Tag Archives: University of Tennessee Knoxville

Dynamic magnetic fractal networks for neuromorphic (brainlike) computing

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Credit: Advanced Materials (2023). DOI: 10.1002/adma.202300416 [cover image]

This is a different approach to neuromorphic (brainlike) computing being described in an August 28, 2023 news item on phys.org, Note: A link has been removed,

The word “fractals” might inspire images of psychedelic colors spiraling into infinity in a computer animation. An invisible, but powerful and useful, version of this phenomenon exists in the realm of dynamic magnetic fractal networks.

Dustin Gilbert, assistant professor in the Department of Materials Science and Engineering [University of Tennessee, US], and colleagues have published new findings in the behavior of these networks—observations that could advance neuromorphic computing capabilities.

Their research is detailed in their article “Skyrmion-Excited Spin-Wave Fractal Networks,” cover story for the August 17, 2023, issue of Advanced Materials.

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An August 18, 2023 University of Tennessee news release, which originated the news item, provides more details,

“Most magnetic materials—like in refrigerator magnets—are just comprised of domains where the magnetic spins all orient parallel,” said Gilbert. “Almost 15 years ago, a German research group discovered these special magnets where the spins make loops—like a nanoscale magnetic lasso. These are called skyrmions.”

Named for legendary particle physicist Tony Skyrme, a skyrmion’s magnetic swirl gives it a non-trivial topology. As a result of this topology, the skyrmion has particle-like properties—they are hard to create or destroy, they can move and even bounce off of each other. The skyrmion also has dynamic modes—they can wiggle, shake, stretch, whirl, and breath[e].

As the skyrmions “jump and jive,” they are creating magnetic spin waves with a very narrow wavelength. The interactions of these waves form an unexpected fractal structure.

“Just like a person dancing in a pool of water, they generate waves which ripple outward,” said Gilbert. “Many people dancing make many waves, which normally would seem like a turbulent, chaotic sea. We measured these waves and showed that they have a well-defined structure and collectively form a fractal which changes trillions of times per second.”

Fractals are important and interesting because they are inherently tied to a “chaos effect”—small changes in initial conditions lead to big changes in the fractal network.

“Where we want to go with this is that if you have a skyrmion lattice and you illuminate it with spin waves, the way the waves make its way through this fractal-generating structure is going to depend very intimately on its construction,” said Gilbert. “So, if you could write individual skyrmions, it can effectively process incoming spin waves into something on the backside—and it’s programmable. It’s a neuromorphic architecture.”

The Advanced Materials cover illustration [image at top of this posting] depicts a visual representation of this process, with the skyrmions floating on top of a turbulent blue sea illustrative of the chaotic structure generated by the spin wave fractal.

“Those waves interfere just like if you throw a handful of pebbles into a pond,” said Gilbert. “You get a choppy, turbulent mess. But it’s not just any simple mess, it’s actually a fractal. We have an experiment now showing that the spin waves generated by skyrmions aren’t just a mess of waves, they have inherent structure of their very own. By, essentially, controlling those stones that we ‘throw in,’ you get very different patterns, and that’s what we’re driving towards.”

The discovery was made in part by neutron scattering experiments at the Oak Ridge National Laboratory (ORNL) High Flux Isotope Reactor and at the National Institute of Standards and Technology (NIST) Center for Neutron Research. Neutrons are magnetic and pass through materials easily, making them ideal probes for studying materials with complex magnetic behavior such as skyrmions and other quantum phenomena.

Gilbert’s co-authors for the new article are Nan Tang, Namila Liyanage, and Liz Quigley, students in his research group; Alex Grutter and Julie Borchers from National Institute of Standards and Technology (NIST), Lisa DeBeer-Schmidt and Mike Fitzsimmons from Oak Ridge National Laboratory; and Eric Fullerton, Sheena Patel, and Sergio Montoya from the University of California, San Diego.

The team’s next step is to build a working model using the skyrmion behavior.

“If we can develop thinking computers, that, of course, is extraordinarily important,” said Gilbert. “So, we will propose to make a miniaturized, spin wave neuromorphic architecture.” He also hopes that the ripples from this UT Knoxville discovery inspire researchers to explore uses for a spiraling range of future applications.

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

Skyrmion-Excited Spin-Wave Fractal Networks by Nan Tang, W. L. N. C. Liyanage, Sergio A. Montoya, Sheena Patel, Lizabeth J. Quigley, Alexander J. Grutter, Michael R. Fitzsimmons, Sunil Sinha, Julie A. Borchers, Eric E. Fullerton, Lisa DeBeer-Schmitt, Dustin A. Gilbert. Advanced Materials Volume 35, Issue 33 August 17, 2023 2300416 DOI: https://doi.org/10.1002/adma.202300416 First published: 04 May 2023

This paper is behind a paywall.

Flesh-eating fungus, ivy and other inspirations from nature

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Michael Berger has featured Dr. Mingjun Zhang’s team’s fascinating work on flesh-eating fungus in a Dec. 18, 2012 Spotlight article on Nanowerk,

“Most studies on naturally occurring organic nanoparticles have focused on higher organisms,” Mingjun Zhang, an associate professor of biomedical engineering at the University of Tennessee, Knoxville, tells Nanowerk. “Given the earth’s rich biological diversity, it is reasonable to hypothesize that naturally occurring nanoparticles, of various forms and functions, may be produced by a wide range of organisms from microbes to metazoans.”

In his research, Zhang has focused on looking at nature for inspirations for solutions to challenges in engineering and medicine, especially in small-scale, such as bioinspired nanomaterials, bioinspired energy-efficient propulsive systems, and bioinspired nanobio systems for interfacing with cellular systems.

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In new work, Zhang and his research associate Dr. Yongzhong Wang have turned their focus to Arthrobotrys oligospora, a representative flesh eater with a predatory life stage in the fungal kingdom.

The researchers have published their work in Advanced Functional Materials ((early online publication behind a paywall),

Naturally Occurring Nanoparticles from Arthrobotrys oligospora as a Potential Immunostimulatory and Antitumor Agent by Yongzhong Wang, Leming Sun, Sijia Yi, Yujian Huang, Scott C. Lenaghan, and Mingjun Zhang in Advanced Functional Materials

Article first published online: 4 DEC 2012 DOI: 10.1002/adfm.201202619

Here’s the abstract,

Arthrobotrys oligospora, a representative flesh eater in the fungal kingdom, is a potential source for natural-based biomaterials due to the presence of specialized 3D adhesive traps that can capture, penetrate, and digest free-living nematodes in diverse environments. The purpose of this study is to discover novel nanoparticles that occur naturally in A. oligospora and to exploit its potential biomedical applications. A new culture method, fungal sitting drop culture method, is established in order to monitor the growth of A. oligospora in situ, and observe the nanoparticle production without interfering or contamination from the solid media. Abundant spherical nanoparticles secreted from the fungus are first revealed by scanning electron microscopy and atomic force microscopy. They have an average size of 360–370 nm, with a zeta potential of –33 mV at pH 6.0. Further analyses reveal that there is ≈28 μg of glycosaminoglycan and ≈550 μg of protein per mg of nanoparticles. Interestingly, the nanoparticles significantly induce TNF-α secretion in RAW264.7mouse macrophages, indicating a potential immunostimulatory effect. The nanoparticles themselves are also found slightly cytotoxic to mouse melanoma B16BL6 and human lung cancer A549 cells, and show a synergistic cytotoxic effect upon conjugation with doxorubicin against both cells. This study proposes a new approach for producing novel organic nanoparticles secreted from microorganisms under controlled conditions. The findings here also highlight the potential roles of the naturally occurring nanoparticles from A. oligospora as an immunostimulatory and antitumor agent for cancer immunochemotherapy.

In more generalized language (from Berger’s Spotlight article),

“It is really exciting to use a natural microbe system to produce nanoparticles for potential cancer therapy,” says Zhang. “Originally, we were trying to understand how the fungus secretes an adhesive trap that can capture, penetrate, and digest free-living nematodes in diverse environments. By doing that we almost accidentally discovered the nanoparticles produced.”

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Zhang’s team investigated the fungal nanoparticles’ potential as a stimulant for the immune system, and found through an in vitro study that the nanoparticles activate secretion of an immune-system stimulant within a white blood cell line. They also investigated the nanoparticles’ potential as an antitumor agent by testing in vitro the toxicity to cells using two tumor cell lines, and discovered nanoparticles do kill cancer cells.

Berger’s article in addition to giving more details about Zhang’s current work and his work with ivy and possible applications for ivy-based nanoparticles in sunscreens also provides some discussion of naturally occurring nanoparticles as opposed to engineered (or man-made)  nanoparticles.

The University of Tennessee’s Dec. 4, 2012 press release is also a good source of information on Zhang’s latest work on flesh-eating fungus. For the indefatiguable who are interested in Zhang’s work on ivy and potential nanosunscreens, there’s also my July 22, 2010 posting.

Sunscreen and nanoparticles from ivy

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I like a story about science research that starts with a question even if it does lead to another nanosunscreen posting this year (from a news item on Science Daily),

“What makes the ivy in [the] backyard cling to the fence so tightly?”

Associate professor of bioengineering at the University of Tennessee, Knoxville, Mingjun Zhang, asked himself that question one day while watching his son play in their back yard. Zhang’s answer may lead to the development of a new type of nanosunscreen, one that uses plant-based nanoparticles rather than metal-based ones.

Zhang speculated the greenery’s hidden power lay within a yellowish material secreted by the ivy for surface climbing. He placed this material onto a silicon wafer and examined it under an atomic force microscope and was surprised by what they found — lots of nanoparticles, tiny particles 1,000 times thinner than the diameter of a human hair. The properties of these tiny bits create the ability for the vine leaves to hold almost 2 million more times than its weight. It also has the ability to soak up and disperse light which is integral to sunscreens. [emphasis mine]

Michael Berger at Nanowerk has written an article (Harmless natural nanoparticles show potential to replace metal-based nanoparticles in sunscreen) discussing Dr. Zhang’s work in more depth,

Quite impressively, the team’s study indicates that ivy nanoparticles can improve the extinction of ultraviolet light at least four times better than its metal counterparts.

Zhang points out that sunscreens made with ivy nanoparticles may not need to be reapplied after swimming. “That’s because the plant’s nanoparticles are a bit more adhesive so sunscreens made with them may not wash off as easily as traditional sunscreens,” he says. “And while sunscreens made with metal-based nanoparticles give the skin a white tinge, sunscreens made with ivy nanoparticles are virtually invisible when applied to the skin.”

This certainly looks promising but they don’t seem to be anywhere near to producing sunscreens containing ivy nanoparticles.