Scripps researchers collaborate on new technology study using “robotic plankton”
Underwater robots developed by researchers at Scripps Institution of Oceanography at the University of California San Diego offer scientists an extraordinary new tool to study ocean currents and the tiny creatures they transport. Swarms of these underwater robots helped answer some basic questions about the most abundant life forms in the ocean—plankton.
Scripps research oceanographer Jules Jaffe designed and built the miniature autonomous underwater explorers, or M-AUEs, to study small-scale environmental processes taking place in the ocean. The ocean-probing instruments are equipped with temperature and other sensors to measure the surrounding ocean conditions while the robots “swim” up and down to maintain a constant depth by adjusting their buoyancy. The M-AUEs could potentially be deployed in swarms of hundreds to thousands to capture a three-dimensional view of the interactions between ocean currents and marine life.
In a new study published in the Jan. 24 issue of the journal Nature Communications, Jaffe and Scripps biological oceanographer Peter Franks deployed a swarm of 16 grapefruit-sized underwater robots programmed to mimic the underwater swimming behavior of plankton, the microscopic organisms that drift with the ocean currents. The research study was designed to test theories about how plankton form dense patches under the ocean surface, which often later reveal themselves at the surface as red tides.
“These patches might work like planktonic singles bars,” said Franks, who has long suspected that the dense aggregations could aid feeding, reproduction, and protection from predators.
Two decades ago Franks published a mathematical theory predicting that swimming plankton would form dense patches when pushed around by internal waves—giant, slow-moving waves below the ocean surface. Testing his theory would require tracking the movements of individual plankton—each smaller than a grain of rice—as they swam in the ocean, which is not possible using available technology.
Jaffe instead invented “robotic plankton” that drift with the ocean currents, but are programmed to move up and down by adjusting their buoyancy, imitating the movements of plankton. A swarm of these robotic plankton was the ideal tool to finally put Franks’ mathematical theory to the test.
“The big engineering breakthroughs were to make the M-AUEs small, inexpensive, and able to be tracked continuously underwater,” said Jaffe. The low cost allowed Jaffe and his team to build a small army of the robots that could be deployed in a swarm.
Tracking the individual M-AUEs was a challenge, as GPS does not work underwater. A key component of the project was the development by researchers at UC San Diego’s Qualcomm Institute and Department of Computer Science and Engineering of mathematical techniques to use acoustic signals to track the M-AUE vehicles while they were submerged.
During a five-hour experiment, the Scripps researchers along with UC San Diego colleagues deployed a 300-meter (984-foot) diameter swarm of 16 M-AUEs programmed to stay 10-meters (33-feet) deep in the ocean off the coast of Torrey Pines, near La Jolla, Calif. The M-AUEs constantly adjusted their buoyancy to move vertically against the currents created by the internal waves. The three-dimensional location information collected every 12 seconds revealed where this robotic swarm moved below the ocean surface.
The results of the study were nearly identical to what Franks predicted. The surrounding ocean temperatures fluctuated as the internal waves passed through the M-AUE swarm. And, as predicted by Franks, the M-AUE location data showed that the swarm formed a tightly packed patch in the warm waters of the internal wave troughs, but dispersed over the wave crests.
“This is the first time such a mechanism has been tested underwater,” said Franks.
The experiment helped the researchers confirm that free-floating plankton can use the physical dynamics of the ocean—in this case internal waves—to increase their concentrations to congregate into swarms to fulfill their fundamental life needs.
“This swarm-sensing approach opens up a whole new realm of ocean exploration,” said Jaffe. Augmenting the M-AUEs with cameras would allow the photographic mapping of coral habitats, or “plankton selfies,” according to Jaffe.
The research team has hopes to build hundreds more of the miniature robots to study the movement of larvae between marine protected areas, monitor harmful red tide blooms, and to help track oil spills. The onboard hydrophones that help track the M-AUEs underwater could also allow the swarm to act like a giant “ear” in the ocean, listening to and localizing ambient sounds in the ocean.
Learn more: Swarm of Underwater Robots Mimics Ocean Life
The university occupies 2,141 acres (866 ha) near the coast of the Pacific Ocean with the main campus resting on approximately 1,152 acres (466 ha). Established in 1960 near the pre-existing Scripps Institution of Oceanography, UCSD is the seventh oldest of the 10 University of California campuses and offers over 200 undergraduate and graduate degree programs, enrolling about 22,700 undergraduate and 6,300 graduate students. UCSD is one of America’s Public Ivy universities, which recognizes top public research universities in the United States. UC San Diego was ranked 39th among the top universities in the United States, tied for 3rd with UC Davis of the University of California schools, and 9th among public universities by U.S. News & World Report ‘s 2014 rankings.
UC San Diego is organized into six undergraduate residential colleges, five graduate schools, and two professional medical schools. The university operates four research institutes, including the California Institute for Telecommunications and Information Technology, San Diego Supercomputer Center, Scripps Institution of Oceanography, and UC San Diego Health System, and is also affiliated with several regional research centers, such as the Salk Institute, the Sanford-Burnham Medical Research Institute, the Sanford Consortium for Regenerative Medicine, and the Scripps Research Institute. The university also houses two think tanks, the Institute on Global Conflict and Cooperation and Center for Comparative Immigration Studies. UC San Diego faculty, researchers, and alumni have won twenty Nobel Prizes, eight National Medals of Science, eight MacArthur Fellowships, two Pulitzer Prizes, and two Fields Medals. Additionally, of the current faculty, 29 have been elected to the National Academy of Engineering, 95 to the National Academy of Sciences, and 106 to the American Academy of Arts and Sciences.
University of California, San Diego research articles from Innovation Toronto
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Transparent window coatings that keep buildings and cars cool on sunny days. Devices that could more than triple solar cell efficiencies. Thin, lightweight shields that block thermal detection. These are potential applications for a thin, flexible, light-absorbing material developed by engineers at the University of California San Diego.
The material, called a near-perfect broadband absorber, absorbs more than 87 percent of near-infrared light (1,200 to 2,200 nanometer wavelengths), with 98 percent absorption at 1,550 nanometers, the wavelength for fiber optic communication. The material is capable of absorbing light from every angle. It also can theoretically be customized to absorb certain wavelengths of light while letting others pass through.
Materials that “perfectly” absorb light already exist, but they are bulky and can break when bent. They also cannot be controlled to absorb only a selected range of wavelengths, which is a disadvantage for certain applications. Imagine if a window coating used for cooling not only blocked infrared radiation, but also normal light and radio waves that transmit television and radio programs.
By developing a novel nanoparticle-based design, a team led by professors Zhaowei Liu and Donald Sirbuly at the UC San Diego Jacobs School of Engineering has created a broadband absorber that’s thin, flexible and tunable. The work was published online on Jan. 24 in Proceedings of the National Academy of Sciences.
“This material offers broadband, yet selective absorption that could be tuned to distinct parts of the electromagnetic spectrum,” Liu said.
The absorber relies on optical phenomena known as surface plasmon resonances, which are collective movements of free electrons that occur on the surface of metal nanoparticles upon interaction with certain wavelengths of light. Metal nanoparticles can carry a lot of free electrons, so they exhibit strong surface plasmon resonance — but mainly in visible light, not in the infrared.
UC San Diego engineers reasoned that if they could change the number of free electron carriers, they could tune the material’s surface plasmon resonance to different wavelengths of light. “Make this number lower, and we can push the plasmon resonance to the infrared. Make the number higher, with more electrons, and we can push the plasmon resonance to the ultraviolet region,” Sirbuly said. The problem with this approach is that it is difficult to do in metals.
To address this challenge, engineers designed and built an absorber from materials that could be modified, or doped, to carry a different amount of free electrons: semiconductors. Researchers used a semiconductor called zinc oxide, which has a moderate number of free electrons, and combined it with its metallic version, aluminum-doped zinc oxide, which houses a high number of free electrons — not as much as an actual metal, but enough to give it plasmonic properties in the infrared.
|Schematic of the nanotube array|
The materials were combined and structured in a precise fashion using advanced nanofabrication technologies in the Nano3 cleanroom facility at the Qualcomm Institute at UC San Diego. The materials were deposited one atomic layer at a time on a silicon substrate to create an array of standing nanotubes, each made of alternating concentric rings of zinc oxide and aluminum-doped zinc oxide. The tubes are 1,730 nanometers tall, 650 to 770 nanometers in diameter, and spaced less than a hundred nanometers apart. The nanotube array was then transferred from the silicon substrate to a thin, elastic polymer. The result is a material that is thin, flexible and transparent in the visible.
“There are different parameters that we can alter in this design to tailor the material’s absorption band: the gap size between tubes, the ratio of the materials, the types of materials, and the electron carrier concentration. Our simulations show that this is possible,” said Conor Riley, a recent nanoengineering Ph.D. graduate from UC San Diego and the first author of this work. Riley is currently a postdoctoral researcher in Sirbuly’s group.
|SEM images of a nanotube array: side view (left) and top view (right)|
Those are just a few exciting features of this particle-based design, researchers said. It’s also potentially transferrable to any type of substrate and can be scaled up to make large surface area devices, like broadband absorbers for large windows. “Nanomaterials normally aren’t fabricated at scales larger than a couple centimeters, so this would be a big step in that direction,” Sirbuly said.
Nanomaterials can store all kinds of things, including energy, drugs and other cargo
A team of chemists led by Northwestern University’s William Dichtel has cooked up something big: The scientists created an entirely new type of nanomaterial and watched it form in real time — a chemistry first.
“Our work sets the stage for researchers interested in studying the fundamental properties of interesting materials and applied systems, such as solar cells, batteries, sensors, paints and drug delivery systems,” said Dichtel, the Robert L. Letsinger Professor of Chemistry at the Weinberg College of Arts and Sciences. “The findings have enormous implications for how chemists and materials scientists think about nanotechnology and their science in general.”
The researchers made covalent organic frameworks (COFs) that are stable — a major advancement. These strong, stiff polymers with an abundance of tiny pores are suitable for storing all kinds of things, including energy, drugs and other cargo. But what limits COFs from realizing these applications is that they are usually prepared as powdery substances that can’t be processed into useful forms.
In this study, the nanoparticles stay suspended in a liquid “ink,” creating a new nanomaterial called a COF colloid. This structure allows the unique materials to be processed into useful forms, such as films of arbitrary size and thickness.
Also, for the first time, the chemists demonstrated that the “cooking,” or heating up, of the ingredients for the nanomaterial can take place inside the imaging tool itself, in this case a powerful microscope called a transmission electron microscope. With this new technique, Dichtel and his team could investigate how molecules come together to form COF colloids.
The field of covalent organic frameworks is only a decade old, and much needs to be learned about how the porous polymers form and how to keep them stable. Dichtel is a leader in the young field, focused on bringing unprecedented functionality and improved stability to COFs.
The study, titled “Colloidal Covalent Organic Frameworks,” was published last week in the journal ACS Central Science. Dichtel is a corresponding author of the study.
The COF colloids are nanoparticles (approximately 50 nanometers in diameter, roughly the size of a virus) made from any number of building blocks in a predictable way. The COF colloids also feature small pores, whose size, shape and chemical groups can be designed precisely. (Each pore is approximately 2.5 nanometers wide, big enough to hold a variety of cargo.)
“This is about as close to useful ‘molecular LEGOs’ as I’ve seen,” Dichtel said. “Being able to keep these materials stable in solution is a major step forward towards taking advantage of their unique combination of properties.”
For the study, Dichtel teamed up with Nathan C. Gianneschi at the University of California, San Diego, who has developed cutting-edge analysis techniques. Gianneschi, a professor of chemistry and biochemistry, is also a corresponding author of the paper.
Dichtel and Gianneschi developed a new way to watch COF colloids form inside a transmission electron microscope, another major advancement.
The inability to observe reactions as they occur using electron microscopy has been a major limitation, Gianneschi said. Usually samples have to be dried or frozen to use this technique. The microscopy in this study opens the door to a new dimension: allowing scientists to initiate and observe materials as they form in real time.
“This is something that is routine on the macroscale, of course, but has eluded chemists, biologists and physicists at the nanoscale,” Gianneschi said.
Researchers at the University of California San Diego have demonstrated the world’s first laser based on an unconventional wave physics phenomenon called bound states in the continuum. The technology could revolutionize the development of surface lasers, making them more compact and energy-efficient for communications and computing applications.
The new BIC lasers could also be developed as high-power lasers for industrial and defense applications.
“Lasers are ubiquitous in the present day world, from simple everyday laser pointers to complex laser interferometers used to detect gravitational waves. Our current research will impact many areas of laser applications,” said Ashok Kodigala, an electrical engineering Ph.D. student at UC San Diego and first author of the study.
“Because they are unconventional, BIC lasers offer unique and unprecedented properties that haven’t yet been realized with existing laser technologies,” said Boubacar Kanté, electrical engineering professor at the UC San Diego Jacobs School of Engineering who led the research.
For example, BIC lasers can be readily tuned to emit beams of different wavelengths, a useful feature for medical lasers made to precisely target cancer cells without damaging normal tissue. BIC lasers can also be made to emit beams with specially engineered shapes (spiral, donut or bell curve) — called vector beams — which could enable increasingly powerful computers and optical communication systems that can carry up to 10 times more information than existing ones.
“Light sources are key components of optical data communications technology in cell phones, computers and astronomy, for example. In this work, we present a new kind of light source that is more efficient than what’s available today in terms of power consumption and speed,” said Babak Bahari, an electrical engineering Ph.D. student in Kanté’s lab and a co-author of the study.
Bound states in the continuum (BICs) are phenomena that have been predicted to exist since 1929. BICs are waves that remain perfectly confined, or bound, in an open system. Conventional waves in an open system escape, but BICs defy this norm — they stay localized and do not escape despite having open pathways to do so.
In a previous study, Kanté and his team demonstrated, at microwave frequencies, that BICs could be used to efficiently trap and store light to enable strong light-matter interaction. Now, they’re harnessing BICs to demonstrate new types of lasers. The team published the work Jan. 12 in Nature.
Controls engineers at UC San Diego have developed practical strategies for building and coordinating scores of sensor-laden balloons within hurricanes.
Using onboard GPS and cellphone-grade sensors, each drifting balloon becomes part of a “swarm’’ of robotic vehicles, which can periodically report, via satellite uplink, their position, the local temperature, pressure, humidity and wind velocity.
This new, comparatively low-cost sensing strategy promises to provide much-needed in situ sampling of environmental conditions for a longer range of time and from many vantage points within developing hurricanes. This has the potential to greatly improve efforts to estimate and forecast the intensity and track of future hurricanes in real time.
Current two to five day forecasts of many hurricanes deviate significantly from each other, and from the truth. For example, as Hurricane Matthew churned toward the eastern seaboard in early October of 2016, various news outlets reported “forecasts” like “Hurricane Matthew will probably make landfall somewhere between Charleston and Boston, so everyone brace yourselves.”
“Guidance like this is entirely inadequate for evacuation and emergence response preparations,” said Thomas Bewley, a professor at the Jacobs School of Engineering at UC San Diego and the paper’s senior author.
Improved forecasts, to be greatly facilitated by improved in situ environmental sampling, are essential to protect property and save lives from such extreme environmental threats, he added.
Key challenges in this effort include the design of small, robust, buoyancy-controlled balloons that won’t accumulate ice; the efficient coordination of the motion of these balloons to keep them moving within the hurricane, between an altitude of 0 and 8 kilometers (about 5 miles); and to keep them well distributed over the dynamically significant regions within the hurricane, for up to a week at a time.
Bewley and UC San Diego post-doctoral researcher Gianluca Meneghello detail various aspects of their work on this problem in the October 2016 issue of the Physical Review Fluids, building upon work they published in the proceedings of the eighth International Symposium on Stratified Flows (ISSF) in San Diego, (Sept. 1, 2016). They plan to expand on their work at the forthcoming IEEE Aerospace Conference in Big Sky, Mont. (March 6, 2017).
|Typical spread of the zero- to five-day forecasts of the track of Hurricane Matthew, as performed by the major hurricane forecasting centers on (left) Oct 3, (middle) Oct 6, and (right) Oct 7, 2016.|
Data from http://www.emc.ncep.noaa.gov/gc_wmb/vxt/HWRF/tcall.php?selectYear=2016&selectBasin=North+Atlantic&selectStorm=MATTHEW14L
How the model works
The model for large-scale coordination of balloon swarms within hurricanes, as discussed in the Physical Review Fluids article, uses a clever strategy to model predictive control by leveraging the cutting-edge Weather Research and Forecasting code developed by the National Center for Atmospheric Research, the National Oceanic and Atmospheric Administration and the Air Force Weather Agency (AFWA). Multiple simulations indicate the remarkable effectiveness of this approach, including a simulation based on the evolution of Hurricane Katrina as it moved across the Gulf of Mexico, as summarized in the video available at http://flowcontrol.ucsd.edu/katrina.mp4
`The key idea of our large-scale balloon coordination strategy,’’ said Bewley, “is to `go with the flow,’ commanding small vertical movements of the balloons and leveraging the strong vertical stratification of the horizontal winds within the hurricane to distribute the balloons in the desired fashion horizontally.”
Intermediate-scale and small-scale fluctuations in the violent turbulent flow of a hurricane, which are unresolved by forecasting codes like WRF, are quite substantial. The researchers’ strategy? “We simply ride out the smaller-scale fluctuations of the flow,” said Meneghello. “The smaller-scale flowfield fluctuations induce something of a random walk in the balloon motion. We model these fluctuations statistically, and respond with corrections only if a balloon deviates too far from its desired location in the formation.”
Background on the project
As summarized in their ISSF paper, the researchers’ strategy for applying such corrections, dubbed Three Level Control (and endearingly abbreviated TLC), applies a finite shift to the vertical location of the displaced balloon for a short period of time, again leveraging the strong vertical stratification of the horizontal winds to return the balloon to its nominal desired location.
A third essential ingredient of the project, summarized in the researchers’ IEEE paper, is the design of small (about 3 kg or 6.5 lbs.), robust, energetically-efficient, buoyancy-controlled balloons that can survive, without significant accumulation of ice, in the cold, wet, turbulent, electrically active environment of a hurricane. The balloons can operate effectively for up to a week at a time on a battery charge not much larger than that of a handful of iPhones. “Cellphone-grade technologies, for both environmental sensors as well as low-energy radios and microprocessors, coupled with new space-grade balloon technology developed by Thin Red Line Aerospace, are on the cusp of making this ambitious robotic sensing mission feasible,” said Bewley.
Control theory applied
In addition to robotics, Bewley’s team specializes in the field of control theory, which is the essential “hidden technology” in many engineering applications, such as cruise control and adaptive suspension systems in cars, stability augmentation systems in high-performance aircraft and adaptive noise cancellation in telecommunication. Control theory made it possible for SpaceX rockets to land on barges at sea.
Though the math and numerical methods involved are sophisticated, the fundamental principle is straightforward: sensors take measurements of the physical environment, then a computer uses these measurements in real time to coordinate appropriate responses by the system (in this case, the buoyancy of the balloons) to achieve the desired effect.
Bewley, Meneghello and colleagues are now working towards testing the balloons and algorithms designed in this study in the real world. With sensor balloon swarms and the special TLC coming out of their lab, fire and safety officials may soon have a crucial extra couple of days to move people out of harm’s way, and to prepare emergency responses, when the next Katrina or Sandy threatens.
Biologists have discovered that the evolution of a new species can occur rapidly enough for them to observe the process in a simple laboratory flask.
In a month-long experiment using a virus harmless to humans, biologists working at the University of California San Diego and at Michigan State University documented the evolution of a virus into two incipient species—a process known as speciation that Charles Darwin proposed to explain the branching in the tree of life, where one species splits into two distinct species during evolution.
“Many theories have been proposed to explain speciation, and they have been tested through analyzing the characteristics of fossils, genomes, and natural populations of plants and animals,” said Justin Meyer, an assistant professor of biology at UC San Diego and the first author of a study that will be published in the December 9 issue of Science.“However, speciation has been notoriously difficult to thoroughly investigate because it happens too slowly to directly observe. Without direct evidence for speciation, some people have doubted the importance of evolution and Darwin’s theory of natural selection.”
Meyer’s study, which also appeared last week in an early online edition of Science, began while he was a doctoral student at Michigan State University, working in the laboratory of Richard Lenski, a professor of microbial ecology there who pioneered the use of microorganisms to study the dynamics of long-term evolution.
“Even though we set out to study speciation in the lab, I was surprised it happened so fast,” said Lenski, a co-author of the study. “Yet the deeper Justin dug into things—from how the viruses infected different hosts to their DNA sequences—the stronger the evidence became that we really were seeing the early stages of speciation.”
“With these experiments, no one can doubt whether speciation occurs,” Meyer added. “More importantly, we now have an experimental system to test many previously untestable ideas about the process.”
To conduct their experiment, Meyer, Lenski and their colleagues cultured a virus—known as “bacteriophage lambda”—capable of infecting E. coli bacteria using two receptors, molecules on the outside of the cell wall that viruses use to attach themselves and then infect cells.
When the biologists supplied the virus with two types of cells that varied in their receptors, the virus evolved into two new species, one specialized on each receptor type.
“The virus we started the experiment with, the one with the nondiscriminatory appetite, went extinct. During the process of speciation, it was replaced by its more evolved descendants with a more refined palette,” explained Meyer.
Why did the new viruses take over?
“The answer is as simple as the old expression, ‘a jack of all trades is a master of none’,” explained Meyer. “The specialized viruses were much better at infecting through their preferred receptor and blocked their ‘jack of all trades’ ancestor from infecting cells and reproducing. The survival of the fittest led to the emergence of two new specialized viruses.”
Researchers from the University of California San Diego have developed a novel design for a compact, ultra-sensitive nanosensor that can be used to make portable health-monitoring devices and to detect minute quantities of toxins and explosives for security applications.
The study addresses one of the major challenges of nanosensor design: how to increase sensitivity while reducing size.
The nanosensor design presented in this study combines three-dimensional plasmonic nanoparticles with singularities called exceptional points—a combination that’s being demonstrated for the first time. “The new physics implemented here could potentially outcompete the plasmonic technologies currently in use for sensing,” said Boubacar Kanté, electrical engineering professor at the UC San Diego Jacobs School of Engineering and senior author of the study. Kanté and his team published their novel design Nov. 8 online in the rapid communication section of the journal Physical Review B.
Singularities, such as exceptional points, are fundamental in physics due to their uncanny ability to induce a large response from a small excitation, Kanté explained. Singularities occur when a quantity is undefined or infinite, such as the density at the center of black hole, for example. Exceptional points occur when two waves become degenerate, meaning that both their resonant frequencies and spatial structure merge as one.
“Exceptional points have been highly sought after for sensors and enhanced light-matter interactions,” said Ashok Kodigala, a PhD student in Kanté’s lab and first author of the study. “The possibility to demonstrate exceptional points in systems that are simultaneously sub-wavelength and compatible with small biological molecules for sensing has remained elusive—until now.”
Nanosensors operate based on a phenomenon called frequency splitting, meaning that the presence of a substance perturbs the degeneracy between two resonant frequencies and causes a detectable split. In an exceptional-point-based nanosensor, resonant frequencies would split much faster than they do in traditional nanosensors, giving rise to enhanced detection capabilities.
By combining exceptional points and plasmonics, researchers formulated a design for a nanosensor that is both compact and ultra-sensitive.
“We believed that designing such a nanosensor requires not just a gradual improvement of existing devices, but a conceptual breakthrough. That is why we chose to focus on exceptional-point-based-nanosensors,” Kodigala said.
In this study, researchers proposed what Kodigala calls “a general recipe to obtain exceptional points on demand.” The method involves controlling the interaction between symmetry-compatible modes of the plasmonic system.
The nanosensor design has only been demonstrated computationally so far. The team is working on integrating the exceptional-point-based nanosensors on a chip.
“Once we optimize some of the main parameters of this system to minimize ohmic and radiative losses, we can start transitioning this research from the theoretical stage to a commercially relevant product,” Kanté said. The team has filed a patent on the technology.
A team of mechanical engineers at the University of California San Diego has successfully used acoustic waves to move fluids through small channels at the nanoscale. The breakthrough is a first step toward the manufacturing of small, portable devices that could be used for drug discovery and microrobotics applications. The devices could be integrated in a lab on a chip to sort cells, move liquids, manipulate particles and sense other biological components. For example, it could be used to filter a wide range of particles, such as bacteria, to conduct rapid diagnosis.
The researchers detail their findings in the Nov. 14 issue of Advanced Functional Materials. This is the first time that surface acoustic waves have been used at the nanoscale.
The field of nanofluidics has long struggled with moving fluids within channels that are 1000 times smaller than the width of a hair, said James Friend, a professor and materials science expert at the Jacobs School of Engineering at UC San Diego. Current methods require bulky and expensive equipment as well as high temperatures. Moving fluid out of a channel that’s just a few nanometers high requires pressures of 1 megaPascal, or the equivalent of 10 atmospheres.
Researchers led by Friend had tried to use acoustic waves to move the fluids along at the nano scale for several years. They also wanted to do this with a device that could be manufactured at room temperature.
After a year of experimenting, post-doctoral researcher Morteza Miansari, now at Stanford, was able to build a device made of lithium niobate with nanoscale channels where fluids can be moved by surface acoustic waves. This was made possible by a new method Miansari developed to bond the material to itself at room temperature. The fabrication method can be easily scaled up, which would lower manufacturing costs. Building one device would cost $1000 but building 100,000 would drive the price down to $1 each.
The device is compatible with biological materials, cells and molecules.
Researchers used acoustic waves with a frequency of 20 megaHertz to manipulate fluids, droplets and particles in nanoslits that are 50 to 250 nanometers tall. To fill the channels, researchers applied the acoustic waves in the same direction as the fluid moving into the channels. To drain the channels, the sound waves were applied in the opposite direction.
By changing the height of the channels, the device could be used to filter a wide range of particles, down to large biomolecules such as siRNA, which would not fit in the slits. Essentially, the acoustic waves would drive fluids containing the particles into these channels. But while the fluid would go through, the particles would be left behind and form a dry mass. This could be used for rapid diagnosis in the field.
A team of engineers at the University of California San Diego has developed a magnetic ink that can be used to make self-healing batteries, electrochemical sensors and wearable, textile-based electrical circuits.
The key ingredient for the ink is microparticles oriented in a certain configuration by a magnetic field. Because of the way they’re oriented, particles on both sides of a tear are magnetically attracted to one another, causing a device printed with the ink to heal itself. The devices repair tears as wide as 3 millimeters—a record in the field of self-healing systems.
Researchers detail their findings in the Nov. 2 issue of Science Advances.
“Our work holds considerable promise for widespread practical applications for long-lasting printed electronic devices,” said Joseph Wang, director of the Center for Wearable Sensors and chair of the nanoengineering department at UC San Diego.
Existing self-healing materials require an external trigger to kick start the healing process. They also take anywhere between a few minutes to several days to work. By contrast, the system developed by Wang and colleagues doesn’t require any outside catalyst to work. Damage is repaired within about 50 milliseconds (0.05 seconds).
Engineers used the ink to print batteries, electrochemical sensors and wearable, textile-based electrical circuits (see video). They then set about damaging these devices by cutting them and pulling them apart to create increasingly wide gaps. Researchers repeatedly damaged the devices nine times at the same location. They also inflicted damage in four different places on the same device. The devices still healed themselves and recovered their function while losing a minimum amount of conductivity.
For example, nanoengineers printed a self-healing circuit on the sleeve of a T-shirt and connected it with an LED light and a coin battery. The researchers then cut the circuit and the fabric it was printed on. At that point, the LED turned off. But then within a few seconds it started turning back on as the two sides of the circuit came together again and healed themselves, restoring conductivity.
“We wanted to develop a smart system with impressive self-healing abilities with easy-to-find, inexpensive materials,” said Amay Bandodkar, one of the papers’ first authors, who earned his Ph.D. in Wang’s lab and is now a postdoctoral researcher at Northwestern University.
Wang’s research group is a leader in the field of printed wearable sensors, so his team of nanoengineers naturally turned to ink as a starting point for their self-healing system.
Engineers loaded the ink with microparticles made of a type of magnet commonly used in research and made of neodymium, a soft, silvery metal. The particles’ magnetic field is much larger than their individual size. This is the key to the ink’s self-healing properties because the attraction between the particles leads to closing tears that are millimeters wide.
The particles also conduct electricity and are inexpensive. But they have poor electrochemical properties, making them difficult to use in the electrochemical devices, such as sensors, on their own. To remedy this problem, researchers added carbon black to the ink, a material commonly used to make batteries and sensors.
But researchers realized that the microparticles’ magnetic fields, when in their natural configuration, canceled each other out, which robbed them of their healing properties. Engineers solved this by printing the ink in the presence of an external magnetic field, which ensured that the particles oriented themselves to behave as a permanent magnet with two opposite poles at the end of each printed device. When the device is cut in two, the two damaged pieces act as different magnets that attract each other and self-heal.
In the future, engineers envision making different inks with different ingredients for a wide range of applications. In addition, they plan to develop computer simulations to test different self-healing ink recipes in silico before trying them out in the lab.