New biocompatible electronic devices, encapsulated in silk, can dissolve harmlessly into their surroundings

Smooth as silk 'transient electronics' dissolve in body or environment. Tiny resorbable semiconductors could be used for medical implants, environmental sensors, consumer electronics.

MEDFORD/SOMERVILLE, Mass.(Sept. 27, 2012) --Tiny, fully biocompatible electronic devices that are able to dissolve harmlessly into their surroundings after functioning for a precise amount of time have been created by a research team led by biomedical engineers at Tufts University in collaboration with researchers at the University of Illinois at Urbana-Champaign.

Dubbed "transient electronics," the new class of silk-silicon devices promises a generation of medical implants that never need surgical removal, as well as environmental monitors and consumer electronics that can become compost rather than trash.

"These devices are the polar opposite of conventional electronics whose integrated circuits are designed for long-term physical and electronic stability," says Fiorenzo Omenetto, professor of biomedical engineering at Tufts School of Engineering and a senior and corresponding author on the paper "A Physically Transient Form of Silicon Electronics" published in the September 28, 2012, issue of Science.

Caption: New biocompatible electronic devices, encapsulated in silk, can dissolve harmlessly into their surroundings after a precise amount of time. These "transient electronics" promise medical implants that never need surgical removal, as well as environmental monitors and consumer electronics that can become compost rather than trash. Here, a biodegradable integrated circuit -- including transistors, diodes, inductors and capacitors-- is partially dissolved by a droplet of water. The image is courtesy of Tufts University and the University of Illinois. Credit: Photo credit: Fiorenzo Omenetto/Tufts University Usage Restrictions: Use with proper captioning and credit

"Transient electronics offer robust performance comparable to current devices but they will fully resorb into their environment at a prescribed time—ranging from minutes to years, depending on the application," Omenetto explains. "Imagine the environmental benefits if cell phones, for example, could just dissolve instead of languishing in landfills for years." The futuristic devices incorporate the stuff of conventional integrated circuits -- silicon and magnesium -- but in an ultrathin form that is then encapsulated in silk protein. "While silicon may appear to be impermeable, eventually it dissolves in water," says Omenetto. The challenge, he notes, is to make the electrical components dissolve in minutes rather than eons. Researchers led by UIUC's John Rogers -- the other senior and corresponding author -- are pioneers in the engineering of ultrathin flexible electronic components. Only a few tens of nanometers thick, these tiny circuits, from transistors to interconnects, readily dissolve in a small amount of water, or body fluid, and are harmlessly resorbed. Controlling materials at these scales makes it possible to fine-tune how long it takes the devices to dissolve. Device dissolution is further controlled by sheets of silk protein in which the electronics are supported and encapsulated. Extracted from silkworm cocoons, silk protein is one of the strongest, most robust materials known. It's also fully biodegradable and biofriendly and is already used for some medical applications. Omenetto and his Tufts colleagues have discovered how to adjust the properties of silk so that it degrades at a wide range of intervals. The researchers successfully demonstrated the new platform by testing a thermal device designed to monitor and prevent post-surgical infection (demonstrated in a rat model) and also created a 64 pixel digital camera.

Collaborating with Omenetto from Tufts' Department of Biomedical Engineering were Hu Tao, research assistant professor and co-first author on the paper; Mark A. Brenckle, doctoral student; Bruce Panilaitis, program administrator; Miaomiao Yang, doctoral student; and David L. Kaplan, Stern Family Professor of Engineering and department chair. In addition to Tufts and UIUC, co-authors on the paper also came from Seoul National University, Northwestern University, Dalian University of Technology (China), Nano Terra (Boston), and the University of Arizona.

In the future, the researchers envision more complex devices that could be adjustable in real time or responsive to changes in their environment, such as chemistry, light or pressure.

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The work was supported by the Defense Advanced Research Projects Agency, the National Science Foundation, the Air Force Office of Scientific Research Multi University Research Initiative program, the National Institute of Biomedical Imaging and Bioengineering of the National Institutes of Health under award EB002520 and the U.S. Department of Energy.

Tufts University School of Engineering Located on Tufts' Medford/Somerville campus, the School of Engineering offers a rigorous engineering education in a unique environment that blends the intellectual and technological resources of a world-class research university with the strengths of a top-ranked liberal arts college.

Close partnerships with Tufts' excellent undergraduate, graduate and professional schools, coupled with a long tradition of collaboration, provide a strong platform for interdisciplinary education and scholarship. The School of Engineering's mission is to educate engineers committed to the innovative and ethical application of science and technology in addressing the most pressing societal needs, to develop and nurture twenty-first century leadership qualities in its students, faculty, and alumni, and to create and disseminate transformational new knowledge and technologies that further the well-being and sustainability of society in such cross-cutting areas as human health, environmental sustainability, alternative energy, and the human-technology interface.

Contact: Kim Thurler kim.thurler@tufts.edu 617-627-3175 Tufts University

Hairy nanoparticles can cheaply and conveniently measure mercury, which attacks the nervous system

ANN ARBOR, Mich.—A strip of glass covered in hairy nanoparticles can cheaply and conveniently measure mercury, which attacks the nervous system, and other toxic metals in fluids.

Researchers at the Swiss Federal Institute of Technology (EPFL), Northwestern University and the University of Michigan found that their new method can measure methyl mercury, the most common form of mercury pollution, at unprecedentedly small concentrations. The system, which could test for metal toxins in drinking water and fish, is reported in the current edition of Nature Materials.

Methyl mercury dumped in lakes and rivers accumulates in fish, reaching its highest levels in large, predatory fish such as tuna and swordfish. Young children and pregnant women are advised to avoid eating these fish because mercury can affect the developing brain and nervous system. While metals in drinking water are measured periodically, these measurements say little about migratory fish, including tuna, which may pass through more polluted areas.

Coal plants like this one in West Chicago release mercury into the atmosphere which can end up in the water supply. This plant, the Crawford Generating Station, is among the last coal-fired plants to shut down in the city, and this move could help bring the already low mercury content in nearby Lake Michigan down even further. Image credit: Steve Geer, Chicago Image Gate

"The problem is that current monitoring techniques are too expensive and complex," said researcher Francesco Stellacci, the Constellium Chair holder at EPFL. "With a conventional method, you have to send samples to the laboratory, and the analysis equipment costs several million dollars." Using the device invented by the Swiss-American team, measuring the mercury levels in water or dissolved fish meat is as simple as dipping a strip of coated glass into the fluid. Metals and metallic molecules, such as methyl mercury, typically become positively charged ions in water. When these ions drift between the hairy nanoparticles, the hairs close up, trapping the pollutant. Passing a current over the strip of glass reveals how many ions are caught in the "nano-velcro." Each ion allows the strip to conduct more electricity. U-M researchers Hao Jiang and Sharon Glotzer, the Churchill Professor of Chemical Engineering, performed computer simulations that investigated how the nano-velcro traps pollutants.

They showed that the hairy nanoparticles are choosey about which ions they capture, confirming that the strips can give reliable measures of specific toxins as demonstrated by the experimental findings of the Swiss group.

"By making detection of pollutants and toxins cheap and easy to do, more testing at the source will lead to safer foods on the dinner table and in kids' lunchboxes," Glotzer said.

The scientists targeted particular pollutants by varying the length of the nano-hairs. This approach is especially successful for methyl mercury, and the device can measure it with record-breaking accuracy, detecting concentrations as low as 600 methyl mercury ions per cubic centimeter of water. Fortunately, that level of precision won't break the bank. The researchers estimate that the coated glass strips could cost less than 10 dollars each, while the measurement device will cost only a few hundred dollars. It could gauge the concentration of metals onsite and within minutes.

The researchers tested their method in Lake Michigan, near Chicago.

"The goal was to compare our measurements to FDA measurements done using conventional methods," Stellacci said.

Despite the industrial activity in the region, mercury levels were extremely low, in agreement with the FDA's analysis. The team also tested a mosquito fish from the Everglades.

"We measured tissue that had been dissolved in acid. The goal was to see if we could detect even very minuscule quantities," said Bartosz Grzybowski, the K. Burgess Professor of Physical Chemistry and Chemical Systems Engineering at Northwestern University, noting the species is too low on the food chain to accumulate high levels of mercury.

The United States Geological Survey reported near-identical results after analyzing the same sample.

"With this technology, it will be possible to conduct tests on a much larger scale in the field, or even in fish before they are put on the market," said researcher Hyewon Kim, MIT student visiting EPFL.

Funding for this research came from ENI, via the ENI-MIT Alliance; the U.S. Defense Threat Reduction Agency via a grant to MIT and U-M; and the U.S. Department of Energy via a Nonequilibrium Energy Research Center grant to Northwestern and the U-M.

Contact: Nicole Casal Moore ncmoore@umich.edu 734-647-7087 University of Michigan

Resonant nanoelectromechanical systems (NEMS) have the potential to have significant impact in mass sensing, signal processing and field detection applications

Resonant nanoelectromechanical systems (NEMS) have the potential to have significant impact in mass sensing, signal processing and field detection applications if the challenges associated with processing, material and geometric variability can be mitigated.

WEST LAFAYETTE, Ind. - Researchers have learned how to mass produce tiny mechanical devices that could help cell phone users avoid the nuisance of dropped calls and slow downloads. The devices are designed to ease congestion over the airwaves to improve the performance of cell phones and other portable devices.

"There is not enough radio spectrum to account for everybody's handheld portable device," said Jeffrey Rhoads, an associate professor of mechanical engineering at Purdue University.

The overcrowding results in dropped calls, busy signals, degraded call quality and slower downloads. To counter the problem, industry is trying to build systems that operate with more sharply defined channels so that more of them can fit within the available bandwidth.

This image from a scanning electron microscope shows a tiny mechanical device, an electrostatically actuated nanoresonator, that might ease congestion over the airwaves to improve the performance of cell phones and other portable devices. (Purdue University image)

"To do that you need more precise filters for cell phones and other radio devices, systems that reject noise and allow signals only near a given frequency to pass," said Saeed Mohammadi, an associate professor of electrical and computer engineering who is working with Rhoads, doctoral student Hossein Pajouhi and other researchers. The Purdue team has created devices called nanoelectromechanical resonators, which contain a tiny beam of silicon that vibrates when voltage is applied. Researchers have shown that the new devices are produced with a nearly 100 percent yield, meaning nearly all of the devices created on silicon wafers were found to function properly. "We are not inventing a new technology, we are making them using a process that's amenable to large-scale fabrication, which overcomes one of the biggest obstacles to the widespread commercial use of these devices," Rhoads said. Findings are detailed in a research paper appearing online in the journal IEEE Transactions on Nanotechnology. The paper was written by doctoral students Lin Yu and Pajouhi, Rhoads, Mohammadi, and graduate student Molly Nelis.

In addition to their use as future cell phone filters, such nanoresonators also could be used for advanced chemical and biological sensors in medical and homeland-defense applications and possibly as components in computers and electronics.

The devices are created using silicon-on-insulator, or SOI, fabrication - the same method used by industry to manufacture other electronic devices. The resonators can be readily integrated into electronic circuits and systems because SOI is compatible with complementary metal–oxide–semiconductor technology, or CMOS, another mainstay of electronics manufacturing used to manufacture computer chips.

The resonators are in a class of devices called nanoelectromechanical systems, or NEMS.

The new device is said to be "highly tunable," which means it could enable researchers to overcome manufacturing inconsistencies that are common in nanoscale devices.

"Because of manufacturing differences, no two nanoscale devices perform the same rolling off of the assembly line," Rhoads said. "You must be able to tune them after processing, which we can do with these devices."

The heart of the device is a silicon beam attached at two ends. The beam, which vibrates in the center like a jump rope, is about two microns long and 130 nanometers wide, or about 1,000 times thinner than a human hair. Applying alternating current to the beam causes it to selectively vibrate side-to-side or up and down and also allows the beam to be finely adjusted, or tuned.

The nanoresonators were shown to control their vibration frequencies better than other resonators. The devices might replace electronic parts to achieve higher performance and lower power consumption.

"A vivid example is a tunable filter," Mohammadi said. "It is very difficult to make a good tunable filter with transistors, inductors and other electronic components, but a simple nanomechanical resonator can do the job with much better performance and at a fraction of the power."

Not only are they more efficient than their electronic counterparts, he said, but they also are more compact.

"Because the devices are tiny and the fabrication has almost a 100 percent yield, we can pack millions of these devices in a small chip if we need to," Mohammadi said. "It's too early to know exactly how these will find application in computing, but since we can make these tiny mechanical devices as easily as transistors, we should be able to mix and match them with each other and also with transistors in order to achieve specific functions. Not only can you put them side-by-side with standard computer and electronic chips, but they tend to work with near 100 percent reliability."

The new resonators could provide higher performance than previous MEMS, or microelectromechanical systems.

In sensing application, the design enables researchers to precisely measure the frequency of the vibrating beam, which changes when a particle lands on it. Analyzing this frequency change allows researchers to measure minute masses. Similar sensors are now used to research fundamental scientific questions. However, recent advances may allow for reliable sensing with portable devices, opening up a range of potential applications, Rhoads said.

Such sensors have promise in detecting and measuring constituents such as certain proteins or DNA for biological testing in liquids, gases and the air, and the NEMS might find applications in breath analyzers, industrial and food processing, national security and defense, and food and water quality monitoring.

"The smaller your system, the smaller the mass you can measure," Rhoads said. "Most of the field-deployable sensors we've seen in the past have been based on microscale technologies, so this would be hundreds or thousands of times smaller, meaning we should eventually be able to measure things that much smaller."

The work is based at the Dynamic Analysis of Micro- and Nanosystems Laboratory at the Birck Nanotechnology Center in Purdue's Discovery Park. Other faculty members and graduate students also use the specialized facility.

The researchers have filed a patent application for the concept. The research is funded by the National Science Foundation.

Writer: Emil Venere, 765-494-4709, venere@purdue.edu

Sources: Jeffrey Rhoads, 765-494-5630, jfrhoads@purdue.edu

Saeed Mohammadi, 765-494-3557, saeedm@purdue.edu

Note to Journalists: An electronic copy of the research paper is available from Emil Venere, 765-494-4709, venere@purdue.edu