Researchers invent soft, bioelectronic sensor implant

Researchers at the University of California, Irvine and New York’s Columbia University have embedded transistors in a soft, conformable material to create a biocompatible sensor implant that monitors neurological functions through successive phases of a patient’s development.

In a paper published recently in Nature Communications, the UC Irvine scientists describe their construction of complementary, internal, ion-gated, organic electrochemical transistors that are more amenable chemically, biologically and electronically to living tissues than rigid, silicon-based technologies. The medical device based on 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,” says 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 have been composed of different materials to account for different polarities of signals, which, in addition to being unyielding and cumbersome, present the risk of toxicity when implanted in sensitive areas. The team of researchers from UC Irvine and Columbia University worked around this problem by creating its transistors in an asymmetric fashion that 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,” says 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.”

He added that arraying transistors into a smaller, single-polymer material greatly simplifies the fabrication process, enabling large-scale manufacturing and opportunities to expand the technology beyond the original neurological application to almost any biopotential processes.

Khodagholy, who heads the UC Irvine Translational Neuroelectronics Laboratory, which recently moved to Irvine from Columbia University, says his team’s work has the added benefit of scalability: “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.”

Another advantage highlighted in the Nature Communications paper is the device can be implanted in a developing animal and withstand transitions in tissue structures as the organism grows, something that is not possible with hard, silicon-based implants.

“This characteristic will make the device particularly useful in pediatric applications,” says 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,” Khodagholy says. Complementary, internal, ion-gated, organic electrochemical transistors “will substantially broaden the application of bioelectronics to devices that have traditionally relied on bulky, nonbiocompatible components.”

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