MIT’s soft fiber implants could offer drug-free pain relief

The United States suffered from a growing opioid epidemic for over 20 years. Opioids are easy to get, they’ve often been too easily prescribed, and it’s hard to understate the scale of the problem. Every week, 1,500 people will die from some kind of opioid misuse. Opioids – primarily now illicit fentanyl – represent a problem not only for public health, but for the economy, and even national security. Last year, the U.S. Joint Economic Committee estimated that opioid addiction and overdose cost the United States nearly $1.5 trillion in 2020.

But the opioid epidemic began, in part, with a good intention to treat a real problem: A lot of people are in pain, often chronic and sometimes debilitating. So there’s a need for painkillers. The CDC sees the opioid crisis in terms of “waves.” The first wave began when well-intentioned physicians were prescribing lots pain relievers, which helped to fuel opioid addiction. A crackdown on painkiller prescriptions reduced overdoses on pills but led to a transition to illicit heroin, and then from heroin to the exceptionally deadly fentanyl.

The challenge, then, is to find painkillers that are as effective as opioids, but without the high or addictive side effects. It’s a challenge with many contenders. At the time of writing, there are 16 non-opioid pain-relief drugs that are currently in phase III trials. Each has limitations, and they often have narrow use cases.

Now, thanks to engineers at MIT, we can add a new and exciting possibility to the roster.

Peripheral neuropathy

More than 20 million people in the United States suffer from peripheral neuropathy. This is when the peripheral nerves, outside of the brain and spinal cord, are damaged or malfunctioning, sometimes misreporting pain signals from parts of the body. For instance, a construction worker who has used power tools for decades might experience chronic tingling in their hands during retirement. Or a diabetic might feel constant burning pain in their feet, without any trauma, because the nerves have been damaged by high blood sugar. Peripheral neuropathy can be a terrible condition; it’s not only painful in itself, but its chronic nature can exhaust patients’ endurance and mental health.

For the last few decades, without an easy or effective cure, we have treated peripheral neuropathy with drugs, often with opioids for the worst afflicted. The main non-pharmaceutical alternative has been rigid nerve implants. The problem is that their rigidity massively constrains movement. Worse than that, overly rigid nerve implants can sometimes cause further damage. 

Soft fibers provide pain relief.

Earlier this month, a team from MIT released a paper outlining a new, hopeful alternative. Lie et al have developed soft implantable fibers designed to deliver pulses of light to major peripheral nerves. In mice, the sciatic nerve was genetically engineered to respond to specific wavelengths of light, either causing the nerves to fire (blue light) or inhibit signals (yellow light).

They found that the implant’s yellow light pulses, which reduced nerve activity, also inhibited pain in the mice.

“We are focusing on the fiber as a new neuroscience technology,” said first author Xinyue Liu. “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.”

The optical fibers are made from a rubbery mix of polymers and water, in a unique two-layered structure. This design ensures the efficient transmission of light through the fibers without loss or scattering – an essential requirement for effective interaction with nerves.

The team even proved how robust and functional the fibers were: they were still working after months of strenuous exercise and movement by the animals.

Of course, there are qualifications. These experiments were conducted in mice, and the stress tests involved 30,000 rotations of an exercise wheel. To turn this experiment into something that can treat pain in people will take further research and experimentation. But the researchers believe that this innovative tool is the first step in unlocking a deeper understanding of peripheral nerve disorders in animals, which could, in turn, cascade into human applications.

And those potential applications are legion. As the paper puts it, “Our method can be further leveraged to investigate motor control, somatosensation, and pain processing. Beyond the application in sciatic nerves, the hydrogel fibers can be tailored for implantation in peripheral nerves, as well as on other motile organs, such as the heart, gut, and blood vessels.”