Researchers develop bioelectronic sensor implant

The transistors in question were constructed by the researchers and are complementary, internal, ion-gated, organic electrochemical transistors that are more amenable chemically, biologically, and electronically to living tissues compared with conventional, rigid, silicon-based technologies. 

The device created based off of these transistors can function in sensitive parts of the body and conform to organ structures, even as they grow.

“Advanced electronics have been in development for several decades now, so there is a large repository of available circuit designs. The problem is that most of these transistor and amplifier technologies are not compatible with our physiology,” explained co-author Dion Khodagholy, Henry Samueli Faculty Excellence Professor in UC Irvine’s Department of Electrical Engineering and Computer Science. “For our innovation, we used organic polymer materials that are inherently closer to us biologically, and we designed it to interact with ions, because the language of the brain and body is ionic, not electronic.”

In standard bioelectronics, complementary transistors are composed of different materials, in order to account for the different polarities of signals. These transistors are not only unyielding, which makes them incompatible for organic implantation, but also present the risk of toxicity when implanted in sensitive areas.

The researchers addressed this problem by creating transistors in an asymmetric fashion which enables them to be operated using a single, biocompatible material.

“A transistor is like a simple valve that controls the flow of current. In our transistors, the physical process that controls this modulation is governed by the electrochemical doping and de-doping of the channel,” said first author Duncan Wisniewski, Columbia University Ph.D. candidate during the project who is now a visiting scholar in the UC Irvine Department of Electrical Engineering and Computer Science. “By designing devices with asymmetrical contacts, we can control the doping location in the channel and switch the focus from negative potential to positive potential. This design approach allows us to make a complementary device using a single material.”

Arraying transistors into a smaller, single-polymer material simplifies the fabrication process, which suggests it can be increased into larger scale manufacturing and presents opportunities to expand the technology beyond the original neurological application to other biopotential processes.

“You can make different device sizes and still maintain this complementarity, and you can even change the material, which makes this innovation applicable in multiple situations,” added Khodagholy.

The device can also be implanted into a developing animal and withstand transitions in tissue structures as the organism grows - something that is not possible when using hard, silicon-based implants.

“This characteristic will make the device particularly useful in pediatric applications,” said co-author Jennifer Gelinas, UC Irvine associate professor of anatomy and neurobiology as well as pediatrics, who’s also a physician at Children’s Hospital of Orange County.

“We demonstrated our ability to create robust complementary, integrated circuits that are capable of high-quality acquisition and processing of biological signals,” said Khodagholy. Complementary, internal, ion-gated, organic electrochemical transistors “will substantially broaden the application of bioelectronics to devices that have traditionally relied on bulky, non-biocompatible components.”

Along with Khodagholy, Gelinas and Wisniewski, Claudia Cea, Liang Ma, Alexander Ranschaert, Onni Rauhala and Zifang Zhao of Columbia University were all part of the project. The work was supported by the National Institutes of Health and the National Science Foundation.