Bioelectronic Transistors: Enabling a New Range of Capabilities With Biocompatible Electronics
Researchers at Columbia University’s (CU) School of Engineering and Applied Science have published their bioelectronics research findings. We look at the first of their two papers, which discusses their organic, biocompatible transistor technology.
The research into biocompatible electronics was led by Dion Khodagholy in collaboration with Jennifer N. Gelinas (both from CU, and respectively, an assistant professor of Electrical Engineering, and an assistant professor of Neurology).
The scientists’ R&D is two-fold: its different parts have recently been published in two papers, namely Nature Materials (NM) and Science Advances (SA). We focus on the former study below (but look out for the SA research coverage on AAC’s sister site).
Collectively, the two studies, at their crux, suggest that electronics could one day be far more compatible with the human body. But, as covered below, the NM paper chiefly explains how this is accomplished through the use of ion-driven transistors, named ‘e-IGTs’ (whereas the SA paper, in contrast, discusses the achievement of biocompatibility in relation to the researchers’ development of a highly flexible, tissue-based technology, named MCP: a mixed-conducting particulate composite material).
Introducing Bioelectronics and Their Significance
Bioelectronics is a portmanteau of ‘biology’ and ‘electronics’ and refers to various electrical components that are biocompatible, i.e. not toxic to living tissue.
In opposition to traditional electronic devices (whose component properties are unsuited to human cells and therefore need to be housed within the right enclosures to be used as implantables), bioelectronic devices don’t need to be protectively encased to function. Rather, they are organic in form and can be more practically and safely implanted as a result.
A close-up of a pacemaker in someone’s left hand. Note the metal enclosure and consider the issues that arise from using such thick material as part of an implantable
The CU researchers elaborate on those two extremes by citing the improvement that would come from replacing traditional pacemakers and other MedTech with organic equivalents. Said Khodagholy: “Instead of having large implants encapsulated in thick metal boxes to protect the body and electronics from each other, … we could do so much more if our devices were smaller, flexible, and inherently compatible with our body environment.”
Alongside this, there are obviously many other flawed implantable devices—medical and otherwise—that would also be greatly improved by becoming organic and therefore biologically compatible.
The Intentions and Accomplishments of CU’s Research
To quote the abstract of the NM paper (published 16th March 2020), the CU researchers’ intentions were to “create soft, biocompatible, long-term implantable neural processing units”.
Accordingly, the below-pictured ‘e-IGTs’ (conformable enhancement-mode, internal ion-gated organic electrochemical transistors) were constructed in the interest of obtaining a broad range of the wearer’s electrophysiological signals.
The Materials Science Involved
The fundamental upshot of this biocompatibility is that the wearer’s epileptic discharges and other neurological issues may be monitored in real-time for medical analysis; however, we’ll look at the other (engineering-focused) implications of CU’s innovation later.
The success of the electrochemical transistors in bioelectronics was chiefly down to the researchers’ focus on the materials science involved, particularly their interest in circumventing traditional transistors in favor of their own substitute technology: the said ‘e-IGTs’. As Columbia Engineering’s article explains:
“[A]lthough they [conventional transistor-based devices] work well with electrons, they are not very effective at interacting with ionic signals, which is how the body’s cells communicate. As a result, these properties restrict the abiotic/biotic coupling to capacitive interactions only on the surface of material, resulting in lower performance. Organic materials have been used to overcome these limitations as they are inherently flexible.”
The Use of Organic Materials
Aside from their ability to avoid the need for implant-protecting enclosures, such ‘organic materials’ were also chosen due to their electronic and ionic conduction. In fact, the e-IGTs have “embedded mobile ions inside their channels” [emphasis added]. The CU literature explains that the result is a more efficient ion transit process, a high transconductance and a gain-bandwidth “that is several orders of magnitude above that of other ion-based transistors”.
Such a makeup means that the e-IGTs are highly receptive to the wearer’s biological ions, namely the ions that a person’s cells use to communicate neurological information. Plus, the material, to reiterate, can be much more safely and practically implanted within the body, due to the fact that it doesn’t require an enclosure to be biologically compatible.
A photograph of someone’s left hand, on which their palm is covered with Columbia University’s thin bioelectronic transistors, named ‘e-IGTs’. The middle of the photograph is annotated with a top-down view (captured using a micrograph) of one of the e-IGTs. Image credited to Columbia Engineering
The Research Implications
Alongside what this study could mean for neurological illness research, the engineering implications are of course also significant.
Alongside the crucial benefits to the field of neurology, the Columbia University researchers believe that other advantages may be realized by the discovery of e-IGTs (they have also cited wearable miniaturized sensors, for instance).
From a design perspective, furthermore, the advantages of e-IGTs are likewise prominent. At a time when the importance of component miniaturization is at an all-time high, soft and flexible electronics—unaffected by the need for invasive enclosures and other rigid components—are a welcome contribution to manufacturing.
This is especially true when you consider the ease of reproducibility that comes with such an organic technological makeup: “e-IGTs”, write the CU researchers, “can be manufactured in large quantities and are accessible to a broad range of fabrication processes”.
All in all, there are countless applications that would benefit from Columbia University’s transistor technology, and its manufacturability—and suitability for the increasingly-needed field of biocompatible devices—shows clear promise for future electronics.