1. Biomaterials
2. Mobility & Infrastructure
3. Computing and Electronics
4. Energy (lower priority)
5. Security (lower priority)
All projects should include a view to sustainability in regard to raw materials, carbon or energy efficiency, waste and recyclability.
Up to three IMat Graduate Student Fellows (IGSF) will be selected in this seed funding program. If selected, a $3.5K direct funding grant will “top-off” existing annual GRA stipends with the intent of adding value to the existing thesis-directed materials research workflows by introducing one or more of the following elements:
Requirements:
· Graduate students in any academic unit may apply.
· The IGSF should seek to incorporate this experience into the student’s final thesis product.
· Awards should be used for augmentation of stipends of existing thesis-directed GRAs and not for bridging between other means of support or for augmenting TA compensation.
· Students should engage in training sessions and workshops for materials data science, and to serve as ambassadors/mentors for other students in their group and beyond.
· A statement from their research advisor regarding interest in, and commitment to these requirements is necessary as part of the proposal
· Students are encouraged to consider enrolling in the following materials informatics courses:
Deliverables:
-Evidence of incorporation of these areas into the workstream of the student’s thesis research.
-Students should complete the two MOOC course sequence on Coursera:
-Report due June 30, 2020 detailing: aspects explored, new capabilities developed, and how this experience has impacted their research group and/or academic unit, and benefit to GT research capabilities and/or user facilities, broadly speaking.
IGSF application format:
Review Criteria:
Applications will be reviewed by a committee composed of Georgia Tech faculty. Final award selections will balance available funds with requests and review recommendations. Funding to be allocated depends upon the submission of proposals that are considered responsive to the call as outlined and recommended for support in the review process.
Applications should be submitted to https://gatech.infoready4.com/ by 11:59P ET on Friday, February 21, 2020. Award selections will be made in March 2020 and funds will be disbursed in equal increments on April, May and June 2020 pay dates.
Questions:
Dr. Jud Ready, IMat Deputy Director - Innovation Initiatives jud.ready@gatech.edu
404-407-6036
]]>Since October 2019, more than 5,700 students, faculty, staff, alumni, campus partners, and community leaders provided input via surveys, in-person meetings, workshops, informal sessions, and webinars. They shared varied perspectives, aspirations, and dreams to help shape the future of the Institute.
The steering committee worked in tandem with the visioning and collection process to analyze volumes of raw data and provide the building blocks for the Institute’s new mission, vision, and values, and strategic impact theme areas.
Members of the Georgia Tech community are encouraged to visit strategicplan.gatech.edu to review the draft of the foundational narrative, vision, theme and values and beliefs that will ultimately shape the strategic plan. There, you can submit feedback through March 20, and learn more about the process, the data collection and analysis methodology, and next steps.
Applying to a Working Group
Starting now in Phase two — goal setting— working groups will cluster around six strategic themes. Applications are currently being accepted for any who are interested in serving on one of six themed working groups.
The strategic themes are as follows:
The working groups will meet between March and May, and work to identify goals, objectives and measures of success necessary to bring those themes to life. The groups are expected to meet on a regular basis, with time commitments expected to be between four to six hours each week.
Interested working group applicants must complete the Institute Strategic Planning Working Group Application Form by Wednesday Feb. 26, 2020.
Questions can be sent to strategicplan@gatech.edu.
]]>The technique, called surface-activated bonding, uses an ion source in a high-vacuum environment to first clean the surfaces of the GaN and diamond, which activates the surfaces by creating dangling bonds. Introducing small amounts of silicon into the ion beams facilitates forming strong atomic bonds at room temperature, allowing the direct bonding of the GaN and single-crystal diamond to fabricate high-electron-mobility transistors (HEMTs).
The resulting interface layer from GaN to single-crystal diamond is just four nanometers thick, allowing heat dissipation up to two times more efficient than in the state-of-the-art GaN-on-diamond HEMTs by eliminating the low-quality diamond left over from nanocrystalline diamond growth. Diamond is currently integrated with GaN using crystalline growth techniques that produce a thicker interface layer and low-quality nanocrystalline diamond near the interface. Additionally, the new process can be done at room temperature using surface-activated bonding techniques, reducing the thermal stress applied to the devices.
“This technique allows us to place high thermal conductivity materials much closer to the active device regions in gallium nitride,” said Samuel Graham, the Eugene C. Gwaltney Jr. School Chair and professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering. “The performance allows us to maximize the performance for gallium nitride on diamond systems. This will allow engineers to custom design future semiconductors for better multifunctional operation.”
The research, conducted in collaboration with scientists from Meisei University and Waseda University in Japan, was reported February 19 in the journal ACS Applied Materials and Interfaces. The work was supported by a multidisciplinary university research initiative (MURI) project from the U.S. Office of Naval Research (ONR).
For high-power electronic applications using materials such as GaN in miniaturized devices, heat dissipation can be a limiting factor in power densities imposed on the devices. By adding a layer of diamond, which conducts heat five times better than copper, engineers have tried to spread and dissipate the thermal energy.
However, when diamond films are grown on GaN, they must be seeded with nanocrystalline particles around 30 nanometers in diameter, and this layer of nanocrystalline diamond has low thermal conductivity – which adds resistance to the flow of heat into the bulk diamond film. In addition, the growth takes place at high temperatures, which can create stress-producing cracks in the resulting transistors.
“In the currently used growth technique, you don’t really reach the high thermal conductivity properties of the microcrystalline diamond layer until you are a few microns away from the interface,” Graham said. “The materials near the interface just don’t have good thermal properties. This bonding technique allows us to start with ultra-high thermal conductivity diamond right at the interface.”
By creating a thinner interface, the surface-activated bonding technique moves the thermal dissipation closer to the GaN heat source.
“Our bonding technique brings high thermal conductivity single crystal diamond closer to the hotspots in the GaN devices, which has the potential to reshape the way these devices are cooled,” said Zhe Cheng, a recent Georgia Tech Ph.D. graduate who is the paper’s first author. “And because the bonding takes place near room temperature, we can avoid thermal stresses that can damage the devices.”
That reduction in thermal stress can be significant, going from as much as 900 megapascals (MPa) to less than 100 MPa with the room temperature technique. “This low stress bonding allows for thick layers of diamond to be integrated with the GaN and provides a method for diamond integration with other semiconductor materials,” Graham said.
Beyond the GaN and diamond, the technique can be used with other semiconductors, such as gallium oxide, and other thermal conductors, such as silicon carbide. Graham said the technique has broad applications to bond electronic materials where thin interfacial layers are advantageous.
“This new pathway gives us the ability to mix and match materials,” he said. “This can provide us with great electrical properties, but the clear advantage is a vastly superior thermal interface. We believe this will prove to be the best technology available so far for integrating wide bandgap materials with thermally conducting substrates.”
In future work, the researchers plan to study other ion sources and evaluate other materials that could be integrated using the technique.
“We have the ability to choose processing conditions as well as the substrate and semiconductor material to engineer heterogenous substrates for wide bandgap devices,” Graham said. “That allows us to choose the materials and integrate them to maximize electrical, thermal, and mechanical properties.”
In addition to the researchers already mentioned, the paper included co-corresponding author Fengwen Mu from Meisei University and Waseda University in Japan, Luke Yates from Georgia Tech, and Tadatomo Suga from Meisei University.
This research was supported by the U.S. Office of Naval Research (ONR) through MURI Grant No. N00014-18-1-2429. Any findings, conclusions, and recommendations are those of the authors and not necessarily of the Office of Naval Research.
CITATION: Zhe Cheng, Fengwen Mu, Luke Yates, Tadatomo Suga and Samuel Graham, “Interfacial Thermal Conductance across Room-Temperature-Bonded GaN/Diamond Interfaces for GaN-on-Diamond Devices” (ACS Appl. Mater. Interfaces, 2020, 12, 8376?8384). https://doi.org/10.1021/acsami.9b16959
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]]>In this case, however, the race is to improvise ventilators, face shields, respirators, surgical gowns, disinfectant wipes, and other healthcare gear to help the hundreds of thousands of people expected to swamp hospitals with waves of critical COVID-19 illness over the next several weeks. The demand for ventilators alone could be four times more than already overwhelmed hospitals can provide.
Using 3D-printed parts, plastic-lined tablecloths intended for birthday parties, laser-cut gears, and similar substitutions, a research team from universities on two continents is racing to develop “do-it-yourself” healthcare gear that can be assembled where it’s needed from components available locally. Team members figure they have about two weeks to get the designs right and share them with anyone who can help with the needs.
“We’re trying to figure out how to get these things to scale in the time we have,” said Shannon Yee, an associate professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering who’s working on the ventilator issue with a half-dozen colleagues at Georgia Tech and other universities. “We are looking at producing things very quickly and this is where having contacts with mature manufacturing sources is going to help.”
Supplying Face Shields to the Medical Community
The Wallace H. Coulter Department of Biomedical Engineering at Emory and Georgia Tech serves as a bridge between healthcare needs and the broad technical know-how at Georgia Tech, and Georgia Tech researchers are talking regularly with hospital systems to discuss their needs. So far, hand sanitizer, disinfectant wipes, face shields, respirator masks, and ventilators have been identified as critical needs. Using resources of the Flowers Invention Studio – such as 3D printing – the group has already produced 1,000 face shields and is preparing to fabricate thousands more in the form of kits that hospitals can assemble.
"With the significant challenges on our supply chain, we need strategies to provide personal protective equipment (PPE) for healthcare staff," said Dr. Charles Brown, CEO of Physician Enterprise at Piedmont Healthcare. "We have mechanisms in place to develop ideas and are working with Georgia Tech and the Global Center for Medical Innovation (GCMI) to advance them to what we can use."
Georgia Tech faculty members, students and GCMI worked on multiple face shield designs, talking with clinicians at Children’s Healthcare of Atlanta, Emory Healthcare and Piedmont to evaluate and iterate. The result was two different designs intended for specific uses in hospital facilities, where face shields protect clinicians from splashes and help extend the life of soft respirators intended to filter out virus particles.
“The team has worked hard to identify materials suppliers and define simple and scalable solutions to meet this challenge,” said Sam Graham, chair of the Woodruff School of Mechanical Engineering. “We are fortunate to have partners ready to team up with us to help address some of the shortfalls in medical equipment that hospitals are experiencing."
To scale up fabrication beyond the Georgia Tech campus, the team focused on simple designs that could be shared with and produced by individuals with access to a makerspace – and major manufacturers with injection molding capabilities. The team plans to make the designs available for anyone with laser cutting or 3D printing capabilities.
“Initially we were just thinking about meeting the needs of Atlanta, but cities everywhere need them,” said Saad Bhamla, an assistant professor in the School of Chemical and Biomolecular Engineering who specializes in “frugal science” – creating inexpensive lab devices. “We have created great models that can be used to create a pipeline of instructions that others can use. The face shields will set the stage for other device models as they become available.”
The group is leveraging Georgia Tech contacts with companies to identify suppliers for alternative materials that can go into their “Apollo 13” devices. Team members, including Christopher Saldana, an associate professor in the Woodruff School, are working with GCMI on those issues, using equipment in Georgia Tech’s maker spaces and elsewhere.
"The Georgia Tech mechanical engineering team is working to modify open source face shield designs so they can be manufactured in high volumes for the rapid response environment that COVID-19 requires,” said Christopher Saldana, an associate professor in the Woodruff School. “Our team has modified these designs using a range of product and process optimization methods, including removing certain features and standardizing tool use. By working on cross-functional and cross-disciplinary teams and directly involving healthcare practitioners and high-volume manufacturers, we will be able to respond to this effort at the scale and speed required."
Bringing Georgia Tech’s expertise together to address the challenges – and develop collaborations – has been done behind the scenes by people like Sherry Farrugia, chief operating and strategy officer for the Children’s Healthcare of Atlanta Pediatric Technology Center.
“Serving as kind of a chief strategy officer, my work is to help bridge the gaps, focus the teams, rally the troops, and make critical connections,” she said. “Doing this requires a deep knowledge of who’s doing what on campus, as well as a strong network in the private sector.”
The Supply Chain Challenge
The team is launching a website (www.research.gatech.edu/rapid-response) to both quantify the needs for face shields and solicit supplies of materials. Because the world’s supply chains are unable to ship conventional PPE components, they are looking for alternatives that may not now be part of that production.
The challenge is that everyone is scrambling to find equipment and materials in an international supply chain that has already been depleted by months-long demands from countries that dealt with the virus earlier: China, Italy and South Korea. As the healthcare demands ramp up in the United States, hospitals will have to be more creative in meeting the needs that their traditional sources may not be able to supply.
"Countries on the trailing end of the pandemic are facing supply chain issues that countries with earlier pandemics didn't have to face," said Michael O'Toole, Executive Director of Quality Improvement at Piedmont and a Georgia Tech engineering graduate. "We've got to get these supplies, and its a critical need already. If we can't get them from commercial or government sources, we're going to have to make them ourselves."
With significant efforts going into design of locally sourced equipment, expertise on medical device prototyping and approval is needed. That is coming from a network of alumni and local companies and GCMI, a Georgia Tech-affiliated organization that works with device manufacturers around the world to translate designs into devices that can be manufactured quickly and cost effectively.
“The goal right now is to develop solutions that can be sourced locally and that we can produce now,” said Tiffany Wilson, GCMI’s CEO. “We are working with Georgia Tech and others on how we can suggest modifying the designs to optimize them for the current environment. We are helping make sure designs are clinically validated with an eye toward scalability.”
Beyond its experience with medical devices, GCMI is also helping source materials and components, and working with regulators at the FDA to help reduce risks in the responses.
“There have been changes in some of the standards and new guidance from the FDA to enable faster production to open up the supply chain to get more masks and respirators into the market,” Wilson said. “There are still levels of control and risk mitigations strategies that we need to focus on. We’re staying on top of those changes.”
Research on Possible Solutions for Other Shortages
While the face shield is the most mature project the team is developing, researchers are also looking at other needs of the medical community. Among them are ventilators, disinfecting wipes, and respirators.
An example of an Apollo 13 project may be ventilators that are used to help critically ill patients breathe. Traditional equipment makers are working as fast as they can, but that may not be fast enough. To achieve a globally scalable makeshift ventilator will require minimizing the number of parts and thinking about mechanical simplicity, Yee said.
Leon Williams, head of the Centre for Competitive Creative Design at Cranfield University, is working with Georgia Tech researchers to create a makeshift ventilator based on the bag-valve-mask (BVM) – also known as an Ambu bag – a hand-held mechanical resuscitation device already available at hospitals.
Through a system of laser-cut gears and other components, the preliminary concept would use a simple three-volt motor to compress the bag and push air into the lungs of a critically ill patient. Among the challenges is extending the lifetime of the bags, which are not designed for long-term use.
“We need to understand everything about the ventilators that are already in use,” said Susan Margulies, chair of the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University. “By understanding how everything works, we can modify the design to use the components we can get.”
As with face shields, the group expects to make its plans widely available for other groups to iterate and produce. “There is a lot of activity here that is going to move this forward,” said Devesh Ranjan, associate chair for research in the Woodruff School of Mechanical Engineering, who is coordinating several of the Georgia Tech Rapid-Response projects on campus.
Another identified need is for disinfecting wipes, which seem like a simple enough product: a nonwoven material and a solution based on either alcohol or bleach. The material and solutions seem to be available; the problem is locating the industrial-sized containers to hold them.
“We’ve been looking for containers for the wipes commercially,” said Graham. “What we are finding is that the issue is the containers, but we are looking at other solutions.” He’s working with David Sholl, chair of the School of Chemical and Biomolecular Engineering, to identify potential suppliers.
Respirators, Swabs and Gowns
Protecting healthcare workers from the coronavirus requires a special type of respirator, soft face masks that remove virus particles from the air. Because the virus particles are so small, hundreds of nanometers in diameter, that protection requires high-efficiency filtration materials that until recently were mostly manufactured in China.
“The filters are not being produced at the rates that are needed, so we have been thinking about what we can put together that approximates an N95 filter that’s needed to protect healthcare workers,” said Ryan Lively, an associate professor in the School of Chemical and Biomolecular Engineering. “We need to make something that can be produced out of homemade goods, then verify that it can do the filtering needed.”
Lively has been experimenting with alternatives, such as high-efficiency filtration materials manufactured for HVAC systems that could be sewn inside a fabric pouch. “There are journal papers out there showing filtration materials that are not as good as N95 are still effective at increasing rejection of the virus particles,” he said.
If these work as needed, Lively could produce limited numbers in his lab. “We have estimated that we can produce 700 masks per week using the pilot line that we have for research and repurposing it for cranking out hydrophobic fiber media,” he said. “That won’t solve the problem, but it will help meet a very critical need.”
The swabs used for COVID-19 testing are also in short supply, as are gowns designed to protect healthcare workers. Carson Meredith, director of the Renewable Bioproducts Institute, is tracking down alternative sources from among the many manufacturers who are members of the Georgia Tech interdisciplinary research institute.
“The idea is to take a basic material intended for a different function and transform it into the products that we need,” he said. One example is a material manufactured for party tablecloths - plastic on one side to prevent spills from going through, and paper on the other for festive designs. “We’re looking at whether the machinery that produces those can be rapidly turned into making a temporary gown.”
The research team meets by phone daily to update each other on what’s been done and to share ideas. They follow international Slack channels to know what other similar groups are doing across the U.S. and the world.
They know their prototype production equipment can’t meet the world’s needs, so they’re sharing plans with others who may have capabilities. Ultimately, major manufacturers will catch up, but that could take months – perhaps too long for the expected COVID-19 infection curve.
“The best thing we can do is share that information broadly to try to come up with solutions that use parts that can be sourced locally,” Yee said, referring to the ventilator project. “Simple solutions using motors that people can get anywhere, structures that can be 3D-printed and materials that can be hand-cut with saws may get us through this.”
Article updated March 26, 2020
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]]>“Our expectation is that frontline healthcare workers interacting with COVID-19 patients will use certified PPE,” said Ryan Lively, an associate professor in Georgia Tech’s School of Chemical and Biomolecular Engineering. “But for situations that don’t involve intimate and prolonged interactions with COVID-19 infected individuals, we believe that DIY cloth face masks combined with proper social distancing etiquette will help slow the spread of this virus.”
While the underlying physics of filtration are complicated, Lively and colleagues believe that two or more layers of a tightly woven, knitted, or nonwoven fabric can provide at least a partial barrier to virus-containing droplets, which combined with social distancing, can reduce the likelihood of virus transmission.
“Equally, important though, is the way that users fit, wear, handle, and remove the face mask,” said Mark Losego, an assistant professor in Georgia Tech’s School of Materials Science and Engineering. “Because the mask will be touching your face, it and your hands should be clean before putting it on. The mask should be snug but not uncomfortable.”
Gaps around the nose and chin should be minimized. Once wearing the mask, you should avoid touching or moving the mask; don’t pull the mask down to cough or sneeze! The mask is expected to capture germs, so it should be removed by touching only the straps; otherwise, you will contaminate your hands.
Equally important to blocking virus-containing droplets is that the mask materials be breathable and non-hazardous for inhalation. “For example, there is some danger of glass fibers within HEPA or MERV filters being inhaled if appropriate blocking layers are not included,” said Lively. “Most apparel or home goods textiles are safe. However, if you smell a chemical odor from the material, you should probably avoid using it for a mask.”
Upon returning home from an errand, the mask should be discarded or thrown in the clothes washer and cleaned before being used again. If the fabric mask does get wet from another individual’s cough or sneeze, the mask should be removed quickly at a safe distance. The team recommends reviewing both the World Health Organization (WHO) link and Centers for Disease Control and Prevention (CDC) guidelines for mask wearing.
A new website (www.research.gatech.edu/rapid-response) has been created to bring together recommendations and templates for making face masks. The website provides guidance for making unsewn, sewn, glued, or 3D-printed face masks.
The recommendations resulted from consulting with a team of experts in materials, chemical and mechanical engineering, filtration processes, and production design. “We have also interacted with relevant stakeholders, including hospitals and manufacturers, and studied the peer-reviewed literature to make recommendations based on scientific evidence,” said Lively.
On the website, the researchers suggest alternatives for materials that are in short supply. For instance, high-performance HEPA furnace filters can be used with 3D printed masks to create a respirator, provided the HEPA filters are installed in between two blocking layers of nonwoven fabric. Reusable polypropylene grocery bags without a shiny film can be used as the droplet-repelling outer shell of the masks.
The new website includes directions, recommendations, files for 3D printers and more. The team is actively testing fabric materials to provide more specific recommendations for which fabrics to use and which to avoid. A rudimentary DIY test using a water spray bottle is described to make an initial assessment of how suitable a fabric is for a mask.
Masks produced or tested with directions from the site do not meet the standards of federal agencies such as NIOSH, OSHA or the FDA.
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]]>Researchers at the Georgia Institute of Technology have developed, in a new study, a method of making gecko-inspired adhesive materials that is much more cost-effective than current methods. It could enable mass production and the spread of the versatile gripping strips to manufacturing and homes.
Polymers with “gecko adhesion” surfaces could be used to make extremely versatile grippers to pick up very different objects even on the same assembly line. They could make picture hanging easy by adhering to both the picture and the wall at the same time. Vacuum cleaner robots with gecko adhesion could someday scoot up tall buildings to clean facades.
“With the exception of things like Teflon, it will adhere to anything. This is a clear advantage in manufacturing because we don’t have to prepare the gripper for specific surfaces we want to lift. Gecko-inspired adhesives can lift flat objects like boxes then turn around and lift curved objects like eggs and vegetables,” said Michael Varenberg, the study’s principal investigator and an assistant professor in Georgia Tech’s George W. Woodruff School of Mechanical Engineering.
Current grippers on assembly lines, such as clamps, magnets, and suction cups, can each lift limited ranges of objects. Grippers based on gecko-inspired surfaces, which are dry and contain no glue or goo, could replace many grippers or just fill in capability gaps left by other gripping mechanisms.
The adhesion comes from protrusions a few hundred microns in size that often look like sections of short, floppy walls running parallel to each other across the material’s surface. How they work by mimicking geckos’ feet is explained below.
Up to now, molding has produced these mesoscale walls by pouring ingredients onto a template, letting the mixture react and set to a flexible polymer then removing it from the mold. But the method is inconvenient.
“Molding techniques are expensive and time-consuming processes. And there are issues with getting the gecko-like material to release from the template, which can disturb the quality of the attachment surface,” Varenberg said.
The researchers’ new method formed those walls by pouring ingredients onto a smooth surface instead of a mold, letting the polymer partially set then dipping rows of laboratory razor blades into it. The material set a little more around the blades, which were then drawn out, leaving behind micron-scale indentations surrounded by the desired walls.
Varenberg and first author Jae-Kang Kim published details of their new method in the journal ACS Applied Materials & Interfaces on April 6, 2020.
Though the new method is easier than molding, developing it took a year of dipping, drawing, and readjusting while surveying finicky details under an electron microscope.
“There are many parameters to control: Viscosity and temperature of the liquid; timing, speed, and distance of withdrawing the blades. We needed enough plasticity of the setting polymer to the blades to stretch the walls up, and not so much rigidity that would lead the walls to rip up,” Varenberg said.
Gecko-inspired surfaces have a fine topography on a micron-scale and sometimes even on a nanoscale, and surfaces made via molding are usually the most precise. But such perfection is unnecessary; the materials made with the new method did the job well and were also markedly robust.
“Many researchers demonstrating gecko adhesion have to do it in a cleanroom in clean gear. Our system just plain works in normal settings. It is robust and simple, and I think it has good potential for use in industry and homes,” said Varenberg, who studies surfaces in nature to mimic their advantageous qualities in human-made materials.
[Ready for graduate school with social distancing? Here's how to apply to Georgia Tech.]
Behold the gecko’s foot. It has ridges on its toes, and this has led some in the past to think their feet stick by suction or some kind of clutching by the skin.
But electron microscopes reveal a deeper structure – spatula-shaped bristly fibrils protrude a few dozen microns long off those ridges. The fibrils make such thorough contact with surfaces down to the nanoscale that weak attractions between atoms on both sides appear to add up enormously to create overall strong adhesion.
In place of fluff, engineers have developed rows of shapes covering materials that produce the effect. A common shape makes a material’s surface look like a field of mushrooms that are a few hundred microns in size; another is rows of short walls like those in this study.
“The mushroom patterns touch a surface, and they are attached straightaway, but detaching requires applying forces that can be disadvantageous. The wall-shaped projections require minor shear force like a tug or a gentle grab to generate adherence, but that is easy, and letting go of the object is uncomplicated, too,” Varenberg said.
Varenberg’s research team used the drawing method to make walls with U-shaped spaces in between them and walls with V-shaped spaces in between. They worked with polyvinylsiloxane (PVS) and polyurethane (PU). The V-shape made in PVS worked best, but polyurethane is the better material for industry, so Vanenberg’s group will now work toward achieving the V-shape gecko gripping pattern in PU for the best possible combination.
Also read: Lung-heart super sensor on a chip tinier than a ladybug
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]]>Flow of lithium ions into and out of alloy battery anodes has long been a limiting factor in how much energy batteries could hold using conventional materials. Too much ion flow causes anode materials to swell and then shrink during charge-discharge cycles, causing mechanical degradation that shortens battery life. To address that issue, researchers have previously developed hollow “yolk-shell” nanoparticles that accommodate the volume change caused by ion flow, but fabricating them has been complex and costly.
Now, a research team has discovered that particles a thousand times smaller than the width of a human hair spontaneously form hollow structures during the charge-discharge cycle without changing size, allowing more ion flow without damaging the anodes. The research was reported June 1 in the journal Nature Nanotechnology.
“Intentionally engineering hollow nanomaterials has been done for a while now, and it is a promising approach for improving the lifetime and stability of batteries with high energy density,” said Matthew McDowell, assistant professor in the George W. Woodruff School of Mechanical Engineering and the School of Materials Science and Engineering at the Georgia Institute of Technology. “The problem has been that directly synthesizing these hollow nanostructures at the large scales needed for commercial applications is challenging and expensive. Our discovery could offer an easier, streamlined process that could lead to improved performance in a way that is similar to the intentionally engineered hollow structures.”
The researchers made their discovery using a high-resolution electron microscope that allowed them to directly visualize battery reactions as they occur at the nanoscale. “This is a tricky type of experiment, but if you are patient and do the experiments right, you can learn really important things about how the materials behave in batteries,” McDowell said.
The team, which included researchers from ETH Zürich and Oak Ridge National Laboratory, also used modeling to create a theoretical framework for understanding why the nanoparticles spontaneously hollow — instead of shrinking — during removal of lithium from the battery.
The ability to form and reversibly fill hollow particles during battery cycling occurs only in oxide-coated antimony nanocrystals that are less than approximately 30 nanometers in diameter. The research team found that the behavior arises from a resilient native oxide layer that allows for initial expansion during lithiation — flow of ions into the anode — but mechanically prevents shrinkage as antimony forms voids during the removal of ions, a process known as delithiation.
The finding was a bit of a surprise because earlier work on related materials had been performed on larger particles, which expand and shrink instead of forming hollow structures. “When we first observed the distinctive hollowing behavior, it was very exciting and we immediately knew this could have important implications for battery performance,” McDowell said.
Antimony is relatively expensive and not currently used in commercial battery electrodes. But McDowell believes the spontaneous hollowing may also occur in less costly related materials such as tin. Next steps would include testing other materials and mapping a pathway to commercial scale-up.
“It would be interesting to test other materials to see if they transform according to a similar hollowing mechanism,” he said. “This could expand the range of materials available for use in batteries. The small test batteries we fabricated showed promising charge-discharge performance, so we would like to evaluate the materials in larger batteries.”
Though they may be costly, the self-hollowing antimony nanocrystals have another interesting property: they could also be used in sodium-ion and potassium-ion batteries, emerging systems for which much more research must be done.
“This work advances our understanding of how this type of material evolves inside batteries,” McDowell said. “This information will be critical for implementing the material or related materials in the next generation of lithium-ion batteries, which will be able to store more energy and be just as durable as the batteries we have today.”
In addition to McDowell, the paper’s authors include Matthew Boebinger from Georgia Tech; Olesya Yarema, Maksym Yarema, and Vanessa Wood from the Department of Information Technology and Electrical Engineering at ETH Zürich , and Kinga Unocic and Raymond Unocic from the Center for Nanophase Materials Science at Oak Ridge National Laboratory.
This work was performed at the Georgia Tech Materials Characterization Facility and the Institute for Electronics and Nanotechnology, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (Grant ECCS-1542174). Support also came from the Department of Energy Office of Science Graduate Student Research Program for research performed at Oak Ridge National Laboratory. A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. Support was also provided by a Sloan Research Fellowship in Chemistry from the Alfred P. Sloan Foundation and by the Swiss National Science foundation via an Ambizione Fellowship (no. 161249). The content is solely the responsibility of the authors and does not necessarily represent the official views of the sponsoring organizations.
CITATION: Matthew G. Boebinger, et al., “Spontaneous and reversible hollowing of alloy anode nanocrystals for stable battery cycling” (Nature Nanotechnology, 2020). https://doi.org/10.1038/s41565-020-0690-9
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]]>The professor at the Georgia Institute of Technology rallied colleagues and partners around the cause in March, and by early June, they had replaced a key component of hand sanitizer, created a new supply chain, and initiated their own donation of 7,000 gallons of a newly designed sanitizer to medical facilities.
Its name: Han-I-Size White & Gold, named for the colors of Georgia Tech. The new supply chain also may ensure that hand sanitizer producers across the country do not run out of the main active ingredient, alcohol, but the team’s path to success was a stony labyrinth.
“This project was on life support so many times because people did not understand how severe this shortage was going to be,” said Marder, a Regents Professor in Georgia Tech’s School of Chemistry and Biochemistry. “I called hospitals and institutions to assess the need and heard the same thing over and over: ‘No, we just got a delivery. We have no need. You’re wasting your time.’”
Marder was not. Contacts at major chemical suppliers of hand sanitizer ingredients said that a critical shortage of alcohol, particularly the one usually in hand sanitizer, isopropanol, was coming.
“Isopropanol plants in the U.S. were running at full capacity and still didn’t have enough. People were using pharmaceutical-grade ethanol now, too, but it was also in short supply. We weren’t going to have enough of either; I mean the whole United States was running low,” Marder said.
Marder hastily drafted Chris Luettgen, a professor of practice in Georgia Tech’s School of Chemical and Biomolecular Engineering, George White, interim vice president of Georgia Tech’s Office of Industry Collaboration, and Atif Dabdoub, a Georgia Tech alumnus and owner of a local chemical company, Unichem Technologies, Inc.
To the three chemists and the business professional, it seemed simple: Mix alcohol with water, peroxide, and the moisturizer glycerin then bottle and ship it. That bubble burst quickly.
Luettgen, who had worked in the consumer products industry for 25 years at Kimberly-Clark Corporation and knew how to take products to market, had to plow through constant unexpected supply chain barriers and bureaucracy while White forged connections between companies. Neither the supply chain nor the business relationships had existed before, and the teams’ phones stayed glued to their ears night and day as they created them from scratch.
“When I worked for Kimberly-Clark, getting a new product out would take the company nine to 18 months, and the three of us had to get this done in weeks. The demand was there, and people were getting sick in some cases from lack of sanitizing. We felt speed was necessary to meet the growing demand. Seth told me to push this across the goal line, and I put everything into it,” Luettgen said.
“Georgia Tech is about the power to convene. Companies and stakeholders are eager to come to the table here to make things happen,” White said about forging new business ties. “Not everyone has that incredible recognition as a problem solver with the brainpower amassed here.”
Purchasing truckloads of alcohol was priority one.
Boutique liquor distilleries in Georgia were already converting to sanitizer ethyl alcohol production, but output was nowhere near enough to meet demand. ExxonMobil connected the team with Eco-Energy, a company that handles fuel-grade ethanol as a gasoline additive.
“The amount of ethanol that’s made for fuel in the U.S. is 1,500 times the amount of the isopropanol made. They could drain off about 1 percent of what is used for fuel and double or triple the amount of alcohol available for hand sanitizer in this country. And the fuel companies wouldn’t even notice it was gone, especially since hardly anyone was driving anymore,” Marder said.
But then prospective hand sanitizer distributors crimped their noses at that ethanol, saying it smelled odd.
“I thought, ‘This has the makings of a screenplay.’ I asked the distributor if we could come over to smell a sample for ourselves,” White said. “It needed a little love.”
Eco-Fuels produced the highly refined ethanol and then processed it through carbon filtration to increase purity and reduce odor. Atlanta-based chemical manufacturer, Momar, Inc., oversaw production, packaging, and distribution of Han-I-Size White & Gold.
The Georgia Tech team garnered funding through a donation from insurer Aflac Incorporated allocated through the Global Center for Medical Innovation (GCMI), a Georgia Tech affiliated non-profit organization that guides new experimental medical solutions to market. Aflac’s gift of $2 million through GCMI has also expedited the development, production, and purchase of other PPE to donate to health care workers.
In addition, GCMI helped guide the hand sanitizer through regulatory processes and to market. In a another development, the U.S. Food and Drug Administration was also aware of the dire shortage of alcohol for sanitizer and issued waivers for the pandemic to allow for use of ethanol in sanitizers without having to meet usual specifications.
Arkema, Inc. donated hydrogen peroxide, which was delivered to PSG Functional Materials, which mixed and packaged the product then shipped with no delivery fee to Atlanta. Though water is ubiquitous, hand sanitizer requires purified water, and the Coca-Cola Company donated a tanker truck of it just when White was pondering desperate measures.
“If I have to get a truck to go pick up water and drive it, I’ll do it myself,” he said.
Finally, the first few hundred gallons of donated Han-I-Size White & Gold rolled into Piedmont Healthcare in Atlanta and Brightmoor Nursing Center in Griffin, Georgia, in the second week of June 2020.
GCMI is facilitating donations of the 7,000 gallons nationwide. Separate from the Aflac-financed donations, Momar will continue to manufacture the new hand sanitizing formula commercially to include in its regular product lineup, and Georgia Tech will be able to purchase it at a reduced rate to help protect researchers now returning to their labs.
The new supply chain, the first of its kind, of “waiver-grade” ethanol has given hand sanitizer producers across the country a new opportunity to re-supply America.
“Hopefully, we helped solved a national need,” Luettgen said.
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Writer & media inquiries: Ben Brumfield, ben.brumfield@comm.gatech.edu or John Toon (404-894-6986), jtoon@gatech.edu.
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]]>Conducted by researchers at the Georgia Institute of Technology using two pathogens similar to the novel coronavirus, the study found that ozone can inactivate viruses on items such as Tyvek gowns, polycarbonate face shields, goggles, and respirator masks without damaging them — as long as they don’t include stapled-on elastic straps. The study found that the consistency and effectiveness of the ozone treatment depended on maintaining relative humidity of at least 50% in chambers used for disinfection.
“Ozone is one of the friendliest and cleanest ways of deactivating viruses and killing most any pathogen,” said M.G. Finn, chair of Georgia Tech’s School of Chemistry and Biochemistry, who led the study. “It does not leave a residue; it’s easy to generate from atmospheric air, and it’s easy to use from an equipment perspective.”
Findings of the research are described in a paper posted to the medRxiv preprint server and will be submitted to a journal for peer review and publication. Ozone can be produced with inexpensive equipment by exposing oxygen in the atmosphere to ultraviolet light, or through an electrical discharge such as a spark.
During local and regional peaks in coronavirus infection, shortages of personal protective equipment (PPE) can force hospitals and other healthcare facilities to reuse PPE that was intended for a single use. Facilities have used ultraviolet light, vaporized hydrogen peroxide, heat, alcohol and other techniques to disinfect these items, but until recently, there had not been much interest in ozone disinfection, Finn said.
Ozone is widely used for disinfecting wastewater, purifying drinking water, sanitizing food items, and disinfecting certain types of equipment — even clothing. Ozone disinfection cabinets are commercially available, taking advantage of the oxidizing effects of the gas to kill bacteria and inactivate viruses.
“There was no reason to think it wouldn’t work, but we could find no examples of testing done on a variety of personal protective equipment,” Finn said. “We wanted to contribute to meeting the needs of hospitals and other healthcare organizations to show that this technique could work against pathogens similar to the coronavirus.”
Phil Santangelo, a virologist in the Wallace H. Coulter Department of Biomedical Engineering, recommended two respiratory viruses — influenza A and respiratory syncytial virus (RSV) – as surrogates for coronavirus. The two are known as “enveloped” viruses because, like coronavirus, they are surrounded by a lipid outer membrane. Influenza and RSV are less dangerous than the SARS-CoV-2 coronavirus, allowing the Georgia Tech researchers to study them without high-containment laboratory facilities.
Santangelo, Finn, and their team devised a test procedure in which solutions containing the two viruses were placed onto samples of the PPE materials under study. The solutions were allowed to dry before the samples were placed in a chamber into which ozone was introduced at varying concentrations as low as 20 parts per million. After treatment for different lengths of time, the researchers tested the PPE samples to determine whether or not any of the viruses on the treated surfaces could infect cells grown in the laboratory. The entire test procedure required about a day and a half.
“The protocol we set up reports very sensitively on whether or not the virus could reproduce, and we found that the ozone was very successful in rendering them harmless,” Finn said. “Oxidizing biological samples to a significant extent is enough to inactivate a virus. Either the genetic material or the outer shell of the virus would be damaged enough that it could no longer infect a host cell.”
Loren Williams, a professor in School of Chemistry and Biochemistry, introduced the research team to a manufacturer of ozone disinfection chambers, which allowed evaluation of the equipment using the test protocol. During the test, the researchers learned that having sufficient relative humidity in the chamber — at least 50% — was essential for rapidly inactivating the viruses in a consistent manner.
After subjecting face masks and respirators to ozone disinfection, the team worked with Associate Professor Nga Lee (Sally) Ng from the School of Chemical and Biomolecular Engineering and the School of Earth and Atmospheric Sciences to evaluate the filtration capabilities of the items. The ozone treatment didn’t appear to negatively affect the N-95 filtration material.
But it did damage the elastic materials used to hold the masks in place. While the elastic headbands could be removed from the masks during ozone disinfection, removing and replacing them on a large scale may make the treatment technique impractical. Otherwise, however, ozone may offer an alternative technique for disinfecting other types of PPE.
“Ozone would be a viable method for hospitals and other organizations to disinfect garments, goggles, and gloves,” Finn added. “It is inexpensive to produce, and we hope that by sharing information about what we’ve found, healthcare facilities will be able to consider it as an option, particularly in low-resource areas of the world.”
Beyond those already mentioned, the research involved Emmeline Blanchard from the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University; Justin Lawrence, Taekyu Joo, and Britney Schmidt from the Georgia Tech School of Earth and Atmospheric Sciences; Minghao Xu from the Georgia Tech School of Chemistry and Biochemistry; and Jeffrey Noble from the Parker Petit Institute for Bioengineering and Bioscience.
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]]>Fractionation of crude oil mixtures using heat-based distillation is a large-scale, energy-intensive process that accounts for nearly 1% of the world’s energy use: 1,100 terawatt-hours per year (TWh/yr), which is equivalent to the total energy consumed by the state of New York in a year. By substituting the low-energy membranes for certain steps in the distillation process, the new technology might one day allow implementation of a hybrid refining system that could help reduce carbon emissions and energy consumption significantly compared to traditional refining processes.
“Much in our modern lives comes from oil, so the separation of these molecules makes our modern civilization possible,” said M.G. Finn, professor and chair of Georgia Tech’s School of Chemistry and Biochemistry. Finn also holds the James A. Carlos Family Chair for Pediatric Technology. “The scale of the separation required to provide the products we use is incredibly large. This membrane technology could make a significant impact on global energy consumption and the resulting emissions of petroleum processing.”
Reported in the July 17 issue of the journal Science, the paper is believed to be the first report of a synthetic membrane specifically designed for the separation of crude oil and crude-oil fractions. Additional research and development will be needed to advance this technology to industrial scale.
Membrane technology is already widely used in such applications as seawater desalination, but the complexity of petroleum refining has until now limited the use of membranes. To overcome that challenge, the research team developed a novel spirocyclic polymer that was applied to a robust substrate to create membranes able to separate complex hydrocarbon mixtures through the application of pressure rather than heat.
Membranes separate molecules from mixtures according to differences such as size and shape. When molecules are very close in size, that separation becomes more challenging. Using a well-known process for making bonds between nitrogen and carbon atoms, the polymers were constructed by connecting building blocks having a kinked structure to create disordered materials with built-in void spaces.
The team was able to balance a variety of factors to create the right combination of solubility – to enable membranes to be formed by simple and scalable processing – and structural rigidity – to allow some small molecules to pass through more easily than others. Unexpectedly, the researchers found that the materials needed a small amount of structural flexibility to improve size discrimination, as well as the ability to be slightly “sticky” toward certain types of molecules that are found abundantly in crude oil.
After designing the novel polymers and achieving some success with a synthetic gasoline, jet fuel, and diesel fuel mixture, the team decided to try to separate a crude oil sample and discovered that the new membrane was quite effective at recovering gasoline and jet fuel from the complex mixture.
“We were initially trying to fractionate a mixture of molecules that were too similar,” said Ben McCool, a senior research associate at ExxonMobil and one of the paper’s coauthors. “When we took on a more complex feed, crude oil, we got fractionalization that looked like it could have come from a distillation column, indicating the concept’s great potential.”
The researchers worked collaboratively, with polymers designed and tested at Georgia Tech, then converted to 200-nanometer-thick films, and incorporated into membrane modules at Imperial using a roll-to-roll process. Samples were then tested at all three organizations, providing multi-lab confirmation of the membrane capabilities.
“We have the foundational experience of bringing organic solvent nanofiltration, a membrane technology becoming widely used in pharmaceuticals and chemicals industries, to market,” said Andrew Livingston, professor of chemical engineering at Imperial. “We worked extensively with ExxonMobil and Georgia Tech to demonstrate the scalability potential of this technology to the levels required by the petroleum industry.”
The research team created an innovation pipeline that extends from basic research all the way to technology that can be tested in real-world conditions.
“We brought together basic science and chemistry, applied membrane fabrication fundamentals, and engineering analysis of how membranes work,” said Ryan Lively, associate professor and John H. Woody faculty fellow in Georgia Tech’s School of Chemical and Biomolecular Engineering. “We were able to go from milligram-scale powders all the way to prototype membrane modules in commercial form factors that were challenged with real crude oil – it was fantastic to see this innovation pipeline in action.”
ExxonMobil’s relationship with Georgia Tech goes back nearly 15 years and has produced innovations in other separation technologies, including a new carbon-based molecular sieve membrane that could dramatically reduce the energy required to separate a class of hydrocarbon molecules known as alkyl aromatics.
“Through collaboration with strong academic institutions like Georgia Tech and Imperial, we are constantly working to develop the lower-emissions energy solutions of the future," said Vijay Swarup, vice president of research and development at ExxonMobil Research and Engineering Company.
In addition to Finn, Livingston, Lively, and McCool, the paper’s authors include Kirstie Thompson and Ronita Mathias, Georgia Tech graduate students who are co-first authors; Daeok Kim, Jihoon Kim, Irene Bechis, Andrew Tarzia, and Kim Jelfs of Imperial; and Neel Rangnekar, J.R. Johnson, and Scott Hoy of ExxonMobil.
CITATION: Kirstie Thompson, et al., “N-Aryl Linked Spirocyclic Polymers for Membrane Separations of Complex Hydrocarbon Mixtures” (Science 2020). https://science.sciencemag.org/content/369/6501/310
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]]>Researchers at the Georgia Tech Research Institute (GTRI) have built two prototype chambers to evaluate PPE disinfection using different sources of UV-C light: mercury vapor lamps and light-emitting diodes (LEDs). They used the prototypes to evaluate different power levels and disinfection times with a variety of face shields and face masks used to protect workers from the coronavirus.
“There are tradeoffs in terms of cost, lifetime, and potential heat generated,” said T. Robert Harris, a GTRI research engineer. “We wanted to evaluate these issues so that when others use UV-C for disinfecting PPE, they will have information to make good choices.”
The goal was to provide disinfection chambers as small as possible to allow portability. The chambers were built to accommodate face masks and at least one face shield – a curved sheet of clear plastic that covers the entire face and protects against large droplets that could contain coronavirus. The portability of the chambers could allow them to be used anywhere PPE disinfection is needed.
“We wanted a box that would fit on an ambulance or in a police car so that public service staff who are coming into contact with a lot of people on a regular basis would be able to disinfect their PPE,” Harris said. “This method offers an advantage over chemical disinfection because it doesn’t require drying time or risk of chemical absorption.”
Originally, the project aimed at disinfecting PPE while it was being worn by having healthcare workers walk past an ultraviolet source while going from one hospital room to another. That idea was dropped because the wavelengths needed to inactivate the virus – 280 nanometers – can cause skin and eye damage in humans.
For that reason, the prototype portable disinfection chambers include a safety interlock to prevent the door from being opened while the UV light is on. Disinfection takes about eight minutes, depending on the intensity of UV emissions, which vary by the lighting source. The chambers are designed to be cleaned between uses.
“Healthcare workers would put their face masks and face shields into the box, close the lid, and set the timer,” Harris explained. “They would swap out one set of PPE while the other set was being disinfected.”
Ultraviolet light can damage plastic items, but Harris and his colleagues didn’t attempt to evaluate how many disinfection cycles the PPE could withstand. “You would expect UV to ultimately degrade PPE materials in the same way that sunlight slowly degrades polymer materials,” he said.
The research team designed the chambers to provide the level of UV exposure that earlier studies had shown would inactivate the closely related SARs-CoV virus by damaging its outer shell and RNA. The researchers did not attempt to evaluate the ability of the UV light to inactivate the SARS-Cov-2 virus that causes Covid-19.
Other engineering considerations included the need for cooling the UV sources, providing consistent exposure of the PPE to UV light using reflective walls in the chambers, and protecting the mercury vapor lamps from damage during use.
Ultraviolet light is now used in water and wastewater sanitation, food disinfection, killing pathogens in HVAC systems, and other purposes. Because of the growing number of applications, finding enough mercury vapor lamps and LED sources was a challenge for the research program, which was funded by GTRI’s independent research and development program.
Harris hopes the project will encourage others to further develop UV-based portable disinfection systems to supplement other methods for protecting people who encounter the coronavirus.
“This work is part of a realization that multiple tools – including handwashing, surface disinfection, face masks, UV disinfection, social distancing, and other steps – are important and much more powerful when done together,” he said. “We should all use every tool we have at our disposal to combat this virus and really think about things carefully to break every link in the chain of contagious transmission.”
Beyond Harris, the research team included Roger Campbell, Ashton Hattori, Eric Brown, Christopher Hollis, Max Schureck, Howard Atchley, John Stone, Michael Grady, and Benjamin Yang.
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]]>Researchers at the Georgia Institute of Technology have produced what may be the first kinematic study of how this amazing arachnid stores enough energy to produce acceleration of 1,300 meters/second2 – 100 times the acceleration of a cheetah. That acceleration produces velocities of 4 meters per second and subjects the spider to forces of approximately 130 Gs, more than 10 times what fighter pilots can withstand without blacking out.
The Peruvian spider and its cousins stand out among arachnids for their ability to make external tools – in this case, their webs – and use them as springs to create ultrafast motion. Their ability to hold a ready-to-launch spring for hours while waiting for an approaching mosquito suggests yet another amazing tool: a latch mechanism to release the spring.
“Unlike frogs, crickets, or grasshoppers, the slingshot spider is not relying on its muscles to jump really quickly,” said Saad Bhamla, an assistant professor in Georgia Tech’s School of Chemical and Biomolecular Engineering who studies ultrafast organisms. “When it weaves a new web every night, the spider creates a complex, three-dimensional spring. If you compare this natural silk spring to carbon nanotubes or other human-made materials in terms of power density or energy density, it is orders of magnitude more powerful.”
The study, supported by the National Science Foundation and National Geographic Society Foundation, was published August 17 in the journal Current Biology.
Understanding how web silk stores energy could potentially provide new sources of power for tiny robots and other devices, and lead to new applications for the robust material, the researchers say.
Slingshot spiders, known by the scientific genus name Theridiosomatid, build three-dimensional conical webs with a tension line attached to the center. The Peruvian member of that spider family, which is about 1 millimeter in length, pulls the tension line with its front legs to stretch the structure while holding on to the web with its rear legs. When it senses a meal within range, the spider launches the web and itself toward a fly or mosquito.
If the launch is successful, the spider quickly wraps its meal in silk. If the spider misses, it simply pulls the tension line to reset the web for the next opportunity.
“We think this approach probably gives the spider the advantage of speed and surprise, and perhaps even the effect of stunning the prey,” noted Symone Alexander, a postdoctoral researcher in Bhamla’s lab. “The spiders are tiny, and they are going after fast-flying insects that are larger than they are. To catch one, you must be much, much faster than they are.”
Slingshot spiders were described in a 1932 publication, and more recently by Jonathan Coddington, now a senior research entomologist at the Smithsonian Institution. Bhamla has an interest in fast-moving but small organisms, so he and Alexander arranged a trip to study the catapulting creature using ultrafast cameras to measure and record the movement.
“We wanted to understand these ultrafast movements because they can force our perspective to change from thinking about cheetahs and falcons as the only fast animals,” Bhamla said. “There are many very small invertebrates that can achieve fast movement through unusual structures. We really wanted to understand how these spiders achieve that amazing acceleration.”
The researchers traveled six hours by boat from Puerto Maldonado to the Tambopata Research Center. There is no electricity in the area, so nights are very dark. “We looked up and saw a tiny red dot,” Bhamla recalled. “We were so far away from the nearest light that the dot turned out to be the planet Mars. We could also see the Milky Way so clearly.”
The intense darkness raises the question of how the spider senses its prey and determines where to aim itself. Bhamla believes it must be using an acoustic sensing technique, a theory supported by the way the researchers tricked the spider into launching its web: They simply snapped their fingers.
Beyond sensing in the dark, the researchers also wondered how the spider triggers release of the web. “If an insect gets within range, the spider releases a small bundle of silk that it has created by crawling along the tension line,” Alexander said. “Releasing the bundle controls how far the web flies. Both the spider and web are moving backward.”
Another mystery is how the spider patiently holds the web while waiting for food to fly by. Alexander and Bhamla estimated that stretching the web requires at least 200 dynes, a tremendous amount of energy for a tiny spider to generate. Holding that for hours could waste a lot of energy.
“Generating 200 dynes would produce tremendous forces on the tiny legs of the spider,” Bhamla said. “If the reward is a mosquito at the end of three hours, is that worth it? We think the spider must be using some kind of trick to lock its muscles like a latch so it doesn’t need to consume energy while waiting for hours.”
Beyond curiosity, why travel to Peru to study the creature? “The slingshot spider offers an example of active hunting instead of the passive, wait for an insect to collide into the web strategy, revealing a further new functionality of spider silk,” Bhamla said. “Before this, we hadn’t thought about using silk as a really powerful spring.”
Another unintended benefit is changing attitudes toward spiders. Prior to the study, Alexander admits she had a fear of spiders. Being surrounded by slingshot spiders in the Peruvian jungle – and seeing the amazing things they do – changed that.
“In the rainforest at night, if you shine your flashlight, you quickly see that you are completely surrounded by spiders,” she said. “In my house, we don’t kill spiders anymore. If they happen to be scary and in in the wrong place, we safely move them to another location.”
Alexander and Bhamla had hoped to return to Peru this summer, but those plans were cut short by the coronavirus. They’re eager to continue learning from the spider.
“Nature does a lot of things better than humans can do, and nature has been doing them for much longer,” she said. “Being out in the field gives you a different perspective, not only about what nature is doing, but also why that is necessary.”
This research was supported by the National Science Foundation (NSF) through award 1817334 and CAREER 1941933, by the National Geographic Foundation through NGS-57996R-19, and by the Eckert Postdoctoral Research Fellowship from the Georgia Tech School of Chemical and Biomolecular Engineering. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the funding organizations.
CITATION: Symone L.M. Alexander and M. Saad Bhamla, “Ultrafast launch of slingshot spiders using conical silk webs” (Current Biology, 2020). https://doi.org/10.1016/j.cub.2020.06.076
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]]>By learning from a groundbreaking cancer treatment strategy based on a recent Nobel Prize-winning discovery, researchers at the Georgia Institute of Technology and University of Missouri developed a new microgel drug delivery method that could extend the effectiveness of pancreatic islet transplantations — from several years to possibly the entire lifespan of a recipient.
Working across multidisciplinary teams using an animal model, the labs of Professors Andrés García at Georgia Tech and Haval Shirwan at the University of Missouri have developed a new biomaterial microgel that could deliver safer, smaller, and more cost-effective dosages of an immune-suppressing protein that could lead to better long-term acceptance of islet transplantations within the body.
The study was published August 28, 2020, in the journal Science Advances. The research was led by Maria Coronel, a postdoctoral fellow in the lab of García, the Parker H. Petit Chair and executive director of the Petit Institute for Bioengineering and Bioscience. García is also a Regents Professor in the George W. Woodruff School of Mechanical Engineering.
In 2018, the Nobel Prize for medicine was awarded for discovering how cancer cells send molecular signals to suppress immune response, thus hiding and protecting those cancer cells from the body’s immune system. Researchers soon developed pioneering treatment methods to signal and “turn on” the immune system (such as T cells) so the invading cancer would once again be recognized, allowing a patient’s own immune system to more effectively eliminate their cancer cells.
“The work we are doing is taking a page from that discovery and using immunotherapy in the opposite sense used by cancer treatments to control and ‘turn off’ an immune response to transplant a graft,” Coronel said. “When you get a transplant, like an islet transplant or organ transplant, even if it’s matched, you will have an immune response to that graft, and your immune system will recognize it as non-self and will try to reject and attack the site of the graft.”
After islet transplant surgery, traditional postoperative treatments use immune-suppressing systemic drugs that affect the entire body, and can be toxic — creating numerous, unwelcome side effects, whose severity often limits the number of candidates for islet and other organ transplants.
“A unique aspect of our method is that we have greatly reduced the dosage needed, which will significantly reduce or eliminate side effects currently caused by today’s systemic drug treatments,” said Coronel.
The research team developed a new “immune-acceptance” method, which inserts an engineered biomaterial — in this case a microgel — with the islets at the time of the transplantation. The microgels, which resemble clusters of micro-sized fish eggs, held and delivered a protein (SA-PD-L1) to a specific transplant area that successfully signaled the immune system to hold back an immune response, protecting a transplanted islet graft from being rejected. This locally delivered molecular signal, using SA-PD-L1, was designed to quietly suppress any immune response and was effective for up to 100 days with no additional systemic immune-suppressing drug intervention.
“We wanted to use PD-L1 for the prevention of allogeneic islet graft rejection by simulating the way tumor cells use this molecule to evade the immune system, but without resorting to gene therapy,” said Shirwan, professor of child health and molecular microbiology and immunology at the University of Missouri School of Medicine.
To achieve this goal, Shirwan worked with Esma Yolcu, professor of child health, also at the University of Missouri School of Medicine. Both were previously at the University of Louisville, where they generated the SA-PD-L1, a novel form of the molecule that can be positionally displayed on the surface of islet grafts or microgels for delivery to the graft site.
“Microgels presenting SA-PD-L1 represent an important technological development that has potential not only for the treatment of type 1 diabetes, but also other autoimmune diseases and various transplant types,” Shirwan said.
In addition to engineering this specific biomaterial microgel, the team tested its lifespan durability and dosage release possibilities. They also looked at its longer-term effects on both the graft and the immune response and function of the recipient — evaluating its long-term biocompatibility potential.
“One of the major goals in the diabetes field over the past two decades has been to allow the immune-acceptance of grafts and avoid the toxic drugs used to induce immune suppression, which affect the entire body,” García said.
“Generally speaking, organ transplantation is very successful at dealing with a variety of chronic conditions. These are very exciting results as proof of principle that demonstrate this engineered biomaterial and procedure may provide a platform technology that is applicable to other transplantation settings and may enlarge the pool of candidates who can safely receive transplants.”
These researchers also coauthored the study: Karen E. Martin, Michael D. Hunckler, Graham Barber, Eric B. O’Neill, Juan D. Medina, Claire A. McClain, Jessica D. Weaver, Hong S. Lim, Peng Qiu, and Edward A. Botchwey from the Georgia Institute of Technology; Enrico Opri from Emory University; and Lalit Batra from the University of Louisville.
The research was funded by the National Institutes of Health (R21EB020107, R01AI121281, U01AI132817, and S10OD016264), the National Institute of General Medical Sciences (NIGMS) Biotechnology Training Program on Cell and Tissue Engineering (T32GM008433), the Juvenile Diabetes Research Foundation Postdoctoral Fellowships, and a National Science Foundation Graduate Fellowship. Any findings, conclusions, and recommendations are those of the authors and not necessarily of the funding agencies.
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]]>The modular Georgia Tech mask combines a barrier filtration material with a stretchable fabric to hold it in place. Prototypes made for testing use hook and eye fasteners on the back of the head to keep the masks on, and include a pocket for an optional filter to increase protection. After 20 washings, the prototypes have not shrunk or lost their shape.
“If we want to reopen the economy and ask people to go back to work, we need a mask that is both comfortable and effective,” said Sundaresan Jayaraman, the Kolon Professor in Georgia Tech’s School of Materials Science and Engineering. “We have taken a science-based approach to designing a better mask, and we are very passionate about getting this out so people can use it to help protect themselves and others from harm.”
The fundamental flaw in existing reusable cloth masks is that they — unlike N95 respirators, which are fitted for individual users — leak air around the edges, bypassing their filtration mechanism. That potentially allows virus particles, both large droplets and smaller aerosols, to enter the air breathed in by users, and allows particles from infected persons to exit the mask.
The leakage problem shows up in complaints about eyeglasses fogging up as exhaled breath leaks around the nose, making people less likely to wear them. The fit problem can also be seen in constant adjustments made by wearers, who could potentially contaminate themselves whenever they touch the masks after touching other surfaces.
To address the leakage challenge, Jayaraman and principal research scientist Sungmee Park created a two-part mask that fastens behind the head like many N95 respirators. The front part — the barrier component — contains the filtration material and is contoured to fit tightly while allowing space ahead of the nose and mouth to avoid breathing restrictions and permit unrestricted speech. Made from the kind of moisture-wicking material used in athletic clothing, it includes a pocket into which a filter can be inserted to increase the filtration efficiency and thereby increase protection. The washable fabric filter is made of a blend of Spandex and polyester.
The second part of the mask is fashioned from stretchable material. The stretchable part, which has holes for the ears to help position the mask, holds the front portion in place and fastens with conventional hook and eyelet hardware, a mechanism that has been used in clothing for centuries.
“We want people to be able to get the mask in the right place every time,” Jayaraman said. “If you don’t position it correctly and easily, you are going to have to keep fiddling with it. We see that all the time on television with people adjusting their masks and letting them drop below their noses.”
Beyond controlling air leakage, designing a better mask involves a tradeoff between filtration effectiveness and how well users can breathe. If a mask makes breathing too difficult, users will simply not use it, reducing compliance with masking requirements.
Many existing mask designs attempt to increase filtration effectiveness by boosting the number of layers, but that may not be as helpful as it might seem, Park said. “We tested 16 layers of handkerchief material, and as we increased the layers, we measured increased breathing resistance,” she said. “While the breathing resistance went up, the filtration did not improve as much as we would have expected.”
“Good filtration efficiency is not enough by itself,” said Jayaraman. “The combination of fit, filtration efficiency, and staying in the right place make for a good mask.”
The stretchable part of the mask is made from knitted fabric — a Spandex/Lyocell blend — to allow for stretching around the head and under the chin. The researchers used a woven elastic band sewn with pleats to cover the top of the nose.
The researchers made their mask prototypes from synthetic materials instead of cotton. Though cotton is a natural material, it absorbs moisture and holds it on the face, reducing breathability, and potentially creating a “petri dish” for the growth of microbes.
“Masks have become an essential accessory in our wardrobe and add a social dimension to how we feel about wearing them,” Park said. So, the materials chosen for the mask come in a variety of colors and designs. “Integrating form and function is key to having a mask that protects individuals while making them look good and feel less self-conscious,” Jayaraman said.
The work of Jayaraman and Park didn’t begin with the Covid-19 pandemic. They received funding 10 years ago from the Centers for Disease Control and Prevention to study face masks during the avian influenza outbreak. Since then Jayaraman has been part of several National Academy of Medicine initiatives to develop recommendations for improved respiratory protection.
Covid-19 dramatically increased the importance of using face masks because of the role played by asymptomatic and pre-symptomatic exposure from persons who don’t know they are infected, Jayaraman said. While the proportion of aerosol contributions to transmission is still under study, they likely increase the importance of formfitting masks that don’t leak.
Jayaraman and Park have published their recommendations in The Journal of The Textile Institute, and will make the specifications and patterns for their mask available to individuals and manufacturers. The necessary materials can be obtained from retail fabric stores, and the instructions describe how to measure for customizing the masks.
“There is so much misinformation about what face masks can do and cannot do,” Jayaraman said. “Being scientists and engineers, we want to put out information backed by science that can help our community reduce the harm from SARS-CoV-2.”
Link to plans, patterns and specifications for this mask
CITATION: Sungmee Park and Sundaresan Jayaraman, “From containment to harm reduction from SARS-CoV-2: a fabric mask for enhanced effectiveness, comfort, and compliance.” (The Journal of The Textile Institute, 2020) https://doi.org/10.1080/00405000.2020.1805971
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]]>Based on focused electron beam-induced processing (FEBID) techniques, the work could allow production of 2D/3D complex nanostructures and functional nanodevices useful in quantum communications, sensing, and other applications. For oxygen-containing materials such as graphene oxide, etching can be done without introducing outside materials, using oxygen from the substrate.
“By timing and tuning the energy of the electron beam, we can activate interaction of the beam with oxygen in the graphene oxide to do etching, or interaction with hydrocarbons on the surface to create carbon deposition,” said Andrei Fedorov, professor and Rae S. and Frank H. Neely Chair in the George W. Woodruff School of Mechanical Engineering at the Georgia Institute of Technology. “With atomic-scale control, we can produce complicated patterns using direct write-remove processes. Quantum systems require precise control on an atomic scale, and this could enable a host of potential applications.”
The technique was described August 7 in the journal ACS Applied Materials & Interfaces. The work was supported by the U.S. Department of Energy Office of Science, Basic Energy Sciences. Coauthors included researchers from Pusan National University in South Korea.
Creation of nanoscale structures is traditionally done using a multistep process of photoresist coating and patterning by photo- or electron beam lithography, followed by bulk dry/wet etching or deposition. Use of this process limits the range of functionalities and structural topologies that can be achieved, increases the complexity and cost, and risks contamination from the multiple chemical steps, creating barriers to fabrication of new types of devices from sensitive 2D materials.
FEBIP enables a material chemistry/site-specific, high-resolution multimode atomic scale processing and provides unprecedented opportunities for “direct-write,” single-step surface patterning of 2D nanomaterials with an in-situ imaging capability. It allows for realizing a rapid multiscale/multimode “top-down and bottom-up” approach, ranging from an atomic scale manipulation to a large-area surface modification on nano- and microscales.
“By tuning the time and the energy of the electrons, you can either remove material or add material,” Fedorov said. “We did not expect that upon electron exposure of graphene oxide we would start etching patterns.”
With graphene oxide, the electron beam introduces atomic scale perturbations into the 2D-arranged carbon atoms and uses embedded oxygen as an etchant to remove carbon atoms in precise patterns without introduction of a material into the reaction chamber. Fedorov said any oxygen-containing material might produce the same effect. “It’s like the graphene oxide carries its own etchant,” he said. “All we need to activate it is to ‘seed’ the reaction with electrons of appropriate energy.”
For adding carbon, keeping the electron beam focused on the same spot for a longer time generates an excess of lower-energy electrons by interactions of the beam with the substrate to decompose the hydrocarbon molecules onto the surface of the graphene oxide. In that case, the electrons interact with the hydrocarbons rather than the graphene and oxygen atoms, leaving behind liberated carbon atoms as a 3D deposit.
“Depending on how many electrons you bring to it, you can grow structures of different heights away from the etched grooves or from the two-dimensional plane,” he said. “You can think of it almost like holographic writing with excited electrons, substrate and adsorbed molecules combined at the right time and the right place.”
The process should be suitable for depositing materials such as metals and semiconductors, though precursors would need to be added to the chamber for their creation. The 3D structures, just nanometers high, could serve as spacers between layers of graphene or as active sensing elements or other devices on the layers.
“If you want to use graphene or graphene oxide for quantum mechanical devices, you should be able to position layers of material with a separation on the scale of individual carbon atoms,” Fedorov said. “The process could also be used with other materials.”
Using the technique, high-energy electron beams can produce feature sizes just a few nanometers wide. Trenches etched in surfaces could be filled with metals by introducing metal atoms containing precursors.
Beyond simple patterns, the process could also be used to grow complex structures. “In principle, you could grow a structure like a nanoscale Eiffel Tower with all the intricate details,” Fedorov said. “It would take a long time, but this is the level of control that is possible with electron beam writing.”
Though systems have been built to use multiple electron beams in parallel, Fedorov doesn’t see them being used in high-volume applications. More likely, he said, is laboratory use to fabricate unique structures useful for research purposes.
“We are demonstrating structures that would otherwise be impossible to produce,” he said. “We want to enable the exploitation of new capabilities in areas such as quantum devices. This technique could be an imagination enabler for interesting new physics coming our way with graphene and other interesting materials.”
In addition to Fedorov, the research team included Songkil Kim, SungYeb Jung, Jaekwang Lee, and Seokjun Kim from Pusan National University in South Korea.
This research was supported primarily by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under award no. DE-SC0010729, and by the National Research Foundation of Korea grant MSIT no. 2019R1C1C1010556 funded by the Korean government. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the sponsoring organizations.
CITATION: Songkil Kim, et al., “High-Resolution Three-Dimensional Sculpting of Two-Dimensional Graphene Oxide by E‑Beam Direct Write.” (ACS Applied Materials & Interface, 2020.) https://doi.org/10.1021/acsami.0c11053
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]]>The researchers demonstrated for the first time a multifunctional, magnetically responsive origami system, possessing distributed, untethered control capabilities. The untethered magnetic actuation separates the power source and controller out of the system, allowing scalable applications.
Researchers foresee that this actuation solution can be applied locally and remotely on complex origami assemblies. The actuation strategy enables a myriad of new applications, ranging from morphing robotics and satellites to biomedical devices.
“By distributively integrating the programmed magnetic soft materials into the bi-stable origami assembly, the magnetic actuation provides independent control of the folding and unfolding of each unit cell with instantaneous shape locking, which enables various robotic motion for functions such as tunable physical properties and configurable electronics for digital computing,” said principal investigator Ruike (Renee) Zhao, an assistant professor in the Department of Mechanical and Aerospace Engineering at Ohio State.
The research, "Untethered control of functional origami microrobots with distributed actuation," was reported Sept. 14 in the journal Proceedings of the National Academy of Sciences. The work was sponsored by the National Science Foundation (NSF).
Researchers have explored for decades how to leverage origami folding techniques in advanced engineering applications, such as morphing structures and devices. However, most actuation methods require physical bonds to external stimuli and lead to excessive wiring to provide the driving force for origami folding.
The new, untethered system is free from those rigid and often relatively bulky power sources, allowing faster speed and distributed actuation of the multifunctional structure.
To demonstrate this, researchers constructed a system of magnetic-responsive materials in a cylindrical origami pattern that consists of identical triangular panels known as a Kresling pattern. This pattern allows the cylinder’s walls to buckle under axial or torsional load.
“The Kresling pattern offers a very rich design space, which was crucial in coupling its mechanical response with magnetically responsive materials to achieve on-demand, untethered actuation, including our multifunctional origami for digital computing,” said Glaucio Paulino, professor and Raymond Allen Jones Chair in the Georgia Tech School of Civil and Environmental Engineering.
By controlling the magnetic field, researchers were able to control the direction, intensity, and speed of the material’s folding and deployment. In the tests, researchers achieved untethered actuation as fast as one tenth of a second with instantaneous shape locking.
Next, researchers attached a magnetized plate to each of the Kresling unit cells. This allowed them to utilize a two-dimensional magnetic field to actuate the unit cells simultaneously or independently by using different magnetic torques of the plates and distinct geometric-mechanical properties of each unit cell.
“The multi-unit Kresling assembly is an origami robot in which the bi-stable folding and unfolding create robotic motion. It can passively sense and actively respond to the external environment. By integrating electronic circuits into the origami robot, it further enables intelligent autonomous robots with integrated actuation, sensing, and decision making,” Zhao said. “For example, the external pressure or forces that act on the robot will trigger the passive folding of the robot, indicating the presence of an obstacle. The robot can then actively unfold itself and decide the next move.”
The untethered magnetic control pushes the boundary of the application of origami systems, which could lead to solutions of next-generation biomimetic soft robots and robotic systems for advanced engineering applications.
“We anticipate that the reported magnetic origami system is applicable beyond the bounds of this work, including future origami-inspired robots, morphing mechanisms, biomedical devices, and outer space structures,” Paulino said.
This research was supported by Prof. Zhao’s two recent NSF Awards from the Mechanics of Materials and Structures program (NSF Award #1943070, #1939543) and Ohio State’s Institute of Material Research. The authors at Georgia Tech acknowledge NSF (Award #1538830) and the Raymond Allen Jones Chair. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
- Written by The Ohio State University
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]]>Looking like any other small vial of clear liquid, these programmable drugs would communicate directly with our biological systems, dynamically responding to the information flowing through our bodies to automatically deliver proper doses where and when they are needed. These future medicines might even live inside us throughout our lives, fighting infection, detecting cancer and other diseases, essentially becoming a therapeutic biological extension of ourselves.
We are years away from that, but the insights gained from research in Gabe Kwong’s lab are moving us closer with the development of ‘enzyme computers’ — engineered bio-circuits designed with biological components, with the capacity to expand and augment living functions.
“The long-term vision is this concept of programmable immunity,” said Kwong, associate professor in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory University, who partnered with fellow researcher Brandon Holt on the paper, “Protease circuits for processing biological information,” published Oct. 6 in the journal Nature Communications. The research was sponsored by the National Institutes of Health.
The story of this paper begins two years ago when, Holt said, “our lab has a rich history of developing enzyme-based diagnostics; eventually we started thinking about these systems as computers, which led us to design simple logic gates, such as AND gates and OR gates. This project grew organically and we realized that there were other devices we can build, like comparators and analog-digital convertors. Eventually this led to the idea of taking an analog-to-digital converter and using that to digitize bacterial activity.”
Ultimately, they assembled cell-free bio-circuits that can combine with bacteria-infected blood, “with the basic idea that it would quantify the bacterial infection — the number of bacteria — then calculate and release a selective drug dose, essentially in real time,” said Holt, a Ph.D. student in Kwong’s Laboratory for Synthetic Immunity and lead author of the paper.
The researchers sought to construct bio-circuits that use protease activity to process biological information under a digital or analog framework (proteases are enzymes that break down proteins into smaller polypeptides and amino acids). The team built its analog-to-digital converter with a tiny device, made only of biological materials, that changed signals from bacteria into ones and zeroes. Then, the circuit used these numbers to choose the proper dosage of drugs needed to kill the bacteria without overdosing.
That’s the traditional approach — bio-circuits digitizing molecular signals, allowing operations to be carried out by Boolean logic. The second part of the team’s new paper takes a more nuanced approach, with a focus on analog circuits as opposed to digital. “We treat protease activity as multi-valued, signals between one and zero,” Holt said.
That multi-valued approach led to yet another idea, and ultimately to the bigger picture of analog bio-circuits.
“We got tempted by this idea of fuzzy logic, where you can think about what happens if there’s a signal between zero and one,” he added. “That’s more like an analog circuit. We were really inspired by this concept, so we decided to build analog bio-circuits with the same basic materials as before — proteases and peptides. And we were able to solve a mathematical oracle problem, Learning Parity with Noise.”
The ability to process information from the biomolecular environment with an analog framework is critical, according to Kwong.
“Fuzzy logic is interesting because biology doesn’t think in zeroes and ones,” he said. “Biology operates as a spectrum. So if you think about enzymatic activity, it’s never just on and off. It’s on, and the activity can be anywhere between zero and one. So the long term goal is to recognize that biology is not as simple as a digital electronic circuit. You actually need some capacity to work with analog signals.”
This work was funded by an NIH Director’s New Innovator Award (Award No. DP2HD091793) as well as an R01 from the NCI (GR10003709). Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the NIH.
Competing interests: Gabe Kwong is co-founder of and consultant to Glympse Bio, which is developing products related to the research described in this paper. This study could affect his personal financial status. The terms of this arrangement have been reviewed and approved by Georgia Tech in accordance with its conflict of interest policies. Holt and Kwong are listed as inventors on a patent application pertaining to the results of the paper. The patent applicant is the Georgia Tech Research Corporation. The application 24 number is PCT/US19/051833. The patent is currently pending/published (publication no. WO 25 2020/061257). The biological analog-to-digital converter and the analog protease circuits are covered in the patent.
CITATION: Brandon Holt, Gabe Kwong. “Protease circuits for processing biological information.” (Nature Communications, 2020) (https://www.nature.com/articles/s41467-020-18840-8)
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]]>Using large-scale computer simulations, researchers at the Georgia Institute of Technology have now mapped out the surprising behavior and mechanics of these complex particle-solvent systems, learning how the “soft and squishy” particles deform, swell, de-swell, and penetrate each other as they respond to compression. The findings could help guide the design of microgel-based applications with unique and useful properties.
“We wanted to understand broadly what happens to these particles if you put them together and start compressing them,” said Alexander Alexeev, professor and Anderer Faculty Fellow in Georgia Tech’s George W. Woodruff School of Mechanical Engineering. “Unlike rigid particles that fill the available space and then stop compressing, these particles have multiple processes that can work in parallel inside the suspension. Microgels can change shape, shrink, and penetrate one another. We found that these processes play a varying role when you increase the particle number density and compress them enough.”
Findings of the study were reported October 19 in the journal Proceedings of the National Academy of Sciences. The research was supported by the National Science Foundation (NSF) and the MCIU/AEI/FEDER EU, and simulations utilized the NSF’s Extreme Science and Engineering Discovery Environment.
Using mesoscale computer simulations, the researchers studied the behavior of compressed suspensions consisting of shape-shifting microgels with different architectures at a variety of packing fractions and solvent conditions. They found that under compression, the “fluffy” microgels — which resemble microscopic sponges with polymer threads extending from them — change shape and shrink, with limited interpenetration among particles.
“You can use their softness and the fact that they change shape to pack them even more,” said Alberto Fernandez-Nieves, ICREA Professor in the Department of Condensed Matter Physics at the University of Barcelona and adjunct professor in Georgia Tech’s School of Physics. “There are a variety of mechanisms to pack them into an available volume, and these mechanisms may play a different role depending on the situation. Until this study, we didn’t quite know how the microgels could be packed together beyond random close packing.”
Their ability to release solvent allows the microgels to shrink and deform, unlike hard particles in regular colloidal suspensions. In addition, the polymer threads allow them to interpenetrate and overlap to pack more particles into a given space. The microgel particles range in size from 50 nanometers up to as much as 10 microns in diameter. In their simulations, Alexeev, Fernandez-Nieves, and recent Ph.D. graduate Svetoslav Nikolov studied suspensions containing about a hundred microgel particles.
“Their compressibility is a new ingredient that is not present in other soft particles, and it can bring about the fascinating and unique aspects of these microgel systems,” said Fernandez-Nieves. “This study gives us information we need to exploit this softness to achieve things we wouldn’t be able to do otherwise.”
The simulations provided information about the effects of variables such as solvent type and degree of compression on the mechanical properties of the microgels in the suspension.
“If you look at the mechanical properties of the suspension in different solvents, you see the curves are very different,” Alexeev said. “If they are swollen, they are fluffy and can move around in the suspension. If they expel solvent, they can become almost dry, so the mechanical properties can change dramatically. What we found is surprising and not at all what people expected.”
Among the key fundamental findings is that the mechanical properties of the suspension can be quantified in terms of the single microgel bulk modulus. “It is how these particles compress that determines the material properties of the whole suspension when it is sufficiently concentrated,” Fernandez-Nieves said.
“You can have many different kinds of behavior, but when you scale all the behaviors by the actual compressibility of one microgel, all the behaviors come together,” he added. “That means this quantity seems to be the important one to consider to understand the macroscopic properties of the suspension.”
The researchers used the NSF’s Extreme Science and Engineering Discovery Environment to simulate the microgel systems. While the behavior of ordinary particle-based systems might seem straightforward to study, the compressibility of the microgels coupled with the complexity of the polymer crosslinking made the simulation quite large, Alexeev noted.
“A single particle is already a quite complicated system,” he said. “The computational complexity provided findings that we hope will encourage experimentalists to further explore what these unique systems can do.”
This research was supported by the NSF Faculty Early Career Development (CAREER) Award DMR-1255288, the MCIU/AEI/FEDER, EU (Grant PGC2018-336 097842-B-I00), and NSF Graduate Research Fellowship DGE-1650044. The simulations were performed using the computational resources of the Extreme Science and Engineering Discovery Environment provided through NSF Awards DMR-180038 and DMR-180026. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the funding agencies.
CITATION: Svetoslav V. Nikolov, Alberto Fernandez-Nieves, and Alexander Alexeev, “Behavior and mechanics of dense microgel suspensions” (Proceedings of the National Academy of Sciences, 2020). https://doi.org/10.1073/pnas.2008076117
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]]>The low-noise, solution-processed, flexible organic devices offer the ability to use arbitrarily shaped, large-area photodiodes to replace complex arrays that would be required with conventional silicon photodiodes, which can be expensive to scale up for large-area applications. The organic devices provide performance comparable to that of rigid silicon photodiodes in the visible light spectrum — except in response time.
“What we have achieved is the first demonstration that these devices, produced from solution at low temperatures, can detect as little as a few hundred thousand photons of visible light every second, similar to the magnitude of light reaching our eye from a single star in a dark sky,” said Canek Fuentes-Hernandez, principal research scientist in the School of Electrical and Computer Engineering at the Georgia Institute of Technology. “The ability to coat these materials onto large-area substrates with arbitrary shapes means that flexible organic photodiodes now offer some clear advantages over state-of-the-art silicon photodiodes in applications requiring response times in the range of tens of microseconds.”
The development and performance of large-area, low-noise organic photodiodes are described in the Nov. 6 issue of the journal Science. The research was supported by multiple organizations, including the Office of Naval Research, the Air Force Office of Scientific Research, and the U.S. Department of Energy’s National Nuclear Security Administration.
Organic electronic devices are based on materials fabricated from carbon-based molecules or polymers instead of conventional inorganic semiconductors such as silicon. The devices can be made using simple solution and inkjet printing techniques instead of the expensive and complex processes involved in the manufacturing of conventional electronics. The technology is now widely used in displays, solar cells, and other devices.
The organic photodiodes use polyethylenimine, an amine-containing polymer surface modifier found to produce air-stable, low work-function electrodes in photovoltaic devices developed in the laboratory of Bernard Kippelen, Joseph M. Pettit Professor at Georgia Tech. The use of polyethylenimine was also shown to produce photovoltaic devices with low levels of dark current — the electrical current that flows through a device even in the dark. This meant the materials could be useful in photodetectors for capturing faint signals of visible light.
“Over the years, the dark current levels were reduced so much that measurement equipment had to be redesigned to detect an electronic noise corresponding to a fluctuation of one electron in one millionth of a second,” Fuentes-Hernandez, the paper’s first author, said. “This work reflects sustained team efforts made in the Kippelen group over more than six years and encompasses part of the Ph.D. work of recent graduates Talha Kahn and Wen-Fang Chou. These collective efforts produced the scientific insights needed to demonstrate organic photodiodes with this level of performance.”
One application for the new devices is in pulse oximeters now placed on fingers to measure heart rate and blood oxygen levels. Organic photodiodes may allow multiple devices to be placed on the body and operate with 10 times less light than conventional devices. This could enable wearable health monitors to produce improved physiological information and continuous monitoring without frequent battery changes. Other potential applications include human-computer interfaces such as touchless gesture recognition and controls.
A future application is detection of ionizing radiation by scintillation — a flash of light emitted by a phosphor when struck by a high energy particle. Lowering the level of light that can be detected would improve the sensitivity of the device, allowing it to detect lower levels of radiation. Detecting radiation emitted from vehicles or cargo containers requires a large detector area, which would be easier to make from organic photodiodes than from arrays of silicon photodiodes.
Organic photodiodes could have similar advantages in X-ray equipment, where doctors want to use the smallest level of radiation possible to minimize the dose delivered to the patient. Here again, sensitivity, large area, and flexible form factor should give organic photodiodes an advantage over silicon-based arrays.
“We are working on improving the response time of the photodetector because producing fast photodetectors would enable many additional important applications,” Fuentes-Hernandez said. “There’s a real need to develop photodetector technologies that are more scalable, and one of the motivations of this work is to advance organic technology that we know is cost effective for scaling.”
The organic photodiodes can show electronic noise current values in the tens of femtoampere range and noise equivalent power values of a couple of hundreds of femtowatt. Key performance factors of the organic photodiodes compare well with silicon except in the area of response time, where researchers are working on a hundred-fold improvement to enable future applications.
“Because we use materials that are processed from inks using printing techniques, they are not as ordered as crystalline materials,” Kippelen said. “As a result, the carrier mobility and the velocity of the carriers that can move through these materials are lower, so you can’t get the same fast signals you get with silicon. But for many applications you don’t need picosecond or nanosecond response time.”
For Kippelen, the photodiode work shows the results of a 25-year effort to improve the performance of organic electronic materials. That work, part of Georgia Tech’s Center for Organic Photonics and Electronics, has involved extensive device modeling to understand the basic science, and research to continuously boost performance of the materials.
“Organic thin films absorb light more efficiently than silicon, so the overall thickness you need to absorb that light is very small,” Kippelen said. “Even if you scale their area up, the overall volume of your detector remains small with organics. If you increase the area of a silicon detector, you have a larger volume of materials that at room temperature will generate a lot of electronic noise.”
The photodiodes made in Kippelen’s lab use an active layer just 500 nanometers thick. A gram of the material, roughly the size of a fingertip, could coat the surface of an office desk.
Kippelen hopes the Science paper will help open new doors for organic semiconductors.
“Advances like this will allow us to change the conventional wisdom that switching to organic materials that can lead to scalable devices would mean giving up performance,” he said. “We can’t anticipate all the new applications that could be enabled by this advance.”
In addition to those already mentioned, the research team included Larissa Diniz, Julia Lukens, Felipe A. Larrain, and Victor A. Rodriguez-Toro, all associated with Kippelen’s lab.
This research was supported by the Department of the Navy, Office of Naval Research Awards N00014-15 14-1-0580 and N00014-16-1-2520; through the MURI Center for Advanced Organic Photovoltaics (CAOP); by the Air Force Office of Scientific Research through Award No. FA9550-16-1-0168, the Department of Energy / National Nuclear Security Administration (NNSA) awards DE-NA0002576 through the Consortium for Nonproliferation Enabling Capabilities (CNEC), and award DE-NA0003921 through the Consortium for Enabling Technologies and Innovation. Support also came from the Chilean National Commission for Scientific and Technological Research through the Doctoral Fellowship program ‘‘Becas Chile,’’ Grant 72150387; from the Colombian Administrative Department of Science, Technology, and Innovation through the program Fulbright-Colciencias; from the National Science Foundation through the Research Experiences for Undergraduates program; and from the Brazil Scientific Mobility Program through an Academic Training Opportunities grant.
CITATION: Canek Fuentes-Hernandez, et al., “Large-area low-noise flexible organic photodiodes for detecting faint visible light.” (Science 2020).
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]]>Utilizing data about the properties of more than 200 existing MOFs, the machine learning platform was trained to help guide the development of new materials by predicting an often-essential property: water stability. Using guidance from the model, researchers can avoid the time-consuming task of synthesizing and then experimentally testing new candidate MOFs for their aqueous stability. Already, researchers are expanding the model to predict other important MOF properties.
Supported by the Office of Science’s Basic Energy Sciences program within the U.S. Department of Energy (DOE), the research was reported Nov. 9 in the journal Nature Machine Intelligence. The research was conducted in the Center for Understanding and Control of Acid Gas-Induced Evolution of Materials for Energy (UNCAGE-ME), a DOE Energy Frontier Research Center located at the Georgia Institute of Technology.
“The issue of water stability with MOFs has existed in this field for a long time, with no easy way to predict it,” said Krista Walton, professor and Robert "Bud" Moeller faculty fellow in Georgia Tech’s School of Chemical and Biomolecular Engineering. “Rather than having to do the synthesis and experimentation to figure this out for each candidate MOF, this machine learning model now provides a way to predict water stability given a set of desired features. This will really speed up the process of identifying new materials for specific applications.”
MOFs are a class of porous and crystalline materials that are synthesized from inorganic metal ions or clusters connected to organic ligands. They are known for their easily tunable components that can be customized for specific applications, but the large number of potential combinations makes it difficult to choose MOFs with the desired properties. That’s where artificial intelligence can help.
Machine learning is playing an increasingly important role in materials science, said Rampi Ramprasad, professor and Michael E. Tennenbaum Family Chair in the Georgia Tech School of Materials Science and Engineering and Georgia Research Alliance Eminent Scholar in Energy Sustainability.
“When materials scientists plan the next set of experiments, we use the intuition and insights that we have accumulated from the past,” Ramprasad said. “Machine learning allows us to fully tap into this past knowledge in the most efficient and effective manner. If 200 experiments have already been done, machine learning allows us to exploit all that has been learned from them as we plan the 201st experiment.”
Beyond experimental data, machine learning can also use the results of physics-based simulations. And unlike simulations, the results from machine learning models can be instantaneous. The machine learning algorithm improves as it receives more information, he noted, and both negative and positive results are useful.
“Great discoveries are as important as not-so-exciting discoveries — failed experiments — because machine learning uses both ends of the spectrum to get better at what it does,” Ramprasad said.
The machine learning model used information Walton and her research team had gathered on hundreds of existing MOF materials, both from compounds developed in her own lab and those reported by other researchers. To prepare the information for the model to learn from, she categorized each MOF according to four measures of water stability.
“The couple hundred data points used to build the model represented years of experiments,” Walton said. “I spent basically the first half of my career working to understand this water stability problem with MOFs, so it’s something we have studied extensively.”
Using the model, researchers who are developing new adsorbents and other porous materials for specific applications can now check their proposed formulas to determine the likelihood that a new MOF would be stable in the presence of water. That could be particularly helpful for researchers who don’t have this particular expertise or who don’t have easy access to experimental methods for examining stability.
“The MOF community is diverse, with a variety of subfields. Not everyone has the chemical intuition about which materials’ features lead to good framework stability, and experimental evaluation often requires specialty equipment that many labs may not have or wouldn’t otherwise need for their specific subfield. However, with good predictive models, they wouldn’t necessarily need to develop it to choose a material for a specific application,” Walton said. “This capability potentially opens up this field to a broader group of researchers that could accelerate application development.”
While screening for water stability is important, Ramprasad says it’s just the beginning of the potential benefits from the project. The machine learning model can be trained to predict other properties as long as a sufficient amount of data exists. For instance, the team is already teaching their model about factors affecting methane absorption under varying levels of pressure. In that case, simulations will provide much of the data from which the model will learn.
“We will have a very strong predictor that will tell us if a new MOF would be stable under aqueous conditions and a good candidate for methane uptake,” he said. “What we are doing is creating a universal and scalable machine learning platform that can be trained on new properties. As long as the data is available, the model can learn from it, and make predictions for new cases.”
In addition to those already mentioned, recent Georgia Tech postdoctoral fellow Rohit Batra and Georgia Tech graduate students Carmen Chen and Tania G. Evans were also coauthors on the Nature Machine Intelligence paper.
Ramprasad has experience with machine learning techniques applied to other materials and application spaces, and recently coauthored a review article, “Emerging materials intelligence ecosystems propelled by machine learning,” about a range of artificial intelligence applications in materials science and engineering. Intended to demystify machine learning and to review success stories in the materials development space, it was published, also on Nov. 9, 2020, in the journal Nature Reviews Materials.
In addition to Ramprasad, coauthors on the Nature Review Materials paper included Batra and Le Song, associate professor in the Georgia Tech College of Computing.
This work was supported as part of the Center for Understanding and Control of Acid Gas-Induced Evolution of Materials for Energy (UNCAGE-ME), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences under award no. DE-SC0012577.
CITATION: Rohit Batra, Carmen Chen, Tania G. Evans, Krista S. Walton, and Rampi Ramprasad, “Prediction of water stability in metal–organic frameworks using machine learning.” (Nature Machine Intelligence, 2020) https://doi.org/10.1038/s42256-020-00249-z
CITATION: Rohit Batra, Le Song, and Rampi Ramprasad, “Emerging materials intelligence ecosystems propelled by machine learning.” (Nature Reviews Materials, 2020) https://www.nature.com/articles/s41578-020-00255-y.
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