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Vanishing Electronics

By Samuel Greengard

Communications of the ACM, Vol. 56 No. 5, Pages 20-22

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Since the dawn of the digital age, engineers and designers have struggled to make electronics more dependable. They have constructed microchips, circuit boards, and processors to better withstand the forces of natureincluding dust, oxidation, and exposure to various other gasses and substances in the atmosphere. They have also experimented with materials that conduct electricity more effectively and fail less regularly.

Yet times, and electronics, change. Peer into the engineering lab at the University of Illinois Urbana-Champaign and you will view a new generation of electronic devices that will fundamentally change medicine, environmental science, and perhaps spying and warfare. John Rogers, a professor of material science and engineering, is constructing programmable devices that are designed to disintegrate over a period of weeks or months.

Within a few years, so-called transient electronic devices could deliver medication in a highly targeted way, monitor chemical and oil spills, and engage in clandestine tracking and listening for the military. "The disappearance of the device can occur at a physical level through dissolution or sublimation or it can take place at a chemical level as a result of a reaction event that's built into the system," Rogers says. "Transient electronics deliver a completely different design model that can be used in entirely different ways."

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Instability Matters

The origins of today's electronic systems date back to the 1930s. That is when Austrian engineer Paul Eisler developed the first printed circuit boards. These systemswhich allowed engineers to mass-produce circuits with electrical interconnects between specific componentswere initially deployed by the military and used with proximity fuses that would detonate a bomb when it reached a specified distance from a target. By the 1950s, circuit boards and other increasingly sophisticated electronic systems began to appear in televisions, radios, telephones, and various industrial machines.

Today, virtually every electronic devicefrom computer mice to microwave ovens and ceiling fansincorporates integrated circuits, microchips, and other components. These machines can perform in far more complex ways and deliver much higher reliability thanks to these electronic brains. As a result, integrated circuitstypically constructed from silicon, laminates, metals, and resinshave become the building blocks for the digital age. They allow engineers to build an array of devices with computer-like capabilities.

Now, researchers and engineers are turning the concept upside down; they are reexamining the fundamental idea of building electronic systems designed for the long haul. "There is an expectation that if you buy a cellular phone it will last two or three years and if you buy a television it will work for at least 10 years," states Yonggang Huang, a professor of mechanical engineering at Northwestern University in Chicago, Illinois. "The goal with transient electronics is to build a system with planned obsolescence."

Consequently, researchers are now eyeing new materials, manufacturing schemes, device components, and theoretical design tools that support transient electronic systems. This includes ultrathin sheets of silicon and materials like silk, along with transient transistors, diodes, wireless power coils, temperature and strain sensors, photodetectors, solar cells, radio oscillators, antennas, and simple digital cameras that work inside tiny programmable and biocompatible devices. Rogers says these devicesmanufactured from dissolvable magnesium and magnesium oxide (the latter substance is available as a vitamin tablet)could eventually be the size of a grain of sand but possess the same attributes of a conventional microprocessor or the brains of an RFID tag. They would use inductive and radio frequency (RF) wireless technologies with dissolvable single-use batteries to transmit electrical signals.

Depending on the specific design and the way the device is encapsulated into silk, it could react to various chemicals, compounds, temperature, or pH in order to dissolve within minutes or last days, weeks, or potentially years. "The technology is the exact opposite of conventional electronics systems, including integrated circuits, that are designed for long-term physical and electronic stability," explains Fiorenzo Omenetto, professor of biomedical engineering at Tufts University School of Engineering in Medford, MA. "These devices offer robust performance using a bare minimum of electronics. They are able to dissolve or be reabsorbed within a specific timeline." Researchers are also exploring the use of bio-plastics and other fully degradable materials, he notes.

"These devices offer robust performance using a bare minimum of electronics. They are able to dissolve or be reabsorbed within a specific timeline."

In fact, actual transient electronics devices are beginning to take shape. So far, Rogers, Huang, and Omenetto have teamed up to develop several functioning systems. One of them is a basic thermal device designed to monitor and prevent post-surgical infection. The unit, which measures only a few tens of nanometers in thickness and includes a 64-pixel digital camera, has been successfully tested on rats. The silk-based deviceconstructed from tiny circuits, including transistors and interconnectsdissolves in the body and is absorbed into tissue a couple of weeks after being exposed to internal fluids.

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Power Plays

The uses for transient electronics are broadand new possibilities will emerge as the technology takes hold. For example, these devices could usher in a new era of medical monitorsincluding devices that better measure specific heart or kidney performance, for example, and report back to doctors. They could also offer interventional components or therapeutic devices that dispense optimal levels of medication to a specific location within the body. An implantable biocompatible device could be used to administer chemotherapy drugs or treat chronic pain.

In fact, this highly targeted approach to treatment could alleviate the side effects that frequently occur with conventional drugs, especially chemotherapy drugs that affect healthy tissue. Because these devices would monitor or micro-monitor specific areas of the body, they could adjust doses in real-time while providing a stream of data for doctors and other health professionals. In the end, physicians could address problems more promptly and understand how specific medications impact a condition.

But the possibilities for transient electronics do not stop there. Researchers are also developing environmental monitors that could be dropped at the site of chemical or oil spill or into the atmosphere in order to create an instant monitoring network. Scientists could monitor water or air dispersal patterns in order to obtain a more accurate assessment of how different approaches and tools combat the problem. These sensors would dissolve or compost when exposed to water, soil, or air. "They fall into the category of "eco-resorbable," Huang says. "This eliminates the need for collection and recovery or any associated environmental issues."

Finally, transient electronics could be used by the military for monitoring and spying. The U.S. Defense Advanced Research Projects Agency (DARPA), which currently funds research in this field, is exploring ways to use devices that would record video and audio but then disappear, so that there is no record of their existence. Likewise, transient electronics could allow the military or spies to dispense a toxin or medication without being detected. Says Rogers: "The ability to create devices that can disappear without a trace could redefine military and security applications."

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Switching on the future

Although researchers are in the early stages of developing functional transient electronic devices, Rogers believes there is a little doubt they will play a major role in defining the future of medicine and other fields. What's more, as technology continues to advance and the ability to program smaller and smaller devices takes hold, the possibilities are likely to extend to new and different fields. For now, researchers are exploring the use of different materials. For instance, devices constructed with magnesium might also assist with the intake of minerals and vitamins that are essential for a healthy body.

One thing is certain: over the next decade, the field will continue to advance and transient electronics will unlock new opportunities and possibilities.

Eventually, Rogers believes that transient electronics could replace conventional microprocessor and electronics designs. "At a certain point, you have to ask whether we might be able to build computers and cellphones with a specific lifespan and an ability to disintegrate into the environment. The ability to reduce overall waste and mitigate the hazardous waste stream could fundamentally change the way we build, consume, and discard an array of devices," he explains.

Omenetto says that in addition to examining different combinations of transient materials, researchers are studying how they can assemble and combine all the different elements optimally. A key is executing software code in a way that provides the maximum possible results. "There is a huge focus on reliability and issues such as mean-time to failure. Obviously, if the device is used for medical purposes there are issues relating to approval by the Federal Drug Administration (FDA) and its counterparts in other countries."

One thing is certain: over the next decade, the field will continue to advance and transient electronics will unlock new opportunities and possibilities. Although research is still in the early stages, it will gain momentum as multidisciplinary teams build rapidly on learning, Rogers says. "The actual electronics required for these systems is relatively modest. The challenges largely revolve around building systems that optimize the technology and are conducive to large-scale mass-production at a relatively low cost."

In fact, Rogers expects to see an array of actual devices within a few years. "The technology is advancing rapidly. This is an area that offers incredible opportunities in both the medical arena and elsewhere," he concludes. The ability to build transient electronic devices could fundamentally change medicine, environment sciences and other fields. "It represents a fundamentally different approach to building electronic systems. It is an important part of the future of medicine, environmental sciences and other fields."

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Further Reading

Hwang, S., Tao, H., Kim, D., Cheng, H., Song, J., Rill, E., Brenckle, M., Panilaitis, B., Won, S., Kim, Y., Song, Y., Yu, K., Ameen, A., Li, R., Su, Y., Yang, M., Kaplan D.L., Zakin, M.R., Slepian, M.J., Huang, Y, Omenetto, F.G., Rogers, J.A.
A Physically Transient Form of Silicon Electronics, Science 28, September 2012, Vol. 337 no. 6102 pp. 16401644 DOI:10.1126/science.1226325 http://www.sciencemag.org/content/337/6102/1640. abstract

Kim, D., Viventi, J., Amsden, J.J., Xiao, J., Vigeland, L., Kim, Y., Blanco, J.A., Panilaitis, B., Frechette, E.S., Contreras, D., Kaplan, D.L., Omenetto, F.G., Huang, Y., Hwang, K., Zakin, M.R., Litt, B., Rogers, J.A.
Dissolvable Films of Silk Fibroin for Ultrathin Conformal Bio-integrated Electronics, Nature Materials 9, 511517 (2010) doi:10.1038/nmat2745, April 2010. http://www.nature.com/nmat/journal/v9/n6/full/nmat2745.html

Sridharamurthy, S.S., Agarwal, A.K., Beebe, D.J., Jiang, H.
Dissolvable membranes as sensing elements for microfluidics based biological/chemical sensors. Lab on a Chip, Issue 7, 2006. P. 840842.

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Samuel Greengard is an author and journalist based in West Linn, OR.

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UF1Figure. A water droplet dissolves electronic components of a transient electronic device: transistors, diodes, inductors, capacitors and resistors, all on a thin silk substrate.

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