Tag Archives: University of Pennsylvania

“The earth is mostly made of cubes,” said Plato in 5th Century BCE. Turns out, he was right!

Theories from mathematics, physics, and geology have been used to demonstrate that the earth’s basic shape is, roughly speaking, a cube. From a July 20, 2020 news item on ScienceDaily,

Plato, the Greek philosopher who lived in the 5th century B.C.E. [before the common era], believed that the universe was made of five types of matter: earth, air, fire, water, and cosmos. Each was described with a particular geometry, a platonic shape. For earth, that shape was the cube.

Science has steadily moved beyond Plato’s conjectures, looking instead to the atom as the building block of the universe. Yet Plato seems to have been onto something, researchers have found.

In a new paper in the Proceedings of the National Academy of Sciences [PNAS], a team from the University of Pennsylvania, Budapest University of Technology and Economics, and University of Debrecen [Hungary] uses math, geology, and physics to demonstrate that the average shape of rocks on Earth is a cube.

A July 17, 2020 University of Pennsylvania news release (also on EurekAlert but dated July 20, 2020), which originated the news item, goes on to describe the work as “mind-blowing,”

“Plato is widely recognized as the first person to develop the concept of an atom [Maybe not, scroll down to find the subhead “Leucippus and Democritus”], the idea that matter is composed of some indivisible component at the smallest scale,” says Douglas Jerolmack, a geophysicist in Penn’s School of Arts & Sciences’ Department of Earth and Environmental Science and the School of Engineering and Applied Science’s Department of Mechanical Engineering and Applied Mechanics. “But that understanding was only conceptual; nothing about our modern understanding of atoms derives from what Plato told us.

“The interesting thing here is that what we find with rock, or earth, is that there is more than a conceptual lineage back to Plato. It turns out that Plato’s conception about the element earth being made up of cubes is, literally, the statistical average model for real earth. And that is just mind-blowing.”

The group’s finding began with geometric models developed by mathematician Gábor Domokos of the Budapest University of Technology and Economics, whose work predicted that natural rocks would fragment into cubic shapes.

“This paper is the result of three years of serious thinking and work, but it comes back to one core idea,” says Domokos. “If you take a three-dimensional polyhedral shape, slice it randomly into two fragments and then slice these fragments again and again, you get a vast number of different polyhedral shapes. But in an average sense, the resulting shape of the fragments is a cube.”

Domokos pulled two Hungarian theoretical physicists into the loop: Ferenc Kun, an expert on fragmentation, and János Török, an expert on statistical and computational models. After discussing the potential of the discovery, Jerolmack says, the Hungarian researchers took their finding to Jerolmack to work together on the geophysical questions; in other words, “How does nature let this happen?”

“When we took this to Doug, he said, ‘This is either a mistake, or this is big,'” Domokos recalls. “We worked backward to understand the physics that results in these shapes.”

Fundamentally, the question they answered is what shapes are created when rocks break into pieces. Remarkably, they found that the core mathematical conjecture unites geological processes not only on Earth but around the solar system as well.

“Fragmentation is this ubiquitous process that is grinding down planetary materials,” Jerolmack says. “The solar system is littered with ice and rocks that are ceaselessly smashing apart. This work gives us a signature of that process that we’ve never seen before.”

Part of this understanding is that the components that break out of a formerly solid object must fit together without any gaps, like a dropped dish on the verge of breaking. As it turns out, the only one of the so-called platonic forms–polyhedra with sides of equal length–that fit together without gaps are cubes.

“One thing we’ve speculated in our group is that, quite possibly Plato looked at a rock outcrop and after processing or analyzing the image subconsciously in his mind, he conjectured that the average shape is something like a cube,” Jerolmack says.

“Plato was very sensitive to geometry,” Domokos adds. According to lore, the phrase “Let no one ignorant of geometry enter” was engraved at the door to Plato’s Academy. “His intuitions, backed by his broad thinking about science, may have led him to this idea about cubes,” says Domokos.

To test whether their mathematical models held true in nature, the team measured a wide variety of rocks, hundreds that they collected and thousands more from previously collected datasets. No matter whether the rocks had naturally weathered from a large outcropping or been dynamited out by humans, the team found a good fit to the cubic average.

However, special rock formations exist that appear to break the cubic “rule.” The Giant’s Causeway in Northern Ireland, with its soaring vertical columns, is one example, formed by the unusual process of cooling basalt. These formations, though rare, are still encompassed by the team’s mathematical conception of fragmentation; they are just explained by out-of-the-ordinary processes at work.

“The world is a messy place,” says Jerolmack. “Nine times out of 10, if a rock gets pulled apart or squeezed or sheared–and usually these forces are happening together–you end up with fragments which are, on average, cubic shapes. It’s only if you have a very special stress condition that you get something else. The earth just doesn’t do this often.”

The researchers also explored fragmentation in two dimensions, or on thin surfaces that function as two-dimensional shapes, with a depth that is significantly smaller than the width and length. There, the fracture patterns are different, though the central concept of splitting polygons and arriving at predictable average shapes still holds.

“It turns out in two dimensions you’re about equally likely to get either a rectangle or a hexagon in nature,” Jerolmack says. “They’re not true hexagons, but they’re the statistical equivalent in a geometric sense. You can think of it like paint cracking; a force is acting to pull the paint apart equally from different sides, creating a hexagonal shape when it cracks.”

In nature, examples of these two-dimensional fracture patterns can be found in ice sheets, drying mud, or even the earth’s crust, the depth of which is far outstripped by its lateral extent, allowing it to function as a de facto two-dimensional material. It was previously known that the earth’s crust fractured in this way, but the group’s observations support the idea that the fragmentation pattern results from plate tectonics.

Identifying these patterns in rock may help in predicting phenomenon such as rock fall hazards or the likelihood and location of fluid flows, such as oil or water, in rocks.

For the researchers, finding what appears to be a fundamental rule of nature emerging from millennia-old insights has been an intense but satisfying experience.

“There are a lot of sand grains, pebbles, and asteroids out there, and all of them evolve by chipping in a universal manner,” says Domokos, who is also co-inventor of the Gömböc, the first known convex shape with the minimal number–just two–of static balance points. Chipping by collisions gradually eliminates balance points, but shapes stop short of becoming a Gömböc; the latter appears as an unattainable end point of this natural process.

The current result shows that the starting point may be a similarly iconic geometric shape: the cube with its 26 balance points. “The fact that pure geometry provides these brackets for a ubiquitous natural process, gives me happiness,” he says.

“When you pick up a rock in nature, it’s not a perfect cube, but each one is a kind of statistical shadow of a cube,” adds Jerolmack. “It calls to mind Plato’s allegory of the cave. He posited an idealized form that was essential for understanding the universe, but all we see are distorted shadows of that perfect form.”

The human capacity for imagination, in this case linking ideas about geometry and mathematics from the 5th Century BCE to modern physics and geology and to the solar system, astounds and astonishes me. As for Jerolmack’s comment that Plato (428/427 or 424/423 – 348/347 BC) was the first to develop the concept of an atom, not everyone agrees.

Leucippus and Democritus

It may not ever be possible to determine who was the first to theorize/philosophize about atoms but there is relatively general agreement that Leucippus (5th cent.BCE) and his successor, Democritus (c. 460 – c. 370 BC) were among the first. Here’s more about Ancient Atomism and its origins from the Stanford Encyclopedia of Philosphy,

Leucippus (5th c. BCE) is the earliest figure whose commitment to atomism is well attested. He is usually credited with inventing atomism. According to a passing remark by the geographer Strabo, Posidonius (1st c. BCE Stoic philosopher) reported that ancient Greek atomism can be traced back to a figure known as Moschus or Mochus of Sidon, who lived at the time of the Trojan wars. This report was given credence in the seventeenth century: the Cambridge Platonist Henry More traced the origins of ancient atomism back, via Pythagoras and Moschus, to Moses. This theologically motivated view does not seem to claim much historical evidence, however.

Leucippus and Democritus are widely regarded as the first atomists [emphasis mine] in the Greek tradition. Little is known about Leucippus, while the ideas of his student Democritus—who is said to have taken over and systematized his teacher’s theory—are known from a large number of reports. These ancient atomists theorized that the two fundamental and oppositely characterized constituents of the natural world are indivisible bodies—atoms—and void. The latter is described simply as nothing, or the negation of body. Atoms are by their nature intrinsically unchangeable; they can only move about in the void and combine into different clusters. Since the atoms are separated by void, they cannot fuse, but must rather bounce off one another when they collide. Because all macroscopic objects are in fact combinations of atoms, everything in the macroscopic world is subject to change, as their constituent atoms shift or move away. Thus, while the atoms themselves persist through all time, everything in the world of our experience is transitory and subject to dissolution.

Although the Greek term atomos is most commonly associated with the philosophical system developed by Leucippus and Democritus, involving solid and impenetrable bodies, Plato’s [emphasis mine] Timaeus presents a different kind of physical theory based on indivisibles. The dialogue elaborates an account of the world wherein the four different basic kinds of matter—earth, air, fire, and water—are regular solids composed from plane figures: isoceles and scalene right-angled triangles. Because the same triangles can form into different regular solids, the theory thus explains how some of the elements can transform into one another, as was widely believed.

As you can see from the excerpt, they are guessing as to the source for atomism and thee are different kinds of atomism and Plato staked his own atomistic territory.

The paper

Here’s a link to and a citation for the paper followed by a statement of significance and the paper’s abstract,

Plato’s cube and the natural geometry of fragmentation by Gábor Domokos, Douglas J. Jerolmack, Ferenc Kun, and János Török. PNAS DOI: https://doi.org/10.1073/pnas.2001037117 First published July 17, 2020

This paper is behind a paywall.

Now for the Significance and the Abstract,

We live on and among the by-products of fragmentation, from nanoparticles to rock falls to glaciers to continents. Understanding and taming fragmentation is central to assessing natural hazards and extracting resources, and even for landing probes safely on other planetary bodies. In this study, we draw inspiration from an unlikely and ancient source: Plato, who proposed that the element Earth is made of cubes because they may be tightly packed together. We demonstrate that this idea is essentially correct: Appropriately averaged properties of most natural 3D fragments reproduce the topological cube. We use mechanical and geometric models to explain the ubiquity of Plato’s cube in fragmentation and to uniquely map distinct fragment patterns to their formative stress conditions.

Plato envisioned Earth’s building blocks as cubes, a shape rarely found in nature. The solar system is littered, however, with distorted polyhedra—shards of rock and ice produced by ubiquitous fragmentation. We apply the theory of convex mosaics to show that the average geometry of natural two-dimensional (2D) fragments, from mud cracks to Earth’s tectonic plates, has two attractors: “Platonic” quadrangles and “Voronoi” hexagons. In three dimensions (3D), the Platonic attractor is dominant: Remarkably, the average shape of natural rock fragments is cuboid. When viewed through the lens of convex mosaics, natural fragments are indeed geometric shadows of Plato’s forms. Simulations show that generic binary breakup drives all mosaics toward the Platonic attractor, explaining the ubiquity of cuboid averages. Deviations from binary fracture produce more exotic patterns that are genetically linked to the formative stress field. We compute the universal pattern generator establishing this link, for 2D and 3D fragmentation.

Fascinating, eh?

Iridescent giant clams could point the way to safety, climatologically speaking

Giant clams in Palau (Cynthia Barnett)

These don’t look like any clams I’ve ever seen but that is the point of Cynthia Barnett’s absorbing Sept. 10, 2018 article for The Atlantic (Note: A link has been removed),

Snorkeling amid the tree-tangled rock islands of Ngermid Bay in the western Pacific nation of Palau, Alison Sweeney lingers at a plunging coral ledge, photographing every giant clam she sees along a 50-meter transect. In Palau, as in few other places in the world, this means she is going to be underwater for a skin-wrinkling long time.

At least the clams are making it easy for Sweeney, a biophysicist at the University of Pennsylvania. The animals plump from their shells like painted lips, shimmering in blues, purples, greens, golds, and even electric browns. The largest are a foot across and radiate from the sea floor, but most are the smallest of the giant clams, five-inch Tridacna crocea, living higher up on the reef. Their fleshy Technicolor smiles beam in all directions from the corals and rocks of Ngermid Bay.

… Some of the corals are bleached from the conditions in Ngermid Bay, where naturally high temperatures and acidity mirror the expected effects of climate change on the global oceans. (Ngermid Bay is more commonly known as “Nikko Bay,” but traditional leaders and government officials are working to revive the indigenous name of Ngermid.)

Even those clams living on bleached corals are pulsing color, like wildflowers in a white-hot desert. Sweeney’s ponytail flows out behind her as she nears them with her camera. They startle back into their fluted shells. Like bashful fairytale creatures cursed with irresistible beauty, they cannot help but draw attention with their sparkly glow.

Barnett makes them seem magical and perhaps they are (Note: A link has been removed),

It’s the glow that drew Sweeney’s attention to giant clams, and to Palau, a tiny republic of more than 300 islands between the Philippines and Guam. Its sun-laden waters are home to seven of the world’s dozen giant-clam species, from the storied Tridacna gigas—which can weigh an estimated 550 pounds and measure over four feet across—to the elegantly fluted Tridacna squamosa. Sweeney first came to the archipelago in 2009, while working on animal iridescence as a post-doctoral fellow at the University of California at Santa Barbara. Whether shimmering from a blue morpho butterfly’s wings or a squid’s skin, iridescence is almost always associated with a visual signal—one used to attract mates or confuse predators. Giant clams’ luminosity is not such a signal. So, what is it?

In the years since, Sweeney and her colleagues have discovered that the clams’ iridescence is essentially the outer glow of a solar transformer—optimized over millions of years to run on sunlight and algal biofuel. Giant clams reach their cartoonish proportions thanks to an exceptional ability to grow their own photosynthetic algae in vertical farms spread throughout their flesh. Sweeney and other scientists think this evolved expertise may shed light on alternative fuel technologies and other industrial solutions for a warming world.

Barnett goes on to describe Palau’s relationship to the clams and the clams’ environment,

Palau’s islands have been inhabited for at least 3,400 years, and from the start, giant clams were a staple of diet, daily life, and even deity. Many of the islands’ oldest-surviving tools are crafted of thick giant-clam shell: arched-blade adzes, fishhooks, gougers, heavy taro-root pounders. Giant-clam shell makes up more than three-fourths of some of the oldest shell middens in Palau, a percentage that decreases through the centuries. Archaeologists suggest that the earliest islanders depleted the giant clams that crowded the crystalline shallows, then may have self-corrected. Ancient Palauan conservation law, known as bul, prohibited fishing during critical spawning periods, or when a species showed signs of over-harvesting.

Before the Christianity that now dominates Palauan religion sailed in on eighteenth-century mission ships, the culture’s creation lore began with a giant clam called to life in an empty sea. The clam grew bigger and bigger until it sired Latmikaik, the mother of human children, who birthed them with the help of storms and ocean currents.

The legend evokes giant clams in their larval phase, moving with the currents for their first two weeks of life. Before they can settle, the swimming larvae must find and ingest one or two photosynthetic alga, which later multiply, becoming self-replicating fuel cells. After the larvae down the alga and develop a wee shell and a foot, they kick around like undersea farmers, looking for a sunny spot for their crop. When they’ve chosen a well-lit home in a shallow lagoon or reef, they affix to the rock, their shell gaping to the sky. After the sun hits and photosynthesis begins, the microalgae will multiply to millions, or in the case of T. gigas, billions, and clam and algae will live in symbiosis for life.

Giant clam is a beloved staple in Palau and many other Pacific islands, prepared raw with lemon, simmered into coconut soup, baked into a savory pancake, or sliced and sautéed in a dozen other ways. But luxury demand for their ivory-like shells and their adductor muscle, which is coveted as high-end sashimi and an alleged aphrodisiac, has driven T. gigas extinct in China, Taiwan, and other parts of their native habitat. Some of the toughest marine-protection laws in the world, along with giant-clam aquaculture pioneered here, have helped Palau’s wild clams survive. The Palau Mariculture Demonstration Center raises hundreds of thousands of giant clams a year, supplying local clam farmers who sell to restaurants and the aquarium trade and keeping pressure off the wild population. But as other nations have wiped out their clams, Palau’s 230,000-square-mile ocean territory is an increasing target of illegal foreign fishers.

Barnett delves into how the country of Palau is responding to the voracious appetite for the giant clams and other marine life,

Palau, drawing on its ancient conservation tradition of bul, is fighting back. In 2015, President Tommy Remengesau Jr. signed into law the Palau National Marine Sanctuary Act, which prohibits fishing in 80 percent of Palau’s Exclusive Economic Zone and creates a domestic fishing area in the remaining 20 percent, set aside for local fishers selling to local markets. In 2016, the nation received a $6.6 million grant from Japan to launch a major renovation of the Palau Mariculture Demonstration Center. Now under construction at the waterfront on the southern tip of Malakal Island, the new facility will amp up clam-aquaculture research and increase giant-clam production five-fold, to more than a million seedlings a year.

Last year, Palau amended its immigration policy to require that all visitors sign a pledge to behave in an ecologically responsible manner. The pledge, stamped into passports by an immigration officer who watches you sign, is written to the island’s children:

Children of Palau, I take this pledge, as your guest, to preserve and protect your beautiful and unique island home. I vow to tread lightly, act kindly and explore mindfully. I shall not take what is not given. I shall not harm what does not harm me. The only footprints I shall leave are those that will wash away.

The pledge is winning hearts and public-relations awards. But Palau’s existential challenge is still the collective “we,” the world’s rising carbon emissions and the resulting upturns in global temperatures, sea levels, and destructive storms.

F. Umiich Sengebau, Palau’s Minister for Natural Resources, Environment, and Tourism, grew up on Koror and is full of giant-clam proverbs, wisdom and legends from his youth. He tells me a story I also heard from an elder in the state of Airai: that in old times, giant clams were known as “stormy-weather food,” the fresh staple that was easy to collect and have on hand when it was too stormy to go out fishing.

As Palau faces the storms of climate change, Sengebau sees giant clams becoming another sort of stormy-weather food, serving as a secure source of protein; a fishing livelihood; a glowing icon for tourists; and now, an inspiration for alternative energy and other low-carbon technologies. “In the old days, clams saved us,” Sengebau tells me. “I think there’s a lot of power in that, a great power and meaning in the history of clams as food, and now clams as science.”

I highly recommend Barnett’s article, which is one article in a larger series, from a November 6, 2017 The Atlantic press release,

The Atlantic is expanding the global footprint of its science writing today with a multi-year series to investigate life in all of its multitudes. The series, “Life Up Close,” created with support from Howard Hughes Medical Institute’s Department of Science Education (HHMI), begins today at TheAtlantic.com. In the first piece for the project, “The Zombie Diseases of Climate Change,” The Atlantic’s Robinson Meyer travels to Greenland to report on the potentially dangerous microbes emerging from thawing Arctic permafrost.

The project is ambitious in both scope and geographic reach, and will explore how life is adapting to our changing planet. Journalists will travel the globe to examine these changes as they happen to microbes, plants, and animals in oceans, grasslands, forests, deserts, and the icy poles. The Atlantic will question where humans should look for life next: from the Martian subsurface, to Europa’s oceans, to the atmosphere of nearby stars and beyond. “Life Up Close” will feature at least twenty reported pieces continuing through 2018.

“The Atlantic has been around for 160 years, but that’s a mere pinpoint in history when it comes to questions of life and where it started, and where we’re going,” said Ross Andersen, The Atlantic’s senior editor who oversees science, tech, and health. “The questions that this project will set out to tackle are critical; and this support will allow us to cover new territory in new and more ambitious ways.”

About The Atlantic:
Founded in 1857 and today one of the fastest growing media platforms in the industry, The Atlantic has throughout its history championed the power of big ideas and continues to shape global debate across print, digital, events, and video platforms. With its award-winning digital presence TheAtlantic.com and CityLab.com on cities around the world, The Atlantic is a multimedia forum on the most critical issues of our times—from politics, business, urban affairs, and the economy, to technology, arts, and culture. The Atlantic is celebrating its 160th anniversary this year. Bob Cohn is president of The Atlantic and Jeffrey Goldberg is editor in chief.

About the Howard Hughes Medical Institute (HHMI) Department of Science Education:
HHMI is the leading private nonprofit supporter of scientific research and science education in the United States. The Department of Science Education’s BioInteractive division produces free, high quality educational media for science educators and millions of students around the globe, its HHMI Tangled Bank Studios unit crafts powerful stories of scientific discovery for television and big screens, and its grants program aims to transform science education in universities and colleges. For more information, visit www.hhmi.org.

Getting back to the giant clams, sometimes all you can do is marvel, eh?

Transparent graphene electrode technology and complex brain imaging

Michael Berger has written a May 24, 2018 Nanowerk Spotlight article about some of the latest research on transparent graphene electrode technology and the brain (Note: A link has been removed),

In new work, scientists from the labs of Kuzum [Duygu Kuzum, an Assistant Professor of Electrical and Computer Engineering at the University of California, San Diego {UCSD}] and Anna Devor report a transparent graphene microelectrode neural implant that eliminates light-induced artifacts to enable crosstalk-free integration of 2-photon microscopy, optogenetic stimulation, and cortical recordings in the same in vivo experiment. The new class of transparent brain implant is based on monolayer graphene. It offers a practical pathway to investigate neuronal activity over multiple spatial scales extending from single neurons to large neuronal populations.

Conventional metal-based microelectrodes cannot be used for simultaneous measurements of multiple optical and electrical parameters, which are essential for comprehensive investigation of brain function across spatio-temporal scales. Since they are opaque, they block the field of view of the microscopes and generate optical shadows impeding imaging.

More importantly, they cause light induced artifacts in electrical recordings, which can significantly interfere with neural signals. Transparent graphene electrode technology presented in this paper addresses these problems and allow seamless and crosstalk-free integration of optical and electrical sensing and manipulation technologies.

In their work, the scientists demonstrate that by careful design of key steps in the fabrication process for transparent graphene electrodes, the light-induced artifact problem can be mitigated and virtually artifact-free local field potential (LFP) recordings can be achieved within operating light intensities.

“Optical transparency of graphene enables seamless integration of imaging, optogenetic stimulation and electrical recording of brain activity in the same experiment with animal models,” Kuzum explains. “Different from conventional implants based on metal electrodes, graphene-based electrodes do not generate any electrical artifacts upon interacting with light used for imaging or optogenetics. That enables crosstalk free integration of three modalities: imaging, stimulation and recording to investigate brain activity over multiple spatial scales extending from single neurons to large populations of neurons in the same experiment.”

The team’s new fabrication process avoids any crack formation in the transfer process, resulting in a 95-100% yield for the electrode arrays. This fabrication quality is important for expanding this technology to high-density large area transparent arrays to monitor brain-scale cortical activity in large animal models or humans.

“Our technology is also well-suited for neurovascular and neurometabolic studies, providing a ‘gold standard’ neuronal correlate for optical measurements of vascular, hemodynamic, and metabolic activity,” Kuzum points out. “It will find application in multiple areas, advancing our understanding of how microscopic neural activity at the cellular scale translates into macroscopic activity of large neuron populations.”

“Combining optical techniques with electrical recordings using graphene electrodes will allow to connect the large body of neuroscience knowledge obtained from animal models to human studies mainly relying on electrophysiological recordings of brain-scale activity,” she adds.

Next steps for the team involve employing this technology to investigate coupling and information transfer between different brain regions.

This work is part of the US BRAIN (Brain Research through Advancing Innovative Neurotechnologies) initiative and there’s more than one team working with transparent graphene electrodes. John Hewitt in an Oct. 21, 2014 posting on ExtremeTech describes two other teams’ work (Note: Links have been removed),

The solution [to the problems with metal electrodes], now emerging from multiple labs throughout the universe is to build flexible, transparent electrode arrays from graphene. Two studies in the latest issue of Nature Communications, one from the University of Wisconsin-Madison and the other from Penn [University of Pennsylvania], describe how to build these devices.

The University of Wisconsin researchers are either a little bit smarter or just a little bit richer, because they published their work open access. It’s a no-brainer then that we will focus on their methods first, and also in more detail. To make the arrays, these guys first deposited the parylene (polymer) substrate on a silicon wafer, metalized it with gold, and then patterned it with an electron beam to create small contact pads. The magic was to then apply four stacked single-atom-thick graphene layers using a wet transfer technique. These layers were then protected with a silicon dioxide layer, another parylene layer, and finally molded into brain signal recording goodness with reactive ion etching.

PennTransparentelectrodeThe researchers went with four graphene layers because that provided optimal mechanical integrity and conductivity while maintaining sufficient transparency. They tested the device in opto-enhanced mice whose neurons expressed proteins that react to blue light. When they hit the neurons with a laser fired in through the implant, the protein channels opened and fired the cell beneath. The masterstroke that remained was then to successfully record the electrical signals from this firing, sit back, and wait for the Nobel prize office to call.

The Penn State group [Note: Every reearcher mentioned in the paper Hewitt linked to is from the University of Pennsylvania] in the  used a similar 16-spot electrode array (pictured above right), and proceeded — we presume — in much the same fashion. Their angle was to perform high-resolution optical imaging, in particular calcium imaging, right out through the transparent electrode arrays which simultaneously recorded in high-temporal-resolution signals. They did this in slices of the hippocampus where they could bring to bear the complex and multifarious hardware needed to perform confocal and two-photon microscopy. These latter techniques provide a boost in spatial resolution by zeroing in over narrow planes inside the specimen, and limiting the background by the requirement of two photons to generate an optical signal. We should mention that there are voltage sensitive dyes available, in addition to standard calcium dyes, which can almost record the fastest single spikes, but electrical recording still reigns supreme for speed.

What a mouse looks like with an optogenetics system plugged in

What a mouse looks like with an optogenetics system plugged in

One concern of both groups in making these kinds of simultaneous electro-optic measurements was the generation of light-induced artifacts in the electrical recordings. This potential complication, called the Becqueral photovoltaic effect, has been known to exist since it was first demonstrated back in 1839. When light hits a conventional metal electrode, a photoelectrochemical (or more simply, a photovoltaic) effect occurs. If present in these recordings, the different signals could be highly disambiguatable. The Penn researchers reported that they saw no significant artifact, while the Wisconsin researchers saw some small effects with their device. In particular, when compared with platinum electrodes put into the opposite side cortical hemisphere, the Wisconsin researchers found that the artifact from graphene was similar to that obtained from platinum electrodes.

Here’s a link to and a citation for the latest research from UCSD,

Deep 2-photon imaging and artifact-free optogenetics through transparent graphene microelectrode arrays by Martin Thunemann, Yichen Lu, Xin Liu, Kıvılcım Kılıç, Michèle Desjardins, Matthieu Vandenberghe, Sanaz Sadegh, Payam A. Saisan, Qun Cheng, Kimberly L. Weldy, Hongming Lyu, Srdjan Djurovic, Ole A. Andreassen, Anders M. Dale, Anna Devor, & Duygu Kuzum. Nature Communicationsvolume 9, Article number: 2035 (2018) doi:10.1038/s41467-018-04457-5 Published: 23 May 2018

This paper is open access.

You can find out more about the US BRAIN initiative here and if you’re curious, you can find out more about the project at UCSD here. Duygu Kuzum (now at UCSD) was at  the University of Pennsylvania in 2014 and participated in the work mentioned in Hewitt’s 2014 posting.

US Dept. of Agriculture announces its nanotechnology research grants

I don’t always stumble across the US Department of Agriculture’s nanotechnology research grant announcements but I’m always grateful when I do as it’s good to find out about  nanotechnology research taking place in the agricultural sector. From a July 21, 2017 news item on Nanowerk,,

The U.S. Department of Agriculture’s (USDA) National Institute of Food and Agriculture (NIFA) today announced 13 grants totaling $4.6 million for research on the next generation of agricultural technologies and systems to meet the growing demand for food, fuel, and fiber. The grants are funded through NIFA’s Agriculture and Food Research Initiative (AFRI), authorized by the 2014 Farm Bill.

“Nanotechnology is being rapidly implemented in medicine, electronics, energy, and biotechnology, and it has huge potential to enhance the agricultural sector,” said NIFA Director Sonny Ramaswamy. “NIFA research investments can help spur nanotechnology-based improvements to ensure global nutritional security and prosperity in rural communities.”

A July 20, 2017 USDA news release, which originated the news item, lists this year’s grants and provides a brief description of a few of the newly and previously funded projects,

Fiscal year 2016 grants being announced include:

Nanotechnology for Agricultural and Food Systems

  • Kansas State University, Manhattan, Kansas, $450,200
  • Wichita State University, Wichita, Kansas, $340,000
  • University of Massachusetts, Amherst, Massachusetts, $444,550
  • University of Nevada, Las Vegas, Nevada,$150,000
  • North Dakota State University, Fargo, North Dakota, $149,000
  • Cornell University, Ithaca, New York, $455,000
  • Cornell University, Ithaca, New York, $450,200
  • Oregon State University, Corvallis, Oregon, $402,550
  • University of Pennsylvania, Philadelphia, Pennsylvania, $405,055
  • Gordon Research Conferences, West Kingston, Rhode Island, $45,000
  • The University of Tennessee,  Knoxville, Tennessee, $450,200
  • Utah State University, Logan, Utah, $450,200
  • The George Washington University, Washington, D.C., $450,200

Project details can be found at the NIFA website (link is external).

Among the grants, a University of Pennsylvania project will engineer cellulose nanomaterials [emphasis mine] with high toughness for potential use in building materials, automotive components, and consumer products. A University of Nevada-Las Vegas project will develop a rapid, sensitive test to detect Salmonella typhimurium to enhance food supply safety.

Previously funded grants include an Iowa State University project in which a low-cost and disposable biosensor made out of nanoparticle graphene that can detect pesticides in soil was developed. The biosensor also has the potential for use in the biomedical, environmental, and food safety fields. University of Minnesota (link is external) researchers created a sponge that uses nanotechnology to quickly absorb mercury, as well as bacterial and fungal microbes from polluted water. The sponge can be used on tap water, industrial wastewater, and in lakes. It converts contaminants into nontoxic waste that can be disposed in a landfill.

NIFA invests in and advances agricultural research, education, and extension and promotes transformative discoveries that solve societal challenges. NIFA support for the best and brightest scientists and extension personnel has resulted in user-inspired, groundbreaking discoveries that combat childhood obesity, improve and sustain rural economic growth, address water availability issues, increase food production, find new sources of energy, mitigate climate variability and ensure food safety. To learn more about NIFA’s impact on agricultural science, visit www.nifa.usda.gov/impacts, sign up for email updates (link is external) or follow us on Twitter @USDA_NIFA (link is external), #NIFAImpacts (link is external).

Given my interest in nanocellulose materials (Canada was/is a leader in the production of cellulose nanocrystals [CNC] but there has been little news about Canadian research into CNC applications), I used the NIFA link to access the table listing the grants and clicked on ‘brief’ in the View column in the University of Pennsylania row to find this description of the project,

ENGINEERING CELLULOSE NANOMATERIALS WITH HIGH TOUGHNESS

NON-TECHNICAL SUMMARY: Cellulose nanofibrils (CNFs) are natural materials with exceptional mechanical properties that can be obtained from renewable plant-based resources. CNFs are stiff, strong, and lightweight, thus they are ideal for use in structural materials. In particular, there is a significant opportunity to use CNFs to realize polymer composites with improved toughness and resistance to fracture. The overall goal of this project is to establish an understanding of fracture toughness enhancement in polymer composites reinforced with CNFs. A key outcome of this work will be process – structure – fracture property relationships for CNF-reinforced composites. The knowledge developed in this project will enable a new class of tough CNF-reinforced composite materials with applications in areas such as building materials, automotive components, and consumer products.The composite materials that will be investigated are at the convergence of nanotechnology and bio-sourced material trends. Emerging nanocellulose technologies have the potential to move biomass materials into high value-added applications and entirely new markets.

It’s not the only nanocellulose material project being funded in this round, there’s this at North Dakota State University, from the NIFA ‘brief’ project description page,

NOVEL NANOCELLULOSE BASED FIRE RETARDANT FOR POLYMER COMPOSITES

NON-TECHNICAL SUMMARY: Synthetic polymers are quite vulnerable to fire.There are 2.4 million reported fires, resulting in 7.8 billion dollars of direct property loss, an estimated 30 billion dollars of indirect loss, 29,000 civilian injuries, 101,000 firefighter injuries and 6000 civilian fatalities annually in the U.S. There is an urgent need for a safe, potent, and reliable fire retardant (FR) system that can be used in commodity polymers to reduce their flammability and protect lives and properties. The goal of this project is to develop a novel, safe and biobased FR system using agricultural and woody biomass. The project is divided into three major tasks. The first is to manufacture zinc oxide (ZnO) coated cellulose nanoparticles and evaluate their morphological, chemical, structural and thermal characteristics. The second task will be to design and manufacture polymer composites containing nano sized zinc oxide and cellulose crystals. Finally the third task will be to test the fire retardancy and mechanical properties of the composites. Wbelieve that presence of zinc oxide and cellulose nanocrystals in polymers will limit the oxygen supply by charring, shielding the surface and cellulose nanocrystals will make composites strong. The outcome of this project will help in developing a safe, reliable and biobased fire retardant for consumer goods, automotive, building products and will help in saving human lives and property damage due to fire.

One day, I hope to hear about Canadian research into applications for nanocellulose materials. (fingers crossed for good luck)

Curiosity may not kill the cat but, in science, it might be an antidote to partisanship

I haven’t stumbled across anything from the Cultural Cognition Project at Yale Law School in years so before moving onto their latest news, here’s more about the project,

The Cultural Cognition Project is a group of scholars interested in studying how cultural values shape public risk perceptions and related policy beliefs. Cultural cognition refers to the tendency of individuals to conform their beliefs about disputed matters of fact (e.g., whether global warming is a serious threat; whether the death penalty deters murder; whether gun control makes society more safe or less) to values that define their cultural identities.Project members are using the methods of various disciplines — including social psychology, anthropology, communications, and political science — to chart the impact of this phenomenon and to identify the mechanisms through which it operates. The Project also has an explicit normative objective: to identify processes of democratic decisionmaking by which society can resolve culturally grounded differences in belief in a manner that is both congenial to persons of diverse cultural outlooks and consistent with sound public policymaking.

It’s nice to catch up with some of the project’s latest work, from a Jan. 26, 2017 Yale University news release (also on EurekAlert),

Disputes over science-related policy issues such as climate change or fracking often seem as intractable as other politically charged debates. But in science, at least, simple curiosity might help bridge that partisan divide, according to new research.

In a study slated for publication in the journal Advances in Political Psychology, a Yale-led research team found that people who are curious about science are less polarized in their views on contentious issues than less-curious peers.

In an experiment, they found out why: Science-curious individuals are more willing to engage with surprising information that runs counter to their political predispositions.

“It’s a well-established finding that most people prefer to read or otherwise be exposed to information that fits rather than challenges their political preconceptions,” said research team leader Dan Kahan, Elizabeth K. Dollard Professor of Law and professor of psychology at Yale Law School. “This is called the echo-chamber effect.”

But science-curious individuals are more likely to venture out of that chamber, he said.

“When they are offered the choice to read news articles that support their views or challenge them on the basis of new evidence, science-curious individuals opt for the challenging information,” Kahan said. “For them, surprising pieces of evidence are bright shiny objects — they can’t help but grab at them.”

Kahan and other social scientists previously have shown that information based on scientific evidence can actually intensify — rather than moderate — political polarization on contentious topics such as gun control, climate change, fracking, or the safety of certain vaccines. The new study, which assessed science knowledge among subjects, reiterates the gaping divide separating how conservatives and liberals view science.

Republicans and Democrats with limited knowledge of science were equally likely to agree or disagree with the statement that “there is solid evidence that global warming is caused by human activity. However, the most science-literate conservatives were much more likely to disagree with the statement than less-knowledgeable peers. The most knowledgeable liberals almost universally agreed with the statement.

“Whatever measure of critical reasoning we used, we always observed this depressing pattern: The members of the public most able to make sense of scientific evidence are in fact the most polarized,” Kahan said.

But knowledge of science, and curiosity about science, are not the same thing, the study shows.

The team became interested in curiosity because of its ongoing collaborative research project to improve public engagement with science documentaries involving the Cultural Cognition Project at Yale Law School, the Annenberg Public Policy Center of the University of Pennsylvania, and Tangled Bank Studios at the Howard Hughes Medical Institute.

They noticed that the curious — those who sought out science stories for personal pleasure — not only were more interested in viewing science films on a variety of topics but also did not display political polarization associated with contentious science issues.

The new study found, for instance, that a much higher percentage of curious liberals and conservatives chose to read stories that ran counter to their political beliefs than did their non-curious peers.

“As their science curiosity goes up, the polarizing effects of higher science comprehension dissipate, and people move the same direction on contentious policies like climate change and fracking,” Kahan said.

It is unclear whether curiosity applied to other controversial issues can minimize the partisan rancor that infects other areas of society. But Kahan believes that the curious from both sides of the political and cultural divide should make good ambassadors to the more doctrinaire members of their own groups.

“Politically curious people are a resource who can promote enlightened self-government by sharing scientific information they are naturally inclined to learn and share,” he said.

Here’s my standard link to and citation for the paper,

Science Curiosity and Political Information Processing by Dan M. Kahan, Asheley R Landrum, Katie Carpenter, Laura Helft, and Kathleen Hall Jamieson. Political Psychology Volume 38, Issue Supplement S1 February 2017 Pages 179–199 DOI: 10.1111/pops.12396View First published: 26 January 2017

This paper is open and it can also be accessed here.

I last mentioned Kahan and The Cultural Cognition Project in an April 10, 2014 posting (scroll down about 45% of the way) about responsible science.

Nanoparticles for breaking up plaque and preventing cavities

There may be iron in your tooth care future if a team of researchers at the University of Pennsylvania have their way. From a July 26, 2016 news item on ScienceDaily,

The bacteria that live in dental plaque and contribute to tooth decay often resist traditional antimicrobial treatment, as they can “hide” within a sticky biofilm matrix, a glue-like polymer scaffold.

A new strategy conceived by University of Pennsylvania researchers took a more sophisticated approach. Instead of simply applying an antibiotic to the teeth, they took advantage of the pH-sensitive and enzyme-like properties of iron-containing nanoparticles to catalyze the activity of hydrogen peroxide, a commonly used natural antiseptic. The activated hydrogen peroxide produced free radicals that were able to simultaneously degrade the biofilm matrix and kill the bacteria within, significantly reducing plaque and preventing the tooth decay, or cavities, in an animal model.

“Even using a very low concentration of hydrogen peroxide, the process was incredibly effective at disrupting the biofilm,” said Hyun (Michel) Koo, a professor in the Penn School of Dental Medicine’s Department of Orthodontics and divisions of Pediatric Dentistry and Community and Oral Health and the senior author of the study, which was published in the journal Biomaterials. “Adding nanoparticles increased the efficiency of bacterial killing more than 5,000-fold.”

A July 25, 2016 University of Pennsylvania news release, which originated the news item, describes the genesis of the work and provides more details about the current research (Note: A link has been removed),

The work built off a seminal finding by Gao [Lizeng Gao, a postdoctoral researcher in Koo’s lab] and colleagues, published in 2007 in Nature Nanotechnology, showing that nanoparticles, long believed to be biologically and chemically inert, could in fact possess enzyme-like properties. In that study, Gao showed that an iron oxide nanoparticle behaved similarly to a peroxidase, an enzyme found naturally that catalyzes oxidative reactions, often using hydrogen peroxide.

When Gao joined Koo’s lab in 2013, he proposed using these nanoparticles in an oral setting, as the oxidation of hydrogen peroxide produces free radicals that can kill bacteria.

“When he first presented it to me, I was very skeptical,” Koo said, “because these free radicals can also damage healthy tissue. But then he refuted that and told me this is different because the nanoparticles’ activity is dependent on pH.”

Gao had found that the nanoparticles had no catalytic activity at neutral or near-neutral pH of 6.5 or 7, physiological values typically found in blood or in a healthy mouth. But when pH was acidic, closer to 5, they become highly active and can rapidly produce free radicals.

The scenario was ideal for targeting plaque, which can produce an acidic microenvironment when exposed to sugars.

Gao and Koo reached out to Cormode [David Cormode, an assistant professor of radiology and bioengineering], who had experience working with iron oxide nanoparticles in a radiological imaging context, to help them synthesize, characterize and test the effectiveness of the nanoparticles, several forms of which are already FDA-approved for imaging in humans.

Beginning with in vitro studies, which involved growing a biofilm containing the cavity-causing bacteria Streptococcus mutans on a tooth-enamel-like surface and then exposing it to sugar, the researchers confirmed that the nanoparticles adhered to the biofilm, were retained even after treatment stopped and could effectively catalyze hydrogen peroxide in acidic conditions.

They also showed that the nanoparticles’ reaction with a 1 percent or less hydrogen peroxide solution was remarkably effective at killing bacteria, wiping out more than 99.9 percent of the S. mutans in the biofilm within five minutes, an efficacy more than 5,000 times greater than using hydrogen peroxide alone. Even more promising, they demonstrated that the treatment regimen, involving a 30-second topical treatment of the nanoparticles followed by a 30-second treatment with hydrogen peroxide, could break down the biofilm matrix components, essentially removing the protective sticky scaffold.

Moving to an animal model, they applied the nanoparticles and hydrogen peroxide topically to the teeth of rats, which can develop tooth decay when infected with S. mutans just as humans do. Twice-a-day, one-minute treatments for three weeks significantly reduced the onset and severity of carious lesions, the clinical term for tooth decay, compared to the control or treatment with hydrogen peroxide alone. The researchers observed no adverse effects on the gum or oral soft tissues from the treatment.

“It’s very promising,” said Koo. “The efficacy and toxicity need to be validated in clinical studies, but I think the potential is there.”

Among the attractive features of the platform is the fact that the components are relatively inexpensive.

“If you look at the amount you would need for a dose, you’re looking at something like 5 milligrams,” Cormode said. “It’s a tiny amount of material, and the nanoparticles are fairly easily synthesize, so we’re talking about a cost of cents per dose.”

In addition, the platform uses a concentration of hydrogen peroxide, 1 percent, which is lower than many currently available tooth-whitening systems that use 3 to 10 percent concentrations, minimizing the chance of negative side effects.

Looking ahead, Gao, Koo, Cormode and colleagues hope to continue refining and improving upon the effectiveness of the nanoparticle platform to fight biofilms.

“We’re studying the role of nanoparticle coatings, composition, size and so forth so we can engineer the particles for even better performance,” Cormode said.

The funding agencies provide a note of interest (Note: Links have been removed),

The study was funded by the International Association for Dental Research/GlaxoSmithKline Innovation in Oral Health Award, National Science Foundation and University of Pennsylvania Research Foundation.

Presumably the industry as represented by the GlaxoSmithKline Innovation in Oral Health Award is keeping a close eye on this work.

Here’s a link to and a citation for the paper,

Nanocatalysts promote Streptococcus mutans biofilm matrix degradation and enhance bacterial killing to suppress dental caries in vivo by Lizeng Gao, Yuan Liu, Dongyeop Kim, Yong Li, Geelsu Hwang, Pratap C. Naha, David P. Cormode, & Hyun Koo. Biomaterials Volume 101, September 2016, Pages 272–284 doi:10.1016/j.biomaterials.2016.05.051

This paper is behind a paywall.

Placenta-on-a-chip for research into causes for preterm birth

Preterm birth (premature baby) research has received a boost with this latest work from the University of Pennsylvania. A July 21, 2016 news item on phys.org tells us more,

Researchers at the University of Pennsylvania have developed the first placenta-on-a-chip that can fully model the transport of nutrients across the placental barrier.

A July 21, 2016 University of Pennsylvania news release, which originated the news item, provides more detail about the chip and the research (Note: Links have been removed),

The flash-drive-sized device contains two layers of human cells that model the interface between mother and fetus. Microfluidic channels on either side of those layers allow researchers to study how molecules are transported through, or are blocked by, that interface.

Like other organs-on-chips, such as ones developed to simulate lungs, intestines and eyes, the placenta-on-a-chip provides a unique capability to mimic and study the function of that human organ in ways that have not been possible using traditional tools.

Research on the team’s placenta-on-a-chip is part of a nationwide effort sponsored by the March of Dimes to identify causes of preterm birth and ways to prevent it. Prematurely born babies may experience lifelong, debilitating consequences, but the underlying mechanisms of this condition are not well understood due in part to the difficulties of experimenting with intact, living human placentae.

The research was led by Dan Huh, the Wilf Family Term Assistant Professor of Bioengineering in Penn’s School of Engineering and Applied Science, and Cassidy Blundell, a graduate student in the Huh lab. They collaborated with Samuel Parry, the Franklin Payne Professor of Obstetrics and Gynecology; Christos Coutifaris, the Nancy and Richard Wolfson Professor of Obstetrics and Gynecology in Penn’s Perelman School of Medicine; and Emily Su, assistant professor of obstetrics and gynecology in the Anschutz Medical School of the University of Colorado Denver.

The researchers’ placenta-on-a-chip is a clear silicone device with two parallel microfluidic channels separated by a porous membrane. On one side of those pores, trophoblast cells, which are found at the placental interface with maternal blood, are grown. On the other side are endothelial cells, found on the interior of fetal blood vessels. The layers of those two cell types mimic the placental barrier, the gatekeeper between the maternal and fetal circulatory systems.

“That barrier,” Blundell said, “mediates all transport between mother and fetus during pregnancy. Nutrients, but also foreign agents like viruses, need to be either transported by that barrier or stopped.”

“One of the most important function of the placental barrier is transport,” Huh said, “so it’s essential for us to mimic that functionality.”

In 2013, Huh and his collaborators at Seoul National University conducted a preliminary study to create a microfluidic device for culturing trophoblast cells and fetal endothelial cells. This model, however, lacked the ability to form physiological placental tissue and accurately simulate transport function of the placental barrier.

In their new study, the Penn researchers have demonstrated that the two layers of cells continue to grow and develop while inside the chip, undergoing a process known as “syncytialization.”

“The placental cells change over the course of pregnancy,” Huh said. “During pregnancy, the placental trophoblast cells actually fuse with one another to form an interesting tissue called syncytium. The barrier also becomes thinner as the pregnancy progresses, and with our new model we’re able to reproduce this change.

“This process is very important because it affects placental transport and was a critical aspect not represented in our previous model.”

The Penn team validated the new model by showing glucose transfer rates across this syncytialized barrier matched those measured in perfusion studies of donated human placentae.

While useful in providing this type of baseline, donated placental tissue can be problematic for doing many of the types of studies necessary for fully understanding the structure and function of the placenta, especially as it pertains to diseases and disorders.

“The placenta is arguably the least understood organ in the human body,” Huh said, “and much remains to be learned about how transport between mother and fetus works at the tissue, cellular and molecular levels. An isolated whole organ is an not ideal platform for these types of mechanistic studies.”

“Beyond the scarcity of samples,” Blundell said, “there’s a limited lifespan of how long the tissue remains viable, for only a few hours after delivery, and the system that is used to perfuse the tissue and perform transport studies is complex.”

While the placenta-on-a-chip is still in the early stages of testing, researchers at Penn and beyond are already planning to use it in studies on preterm birth.

“This effort,” Parry said, “was part of the much larger Prematurity Research Center here at Penn, one of five centers around the country funded by the March of Dimes to study the causes of preterm birth. The rate of preterm birth is about 10 to 11 percent of all pregnancies. That rate has not been decreasing, and interventions to prevent preterm birth have been largely unsuccessful.”

As part of a $10 million grant from the March of Dimes that established the Center, Parry and his colleagues research metabolic changes that may be associated with preterm birth using in vitro placental cell lines and ex vivo placental tissue. The grant also supported their work with the Huh lab to develop new tools that could model preterm birth-associated placental dysfunction and inform such research efforts.

“Since publishing this paper,” Samuel Parry said, “we’ve reached out to the principal investigators at the other four March of Dimes sites and offered to provide them this model to use in their experiments.”

“Eventually,” Huh said, “we hope to leverage the unique capabilities of our model to demonstrate the potential of organ-on-a-chip technology as a new strategy to innovate basic and translational research in reproductive biology and medicine.”

Here’s a link to and a citation for the paper,

A microphysiological model of the human placental barrier by Cassidy Blundell, Emily R. Tess, Ariana S. R. Schanzer, Christos Coutifaris, Emily J. Su, Samuel Parry. and Dongeun Huh. Lab Chip, 2016, Advance Article DOI: 10.1039/C6LC00259E First published online 20 May 2016

I believe this paper is behind a paywall.

One final note, I thought this was a really well written news release.

A freestanding plate of nanoscale thickness big enough to be ‘hand’led

A rather remarkable achievement is mentioned in a Dec. 3, 2015 news item on Nanotechnology Now,

Researchers at the University of Pennsylvania have now created the thinnest plates that can be picked up and manipulated by hand.

Despite being thousands of times thinner than a sheet of paper and hundreds of times thinner than household cling wrap or aluminum foil, their corrugated plates of aluminum oxide spring back to their original shape after being bent and twisted.

Like cling wrap, comparably thin materials immediately curl up on themselves and get stuck in deformed shapes if they are not stretched on a frame or backed by another material.

Being able to stay in shape without additional support would allow this material, and others designed on its principles, to be used in aviation and other structural applications where low weight is at a premium.

Here’s an image provided by the researchers,

Caption: Even though they are less than 100 nanometers thick, the researchers' plates are strong enough to be picked up by hand and retain their shape after being bent and squeezed. Credit: University of Pennsylvania

Caption: Even though they are less than 100 nanometers thick, the researchers’ plates are strong enough to be picked up by hand and retain their shape after being bent and squeezed. Credit: University of Pennsylvania

A Dec. 3, 2015 University of Pennsylvania news release (also on EurekAlert), which originated the news item, provides more detail,

“Materials on the nanoscale are often much stronger than you’d expect, but they can be hard to use on the macroscale” Bargatin [Igor Bargatin, Assistant Professor] said. “We’ve essentially created a freestanding plate that has nanoscale thickness but is big enough to be handled by hand. That hasn’t been done before.”

Graphene, which can be as thin as a single atom of carbon, has been the poster-child for ultra-thin materials since it’s discovery won the Nobel Prize in Physics in 2010. Graphene is prized for its electrical properties, but its mechanical strength is also very appealing, especially if it could stand on its own. However, graphene and other atomically thin films typically need to be stretched like a canvas in a frame, or even mounted on a backing, to prevent them from curling or clumping up on their own.

“The problem is that frames are heavy, making it impossible to use the intrinsically low weight of these ultra-thin films,” Bargatin said. “Our idea was to use corrugation instead of a frame. That means the structures we make are no longer completely planar, instead, they have a three-dimensional shape that looks like a honeycomb, but they are flat and contiguous and completely freestanding.”

“It’s like an egg carton, but on the nanoscale,” said Purohit. [Prashant Purohit, associate professor]

The researchers’ plates are between 25 and 100 nanometers thick and are made of aluminum oxide, which is deposited one atomic layer at a time to achieve precise control of thickness and their distinctive honeycomb shape.

“Aluminum oxide is actually a ceramic, so something that is ordinarily pretty brittle,” Bargatin said. “You would expect it, from daily experience, to crack very easily. But the plates bend, twist, deform and recover their shape in such a way that you would think they are made out of plastic. The first time we saw it, I could hardly believe it.”

Once finished, the plates’ corrugation provides enhanced stiffness. When held from one end, similarly thin films would readily bend or sag, while the honeycomb plates remain rigid. This guards against the common flaw in un-patterned thin films, where they curl up on themselves.

This ease of deformation is tied to another behavior that makes ultra-thin films hard to use outside controlled conditions: they have the tendency to conform to the shape of any surface and stick to it due to Van der Waals forces. Once stuck, they are hard to remove without damaging them.

Totally flat films are also particularly susceptible to tears or cracks, which can quickly propagate across the entire material.

“If a crack appears in our plates, however, it doesn’t go all the way through the structure,” Davami [Keivan Davami, postdoctoral scholar] said. “It usually stops when it gets to one of the vertical walls of the corrugation.”

The corrugated pattern of the plates is an example of a relatively new field of research: mechanical metamaterials. Like their electromagnetic counterparts, mechanical metamaterials achieve otherwise impossible properties from the careful arrangement of nanoscale features. In mechanical metamaterials’ case, these properties are things like stiffness and strength, rather than their ability to manipulate electromagnetic waves.

Other existing examples of mechanical metamaterials include “nanotrusses,” which are exceptionally lightweight and robust three-dimensional scaffolds made out of nanoscale tubes. The Penn researchers’ plates take the concept of mechanical metamaterials a step further, using corrugation to achieve similar robustness in a plate form and without the holes found in lattice structures.

That combination of traits could be used to make wings for insect-inspired flying robots, or in other applications where the combination of ultra-low thickness and mechanical robustness is critical.

“The wings of insects are a few microns thick, and can’t thinner because they’re made of cells,” Bargatin said. “The thinnest man-made wing material I know of is made by depositing a Mylar film on a frame, and it’s about half a micron thick. Our plates can be ten or more times thinner than that, and don’t need a frame at all. As a result, they weigh as little as than a tenth of a gram per square meter.”

Here’s a link to and a citation for the paper,

Ultralight shape-recovering plate mechanical metamaterials by Keivan Davami, Lin Zhao, Eric Lu, John Cortes, Chen Lin, Drew E. Lilley, Prashant K. Purohit, & Igor Bargatin. Nature Communications 6, Article number: 10019 doi:10.1038/ncomms10019 Published 03 December 2015

This is an open access paper,