MEDFORD / SOMERVILLE, Mass. (Aug.21, 2019) – A team of engineers from Tufts University have developed a transistor made with linen thread, which allows them to create electronic devices made entirely of fine threads that could be woven into fabric, worn on the skin, or even (theoretically) surgically implanted for diagnostic monitoring. Fully flexible electronic devices could allow a wide range of applications that conform to different shapes and allow free movement without compromising function, say the researchers.
In a study published in ACS Applied Materials and Interfaces, the authors describe the design of the first thread-based transistors (TBTs) that can be transformed into simple, all-thread-based logic circuits and ICs. The circuits replace the last remaining rigid component of many current flexible devices and, when combined with thread-based sensors, allow for the creation of fully flexible multiplex devices.
The field of flexible electronics is expanding rapidly, with most devices gaining flexibility by modeling metals and semiconductors into foldable “wavy” structures or by using inherently flexible materials such as conductive polymers. This “soft” electronics allows for applications for devices that conform and stretch with the biological tissue they are embedded in, such as the skin, heart, or even brain tissue.
However, compared to electronics based on polymers and other flexible materials, thread-based electronics have flexibility, a diversity of materials and the ability to be manufactured without the need for clean rooms, say the researchers. Thread-based electronics can include diagnostic devices that are extremely thin, soft, and flexible enough to integrate seamlessly with the biological tissues they are measuring.
Tufts engineers have previously developed a suite of wire-based temperature, glucose, strain and optical sensors, as well as microfluidic wires that can take samples or deliver drugs to surrounding tissue. The thread-based transistors developed in this study allow for the creation of logic circuits that control the behavior and response of such components. The authors created a simple small-scale integrated circuit called a multiplexer (MUX) and connected it to a thread-based sensor array capable of detecting sodium and ammonium ions, important biomarkers for cardiovascular health, liver and kidney function.
“In laboratory experiments, we were able to show how our device could monitor changes in sodium and ammonium concentrations at multiple locations,” said Rachel Owyeung, a graduate student at Tufts University School of Engineering and first author of the study. “Theoretically, we could extend the integrated circuit we made with the TBTs to connect a wide range of sensors that track many biomarkers, in many different locations using one device.”
Making a TBT (see Figure 1) involves coating a linen thread with carbon nanotubes, which create a semiconductor surface through which electrons can travel. Attached to the wire are two thin gold wires: a “source” of electrons and a “drain” from which electrons flow out (in some configurations, electrons can flow in the other direction). A third wire, called the gate, is attached to the material surrounding the wire, such that small changes in voltage across the gate wire allow a large current to flow through the wire between the source and drain, the basic principle of a transistor.
A key innovation in this study is the use of an electrolyte-infused gel as the material surrounding the wire and connected to the gate wire. In this case, the gel consists of silica nanoparticles that self-assemble into a mesh structure. The electrolyte gel (or ionogel) can be easily deposited on the wire by dip coating or rapid plugging. In contrast to the oxides or solid-state polymers used as gate material in classical transistors, the ionogel is resistant to stretching or bending.
“The development of TBTs was an important step in realizing completely flexible electronics, so that we can now turn our attention to improving the design and performance of these devices for possible applications,” said Sameer Sonkusale, professor of electrical and computer engineering at Tufts University School of Engineering and corresponding author of the study. “There are many medical applications where real-time measurement of biomarkers can be important for disease treatment and patient health monitoring. The ability to fully integrate a soft and flexible diagnostic monitoring device that the patient barely notices could be quite powerful. “
This research was supported by National Science Foundation NSF IGERT grant # DGE-1144591.
Trupti Terse-Thakoor and Hojatollah Rezaei Nejad, postdoctoral fellows in the Sonkusale laboratory, and Matthew Panzer, associate professor at Tufts University School of Engineering, also contributed to this study.
Owyeung, RE, Terse-Thakoor, T., Rezaei Nejad, H., Panzer, MJ, Sonkusale SR “Highly flexible transistor threads for all thread based integrated circuits and multiplex diagnostics.” ACS Applied Materials and Interfaces, (19 August 2019). DOI: 10.1021 / acsami.9b09522
About Tufts University
Tufts University, located on the campuses of Boston, Medford / Somerville and Grafton, Massachusetts, and Talloires, France, is recognized as one of the leading research universities in the United States. Tufts enjoys a global reputation for academic excellence and for preparing students as leaders in a wide range of professions. A growing number of innovative teaching and research initiatives span across Tufts campuses, and collaboration between faculty and students in undergraduate, graduate and professional programs in the university’s schools is widely encouraged.