Smooth as Silk

A biodegradable integrated circuit partially dissolved by a droplet of water. This demonstration system includes transistors, diodes, inductors, and capacitors, composed of magnesium electrodes/interconnects, magnesium oxide gate/interlayer dielectrics, and silicon nano-membrane semiconductors, all on a thin film of silk.

A research team – led by biomedical engineers at Tufts University in collaboration with researchers at the University of Illinois at Urbana-Champaign (UIUC) – created tiny, fully biocompatible electronic devices that dissolve harmlessly into their surrounding after functioning for a precise amount of time.

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, Tufts School of Engineering, and a senior and corresponding author on the paper, “A Physically Transient Form of Silicon Electronics.”

“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 ultra-thin form that is then encapsulated in silk protein.

“While silicon may appear to be impermeable, eventually it dissolves in water,” Omenetto says. 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 tenths of a nanometer thick, these tiny circuits, from transistors to interconnects, readily dissolve in a small amount of water, or body fluid, and are harmlessly resorbed, or assimilated. Controlling materials at these scales makes it possible to fine-tune how long it takes the devices to dissolve.

Sheets of silk protein, in which the electronics are supported and encapsulated, further control device dissolution. Extracted from silkworm cocoons, silk protein is one of the strongest, most robust materials known. It is also fully biodegradable and bio-friendly 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 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, researchers envision devices that are more complex, such as ones that are adjustable in real time or responsive to changes in the environment – adapting to chemistry, light, or pressure.

A video of the device in action is available at http://bit.ly/P6BMlg.

Tufts University
Medford, MA
www.tufts.edu

University of Illinois at Urbana-Champaign (UIUC)
Champaign, IL
www.illinois.edu

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