Engineers at MIT have developed experimental soft, implantable optical fibers that could deliver light to major nerves to explore causes and potential treatments for peripheral nerve disorders in animal models.

(Peripheral nerve pain—from sciatica, motor neuron disease, and general numbness and pain—can occur when nerves outside the brain and spinal cord are damaged, resulting in tingling, numbness, and pain in affected limbs. Peripheral neuropathy is estimated to affect more than 20 million people in the United States.) 

“Current devices used to study nerve disorders are made of stiff materials that constrain movement, so that we can’t really study spinal cord injury and recovery if pain is involved,” says Siyuan Rao, assistant professor of biomedical engineering at the University of Massachusetts.

Optogenetics

The study is based on optogenetics, an animal research technique (originally developed at MIT) that genetically modifies neurons in the brain to respond to light. Neuroscientists have applied optogenetics in animals to precisely trace the neural pathways underlying a range of brain disorders, information that has led to targeted therapies for these conditions. 

But peripheral nerves experience constant pushing and pulling from the surrounding muscles and tissues. Rigid silicon devices would constrain an animal’s natural movement and potentially cause tissue damage.  

Testing transparent hydrogel fiber

Their new design is a soft, stretchable, transparent fiber made from hydrogel—a rubbery, biocompatible mix of polymers and water (a more Jell-O-like solution). 

The team tested the optical fibers in mice whose nerves were genetically modified to respond to blue light (to excite neural activity) or yellow light (to inhibit sciatic pain). 

“Now, people have a tool to study the diseases related to the peripheral nervous system, in very dynamic, natural, and unconstrained conditions,” said Xinyue Liu, an assistant professor at Michigan State University (MSU).

“We hope to help dissect mechanisms underlying pain in the peripheral nervous system. With time, our technology may help identify novel mechanistic therapies for chronic pain and other debilitating conditions such as nerve degeneration or injury.”

This research was supported, in part, by the National Institutes of Health, the National Science Foundation, the U.S. Army Research Office, the McGovern Institute for Brain Research, the Hock E. Tan and K. Lisa Yang Center for Autism Research, the K. Lisa Yang Brain-Body Center, and the Brain and Behavior Research Foundation.

Details of the team’s new fibers are reported today (Oct. 19, 2023), in a study appearing in Nature Methods. 

Citation: Liu, X., Rao, S., Chen, W., Felix, K., Ni, J., Sahasrabudhe, A., Lin, S., Wang, Q., Liu, Y., He, Z., Xu, J., Huang, S., Hong, E., Yau, T., Anikeeva, P., & Zhao, X. (2023). Fatigue-resistant hydrogel optical fibers enable peripheral nerve optogenetics during locomotion. Nature Methods, 1-8. c9 https://doi.org/10.1038/s41592-023-02020-9

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