MIT researchers have unveiled implantable, flexible fibers that use light to study and treat peripheral nerve pain. This innovative tool extends the use of optogenetics beyond the brain and has proven its efficacy in animal trials. This fiber could help test treatments for nerve-related pain.
Scientists have a new tool that can pinpoint the source of nerve pain. Engineers at MIT have developed implantable soft fibers that can carry light to the body's major nerves. When these nerves are genetically modified to respond to light, the optical fibers can send pulses of light to the nerves, suppressing pain. Optical fibers are flexible and can expand and contract with the human body.
The new fiber is an experimental tool that scientists can use to explore the causes and potential treatments for peripheral nerve disease in animal models. Peripheral neuralgia occurs when nerves outside the brain and spinal cord are damaged, causing tingling, numbness, and pain in the affected limb. It is estimated that more than 20 million people in the United States have peripheral neuropathy.
"Current devices used to study neurological diseases are made of stiff materials that restrict movement, so we can't really study spinal cord injury and recovery if pain is involved," said Siyuan Rao, assistant professor of biomedical engineering at the University of Massachusetts Amherst. "Our fibers can adapt to natural movements and do their job without restricting the subject's movement. This can give us more precise information."
"Now, people have a tool to study diseases related to the peripheral nervous system under very dynamic, natural and unconstrained conditions," added Xinyue Liu, 22, Ph.D., now an assistant professor at Michigan State University (MSU).
A research report published today (October 19) in the journal Nature Methods details their team's new fiber. Rao and Liu's MIT co-authors include Atharva Sahasrabudhe, a graduate student in the Department of Chemistry, Xuanhe Zhao, a professor in the Departments of Mechanical Engineering and Civil and Environmental Engineering, and Polina Anikeeva, a professor in the Department of Materials Science and Engineering, as well as other professors at Michigan State University, the University of Massachusetts Amherst, Harvard Medical School, and the National Institutes of Health.
Extending optogenetics beyond the brain
The new study stems from the research team's desire to expand the use of optogenetics beyond the brain. Optogenetics is a technique that uses genetic engineering to make nerves respond to light. Exposure to light can activate or inhibit nerves, providing scientists with information about how nerves work and interact with their surrounding environment.
Neuroscientists have used optogenetics in animals to precisely track neural pathways in a range of brain diseases, including addiction, Parkinson's disease, mood and sleep disorders - information that has led to targeted therapies for these diseases.
So far, optogenetics has mainly been used in the brain, a region that lacks pain receptors so that rigid devices can be implanted relatively painlessly. However, rigid devices can still damage neural tissue. The MIT team wanted to know whether this technique could be extended to nerves beyond the brain. Like the brain and spinal cord, nerves in the peripheral system can be subject to a range of injuries, including sciatica, motor neurone disease, and general numbness and pain.
Optogenetics can help neuroscientists identify the specific causes of peripheral nerve diseases and test therapies to alleviate them. But the main obstacle to implementing this technology outside the brain is movement. Peripheral nerves are constantly pushed and pulled by surrounding muscles and tissues. If a rigid silicon device is used peripherally, it limits the animal's natural movement and may cause tissue damage.
Crystals and Light
Researchers hope to develop a replacement that works and moves with the body. Their new design is a soft, stretchable, transparent fiber made from hydrogel. They tweaked the proportions of a rubbery, biocompatible polymer and water to create tiny, nanoscale polymer crystals dispersed in a more jelly-like solution.
Optical fiber consists of two layers - an inner core and an outer shell or "cladding". The team mixed the solution for each layer to create a specific crystal arrangement. This arrangement gives each layer a specific, different index of refraction.