Flexible devices from thread

Departments - Medical Innovations

Transistors and integrated circuits made from threads combine with thread-based sensors to create fully flexible devices.

Manufacture of thread based transistors (TBTs): a) Linen thread b) Attachment of source (S) and drain (D) thin gold wires c) Drop casting of carbon nanotubes on the surface of the thread d) Application of electrolyte-infused gel (ionogel) gate material e) Attachment of the gate wire (G) f) Cross-sectional view of TBT. Electrolytes: EMI: 1-ethyl-3methylimidazolium; TFSI: bis(trifluoromethylsulfonyl)imide

Electronic devices made entirely of thin linen threads could be woven into fabric, worn on the skin, or even surgically implanted for diagnostic monitoring. Fully flexible electronic devices could conform to different shapes, allowing free movement without compromising function.

Developed by Tufts University researchers, thread-based transistors (TBTs) can be fashioned into simple, all thread-based logic circuits and integrated circuits, replacing the last rigid component of many flexible devices. Coupled with thread-based sensors, TBTs enable flexible, multiplexed devices.

Source (S) and drain (D) wires are tied to carbon nanotube coated thread, dipped in an electrolytic gate gel. A gate wire is connected to the gel to trigger flow of electrons through the transistor when the gate is above a threshold voltage.

Thread-based electronics are more flexible than polymers with greater material diversity and can be manufactured without cleanrooms. Electronics could include extremely thin, soft, and flexible diagnostic devices that integrate seamlessly for measuring biological tissues.

Tufts engineers previously developed thread-based temperature, glucose, strain, and optical sensors and microfluidic threads that draw in samples from, or dispense drugs to, surrounding tissue. Thread-based transistors create logic circuits that control the components’ behavior and response.

Researchers created a small-scale multiplexer (MUX) integrated circuit and connected it to a thread-based sensor array that detects sodium and ammonium ions – biomarkers for cardiovascular health and liver and kidney function.

Researchers coated a linen thread with carbon nanotubes to create a semiconductor surface through which electrons can travel to create the TBT. Two thin gold wires provide a source of electrons and a drain where the electrons flow out (in some configurations, the electrons can flow in the other direction). A third wire, the gate, attaches to material surrounding the thread, and small voltage changes through the gate wire allow a large current to flow through the thread between the source and drain – the basic principle of a transistor.

A critical innovation in this study is an electrolyte-infused gel used as the material surrounding the thread and connected to the gate wire. Silica nanoparticles in the gel self-assemble into a network structure. The electrolyte gel (ionogel) can easily be deposited onto the thread by dip coating or rapid swabbing. Solid-state oxides or polymers used as gate material in classical transistors are less resilient to stretching or flexing.

Sameer Sonkusale, professor of electrical and computer engineering at Tufts University School of Engineering and corresponding author of the study says, “There are many medical applications in which real-time measurement of biomarkers can be important for treating disease and monitoring the health of patients. The ability to fully integrate a soft and pliable diagnostic monitoring device that the patient hardly notices could be quite powerful.”

Tufts University

The research was funded by Nanostructures for Electrical Energy Storage, a DOE Energy Frontier Research Center, and by Intramural Research Program of the NIDDK (DK043304)