Developing soft and flexible biocompatible electronic devices

Developing soft and flexible biocompatible electronic devices
© iStock/Jan-Otto

Currently, medical devices used for pacemakers and implants are clunky, rigid, and non-biocompatible. Now, scientists are one step closer to developing soft and flexible biocompatible electronic devices.

The design of current devices has been severely constrained by the rigid, non-biocompatible electronic components needed for safe and effective use and solving this challenge would open the door to a broad range of new therapies.

Scientists are now focussing on developing bioelectronic devices that are not only fast, sensitive, biocompatible, soft, and flexible, but also have long-term stability in physiological environments such as the human body.

These devices would greatly improve human health, from monitoring in-home wellness to diagnosing and treating neuropsychiatric diseases, including epilepsy and Parkinson’s disease.

Biocompatible electronic devices

In collaboration with Jennifer Gelinas, Department of Neurology, and the Institute for Genomic Medicine at Columbia University Irving Medical Center, Dion Khodagholy, assistant professor of electrical engineering, has recently published two papers looking at biocompatible devices.

The first in Nature Materials covers ion-driven soft and organic transistors that he and Gelinas have designed to record individual neurons and perform real-time computation that could facilitate diagnosis and monitoring of neurological disease.

The second paper, published in Science Advances, demonstrates a soft, biocompatible smart composite, which is an organic missed conducting particulate material (MCP) that enables the creation of complex electronic components which traditionally require several layers and materials, and which also enable easy and effective electronic bonding between soft materials, biological tissue, and rigid electronics.

Because the composite is fully biocompatible and has controllable electronic properties, MCP can non-invasively record muscle action potentials from the surface of arm and large-scale brain activity during neurosurgical procedures to implant deep brain stimulation electrodes.

Khodagholy, who directs the Translational NeuroElectronics Lab at Columbia Engineering, said: “Instead of having large implants encapsulated in thick metal boxes to protect the body and electronics from each other, such as those used in pacemakers, and cochlear and brain implants, we could do so much more if our devices were smaller, flexible, and inherently compatible with our body environment.

“Over the past several years, my group has been working to use unique properties of materials to develop novel electronic devices that allow efficient interaction with biological substrates – specifically neural networks and the brain.”

Utilising organic materials

Conventional transistors are made out of silicon, which means they need to be encased in metal or plastic within the body as they cannot function in the presence of ions and water – eventually breaking down because of ion diffusion into the device. The devices are also are not effective at interacting with ionic signals, which is how the body’s cells communicate and, 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, but the electrical performance of these devices was not sufficient to perform real-time brain signal recording and processing.

Khodagholy’s team took advantage of both the electronic and the ionic conduction of organic materials to create ion driven transistors which they call e-IGTs, or enhancement-mode, internal ion-gated organic electrochemical transistors, that have embedded mobile ions inside their channels.

Because the ions do not need to travel long distances to participate in the channel switching process, they can be switched on and off quickly and efficiently.

“We’re excited about these findings,” says Gelinas. “We’ve shown that E-IGTs offer a safe, reliable, and high-performance building block for chronically implanted bioelectronics, and I am optimistic that these devices will enable us to safely expand how we use bioelectronic devices to address neurologic disease.”

Mimicking biological networks

Inspired by electrically active cells the team created a single material capable of performing multiple, non-linear, dynamic electronic functions just by varying the size and density of its composite mixed-conducting particles.

Khodagholy said: “This innovation opens the door to a fundamentally different approach to electronic device design, mimicking biological networks and creating multifunctional circuits from purely biodegradable and biocompatible components.”

Both the E-IGTs and MCP hold great promise as critical components of bioelectronics, from wearable miniaturised sensors to responsive neurostimulators.

The E-IGTs can be manufactured in large quantities and are accessible to a broad range of fabrication processes. Similarly, MCP components are inexpensive and easily accessible to materials scientists and engineers. In combination, they form the foundation for fully implantable biocompatible devices that can be harnessed both to benefit health and to treat disease.

Khodagholy and Gelinas are now working on translating these components into functional long-term implantable devices that can record and modulate brain activity to help patients with neurological diseases such as epilepsy.

“Our ultimate goal is to create accessible bioelectronic devices that can improve peoples’ quality of life,” says Khodagholy, “and with these new materials and components, it feels like we have stepped closer to that.”

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