that molecules in broccoli, called aryl hydrocarbon receptor ligands, bind to aryl hydrocarbon receptor (AHR), which is a type of protein called a transcription factor. This binding, they found, initiates a variety of activities that affect the functions of intestinal cells.

To conduct their study, the researchers fed an experimental group of mice a diet containing 15% broccoli — equivalent to about 3.5 cups per day for humans — and fed a control group of mice a typical lab diet that did not contain broccoli. They then analyzed the animals’ tissues to determine the extent to which AHR was activated, as well as the quantities of various cell types and mucus concentrations, among other factors, in the two groups.

The team found that mice that were not fed broccoli lacked AHR activity, which resulted in altered intestinal barrier function, reduced transit time of food in the small intestine, decreased number of goblet cells and protective mucus, decreased Paneth cells and lysosome production, and decreased number of enterocyte cells.

“The gut health of the mice that were not fed broccoli was compromised in a variety of ways that are known to be associated with disease,” said Perdew. “Our research suggests that broccoli and likely other foods can be used as natural sources of AHR ligands, and that diets rich in these ligands contribute to resilience of the small intestine.”

More broadly, added Andrew Patterson, John T. and Paige S. Smith Professor of Molecular Toxicology and of Biochemistry and Molecular Biology, “these data suggest that dietary cues, relayed through the activity of AHR, can reshape the cellular and metabolic repertoire of the gastrointestinal tract.”

Other authors on the paper include Xiaoliang Zhou, Debopriya Chakraborty, Iain A. Murray, Denise Coslo, Zoe Kehs, Anitha Vijay, Carolyn Ton, Dhimant Desai and Shantu G. Amin.

The National Institutes of Health Grants, U.S. Department of Agriculture and Penn State Cancer Institute supported this research.

JOURNAL

Laboratory Investigation

DOI

10.1016/j.labinv.2022.100012

Sierra squirrels find their niche amid a changing climate

Climate change not the only important thing for a species’ niche

NEWS RELEASE 6-APR-2023

UNIVERSITY OF CALIFORNIA - DAVIS

Yellow-bellied marmot in Sierra Nevada landscape — IMAGE: A YELLOW-BELLIED MARMOT LOOKS ACROSS A SIERRA NEVADA LANDSCAPE. view more
CREDIT: AVIVA ROSSI/UC DAVIS

As the climate changes, many species are expected to adjust where and how they live. Some are expected to seek cooler elevations as it warms, but what happens to species already at the top of a mountain? A study of squirrels living in California’s high-elevation Sierra Nevada indicates that climate is only one factor to consider when trying to predict where an animal will make its home in a changing world.

The study, led by the University of California, Davis, is published in the journal Ecology and Evolution and was conducted in alpine regions stretching nearly 200 miles from Alpine County just south of Lake Tahoe, along the spine of the Sierra and south to Tulare and Inyo counties.

The study characterizes the niche space of three species of squirrel: the yellow-bellied marmot, Belding’s ground squirrel and the golden-mantled ground squirrel. The authors analyzed nearly 6,000 observations of individual squirrels, collected from field survey data conducted over four years.

For this study, the “niche” describes all the conditions in the environment that are important for an animal to live in an area. Understanding the niche of animals helps scientists learn which changes are expected to most impact a species and, therefore, which animals may be most vulnerable to climate change.

“We’re trying from a conservation perspective to understand what will happen to these species as the world changes,” said lead author Aviva Rossi, who conducted the study while a UC Davis graduate student in the Department of Wildlife, Fish and Conservation Biology. “A quantitative analysis of what makes a species able to live where it lives allows us to bring that information forward, and better understand differences between species.”

What doesn’t change

Niche was defined not only by climate, but also by topography (like how steep an area was) and land cover (such as meadows or forests). Some of these nonclimate environmental conditions, like slope or the presence of rocks, rarely change.

Although all three squirrel species occur in the same region, they each use that space a little differently because their niche is different.

Grassland meadows were particularly important for yellow-bellied marmots and the Belding’s ground squirrel. Yet, within a meadow, marmots preferred drier conditions, while Belding’s ground squirrels favored wet vegetation.

Golden-mantled squirrels — a common sight at area campgrounds — preferred forested areas and do well with more snow-free days. Belding’s ground squirrels preferred having snow on the ground longer.

Even with these overall selection patterns, there can still be too much of a good thing in extreme years, Rossi said.

Mammals in high-elevation mountains are often perceived as vulnerable to climate shifts, the study notes. Yet, the results underscore the importance of including factors that go beyond climate when defining their niche.

Making better decisions

Rossi notes that climate change is often viewed through a lens of hope or despair, but the study illustrated how its impacts are more complex.

“There’s hope in some areas and not in others,” Rossi said. “If one species is there because of a meadow and another is there because of an outcropping of rocks, as the world changes, it may change where one species lives but not the other. We just want to better understand what’s likely to happen so we can make better conservation decisions.”

The study’s co-authors include Robert Klinger of the U.S. Geological Survey, and Elise Hellwig and Dirk Van Vuren of the UC Davis Department of Wildlife Fish and Conservation Biology.

The study was funded through the USGS National Climate Change and Wildlife Science Center, Yosemite National Park, Sequoia and Kings Canyon National Parks, with support from the Gulch Environmental Foundation.

Belding’s ground squirrels favor wet vegetation in the mountains.