Biocompatible Transistor Invented for New Devices

A new ion-driven transistor that is biocompatible and thus safe for use within the human body for bioelectronic applications.

Researchers have developed what they said is the first biocompatible ion-driven transistor fast enough to enable real-time signal sensing and stimulation of brain signals.

A team led by Dion Khodagholy, assistant professor of electrical engineering at Columbia University’s engineering department, invented what’s called an internal-ion-gated organic electrochemical transistor (IGT). The device operates via mobile ions that are contained within a conducting polymer channel to enable both volumetric capacitance—or ionic interactions involving the entire bulk of the channel—and as well as shortened ionic transit time.

An internal-ion-gated organic electrochemical transistor (IGT) developed by a team at Columbia University shown conforming to the petals of an orchid. Researchers there developed a novel device that paves the way for new and more complex bioelectronic devices and applications. (Image source: Columbia University)

Bioelectronic Devices

“Current transistors do not have all the features required for safe, reliable operation in physiologic environments, like the human body, over extended periods of time,” explained Columbia postdoctoral research fellow George Spyropoulos. “We aim to design and develop transistors that fulfill all these requirements and enable construction of safer, smaller, and smarter bioelectronic devices.”

The IGT the team developed has large transconductance, or amplification rate, can function at a high speed, and can be independently gated as well as microfabricated to create scalable conformable integrated circuits, researchers said.

“To make the device fast we modified the material to have its own mobile ions,” Spyropoulos told Design News. “This way the distance ions required to travel is shortened to within the polymer structure. This improved the speed of the transistor by an order of magnitude compare to other ionic devices with the same size.”

Sugar is the Secret

Moreover, the device is made completely of biocompatible material—specifically, an every-day product found in people’s favorite desserts.

“Our secret ingredient is sugar,” Spyropoulos said. “Sugar molecules help the transistor channel to stay hydrated, makes the traveling of the ions easier and faster.”

In their work—outlined in a paper published in Science Advances—researchers demonstrate the device’s ability to provide a small, conformable interface with human skin that uses local amplification to record high-quality neural signals and is suitable for advanced data processing.

Transistors for bioelectronics devices already exist. However, to date researchers have not been able to build transistors that have all the features needed for safe, reliable, and fast operation in the complex and sensitive environment of the human body, Spyropoulos explained.

Safer Inside the Body

“In the past, traditional silicon-based transistors were used in bioelectronic devices, but they have to be carefully encapsulated to avoid contact with body fluids—both for the safety of the patient and the proper operation of the device,” he said. “This makes implants based on these transistors bulky and rigid.”

The Columbia team’s invention now paves the way for a new generation of bioelectronics devices that can record body signals as well as process them, detect patterns, and deliver electrical or chemical stimulation to address problems, Spyropoulos said.

The team demonstrated use of the ICT it developed to record human brain waves and perform an electroencephalography (EEG) from the surface of the scalp, and found it was easy to apply to the scalp and did not cause any irritation, he said.

“It was much smaller than any other EEG electrodes, making it possible to fit between human hairs, improving the application process and the signals that can be recorded,” Spyropoulos explained.

He said the team is “very excited” about its invention and believe what they’ve developed has numerous applications, including ones that can replace current devices used to treat some forms of epilepsy with ones that are smaller and easier to implant, among many others.

“With such speed and amplification, combined with their ease of microfabrication, these transistors could be applicable to many different types of devices,” Spyropoulos said. “We are excited also about the potential to use these devices to benefit patient care in the future.”

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco and New York City. In her free time she enjoys surfing, traveling, music, yoga and cooking. She currently resides in a village on the southwest coast of Portugal.

 

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