Artificial nerve with organic transistor design shows promise for brain-machine interfaces

In recent years, many engineers have been trying to develop hardware components that could emulate the functions of various biological systems, including synapses, the human skin and nerves. These bio-inspired systems include what are referred to as artificial nerves, systems designed to emulate the role of nerves in the body of humans and other animals.

Artificial nerves could be useful for a wide range of applications, ranging from systems for repairing damaged nerves to brain-computer interfaces, highly precise sensors and other advanced electronics. So far, however, the engineering of nerve-inspired systems that operate at biologically compatible frequencies and realistically replicate the function of nerves has proved challenging.

Researchers at Xi’an Jiaotong University in China and Technical University of Munich recently developed a new high-frequency artificial nerve with a unique design that optimizes the transport of ions and electrons, while also rapidly responding to signals and retaining charge-related information. This nerve-inspired system, introduced in a paper published in Nature Electronics, is based on homogenously integrated organic electrochemical transistors.

“N-type organic electrochemical transistors are a possible building block for artificial nerves, as their positive-potential-triggered potentiation behavior can mimic that of biological cells,” wrote Shijie Wang, Yichang Wang and their colleagues in their paper. “However, the devices are limited by weak ionic and electronic transport and storage properties, which leads to poor volatile and non-volatile performance and, in particular, a slow response. We describe a high-frequency artificial nerve based on homogeneously integrated organic electrochemical transistors.”

The artificial nerves developed by this team of researchers are based on vertical n-type organic electrochemical transistors that were sequentially deposited onto a substrate. These devices can emulate the functioning of receptors, synapses and somas in the human nervous system, ultimately producing nerve-like circuits.

“We fabricate a vertical n-type organic electrochemical transistor with a gradient-intermixed bicontinuous structure that simultaneously enhances the ionic and electronic transport and the ion storage,” wrote Wang, Wang and their colleagues. “The transistor exhibits a volatile response of 27 μs, a 100-kHz non-volatile memory frequency and a long state-retention time.”

Artificial nerves introduced in the past were found to excel in some domains (e.g., ionic and electronic transport, long-term memory storage, etc.), while achieving sub-optimal results in others. In contrast, the organic transistor-based system created by the researchers was found to attain both good ionic and electronic transport, as well as long-term ion storage, thus reaching beyond previously reported trade-offs.

“Our integrated artificial nerve, which contains vertical n-type and p-type organic electrochemical transistors, offers sensing, processing and memory functions in the high-frequency domain,” wrote the researchers. “We also show that the artificial nerve can be integrated into animal models with compromised neural functions and that it can mimic basic conditioned reflex behavior.”

To assess the potential of their artificial nerve, the researchers implanted it in mice with impaired neural functions. Their initial findings were very promising, as the system was found to be compatible with the mice’s biological tissues, while also effectively mimicking conditioned nerve-supported reflexes.

In the future, this promising artificial nerve could be improved further and tested in a broader range of experiments to further assess its safety and performance. Eventually, it could be used to develop technologies for repairing nerve circuits, as well as brain-computer interfaces, such as prosthetic limbs that can be controlled by the brain, devices that allow paralyzed patients to easily communicate with others and systems to precisely monitor or manipulate brain activity.

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