Can a human with a spinal cord injury walk and run? Discovering clues to solving science challenges with neuromorphic technology

An international research team led by Prof. Tae-Woo Lee (Department of Materials Science and Engineering, Seoul National University, Republic of Korea) and Prof. Zhenan Bao (Department of Chemical Engineering, Stanford University, US) has succeeded in recovering muscle movements in a model of paralyzed mice through organic artificial nerves. The result was published in the world-renowned international journal ‘Nature Biomedical Engineering’ on 08/16.

The nerves, which are essential for life activities as well as have a significant impact on quality of life, are easily damaged by various causes such as physical injury, genetic causes, secondary complications, and aging. In addition, as once nerves are damaged it is difficult to be reconstructed, some or all their bodily functions are permanently lost due to poor bio-signaling. The painful story of a celebrity’s spinal cord injury is sometimes told in the media. The medical challenge of nerve damage, which has been experienced with the birth of mankind, remained a scientific challenge despite the development of drastic medicine and biology, and there seems to be no big clue in the future. Various attempts have been made to treat damaged nerves, including surgical methods and medication, but damaged or degenerated nerve functions remain almost impossible to recover.

Among the various methods for rehabilitation in patients with neurological damage, Functional Electrical Stimulation (FES), which is currently actively used in clinical practice, uses computer-controlled signals. Through this, electrical stimulation is applied to muscles that are no longer arbitrarily controllable in patients with neuropathy to induce muscle contraction, resulting in functionally useful movements in the biological body even though they are confined in a specific space. However, those conventioal approach has limitations that patients are not suitable for long-term use in their daily lives because they involve complex digital circuits and computers for signal processing to stimulate muscles, consuming a lot of energy and poor biocompatibility in the process.

To solve the problem, the research team succeeded in controlling the leg movement of mice only with artificial nerves without a complex and bulky external computer using stretchable, low-power organic nanowire neurormorphic device that emulates the structure and function of bio nerve fibers. The stretchable artificial nerve consists of a strain sensor that simulates a proprioceptor which detects muscle movements, an organic artificial synapse that simulates a biological synapse, and a hydrogel electrode for transmitting signals to the leg muscles.

The researchers adjusted the movement of the mouse legs and the contraction force of the muscles according to the firing frequency of the action potential transmitted to the artificial synapse with a principle similar to that of the biological nerve, and the artificial synapse implements smoother and more natural leg movements than the usual FES.

In addition, the artificial proprioceptor detects the leg movement of the mouse and gives real-time feedback to the artificial synapse to prevent muscle damage due to excessive leg movement.

The researchers succeeded a paralyzed mouse to kick the ball or walk and run on the treadmill. Furthermore, the research team showed the applicability of artificial nerves in the future for voluntary movement by sampling pre-recorded signals from the motor cortex of moving animals and moved the legs of mice through artificial synapses.

The researchers discovered a new application feasibility in the field of neuromorphic technology, which is attracting attention as a next-generation computing device by emulating the behavior of a biological neural network. The researchers demonstrated that the neuromorphic field will be used not only in computing but in various fields such as biomedical engineering and biotechnology.

     Prof. Tae-Woo Lee said, “Neural damage is still considered a big scientific challenge from the past to the present despite the remarkable advances in medicine, and without a new breakthrough, it will still remain a hard-to-solve problem in the future. This research provides a new breakthrough in overcoming nerve damage in an engineering way using neuromorphic technology, not in a biomedical way” expressing the significance of the study. He also added, “An engineering approach to overcoming nerve damage will open a new path to improving the quality of life for those suffering from related diseases and disorders.”

Prof. Zhenan Bao, noted the potential of the study, saying, “Through the development of stretchable artificial nerves for nerve-damaged patients, it has provided a cornerstone for patient-friendly, more practically usable wearable neural prosthetics, away from the existing form factor.” Through this, she raised expectations that “The source technology of the stretchable artificial nerve may be applied to various medical wearable technologies.”

In the future, the research team showed a willingness to continuously conduct the study for clinical application beyond primates as well as rodents such as mice. Through this, it seems possible to present new solutions and strategies for nerve damage in humans such as spinal cord injury, peripheral nerve damage, and neurological damage such as Lou Gehrig, Parkinson’s, and Huntington’s disease.