Thread-based transistors: carbon nanotube coated threads carry electric current between source (S) and drain (D) wires, in response to voltate sensed at gate wire (G). (Credit: Tufts University)

A team of engineers has developed a transistor made from linen thread, enabling them to create electronic devices made entirely of thin threads that could be woven into fabric, worn on the skin, or even (theoretically) implanted surgically for diagnostic monitoring. The fully flexible electronic devices could enable a wide range of applications that conform to different shapes and allow free movement without compromising function, the researchers say.

The first thread-based transistors (TBTs) can be fashioned into simple, all-thread based logic circuits and integrated circuits. The circuits replace the last remaining rigid component of many current flexible devices, and when combined with thread-based sensors, enable the creation of completely flexible, multiplexed devices.

The field of flexible electronics is expanding rapidly, with most devices achieving flexibility by patterning metals and semiconductors into bendable “wavy” structures or using intrinsically flexible materials such as conducting polymers. These “soft” electronics are enabling applications for devices that conform and stretch with the biological tissue in which they are embedded, such as skin, heart, or even brain tissue.

However, compared to electronics based on polymers and other flexible materials, thread-based electronics have superior flexibility, material diversity, and the ability to be manufactured without the need for cleanrooms, the researchers say. The thread-based electronics can include diagnostic devices that are extremely thin, soft and flexible enough to integrate seamlessly with the biological tissues that they are measuring.

The engineers previously developed a suite of thread-based temperature, glucose, strain, and optical sensors, as well as microfluidic threads that can draw in samples from, or dispense drugs to, the surrounding tissue. The thread-based transistors developed in this study allow the creation of logic circuits that control the behavior and response of those 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.