A coin-sized biodegradable widget could end back pain

Nerve damage affects millions of people. The symptoms can range from mild pins and needles, to numbness, to a partial loss of mobility.

The cures are perhaps worse than the condition. Invasive grafting procedures or direct electrical stimulation are the norm, and these therapies can be as ineffective and difficult to perform as they are unpleasant to experience.

But the tide may be about to turn for sufferers of one of the most common kinds of nerve pain — back pain. Scientists in China have developed a leave-it-and-forget-it approach to electrical stimulation, providing self-powered stimulation to treat one of the top sources of back pain without the need for additional surgeries.

What's new — Part of the beauty of this innovation lies in its ease of use. In a study on rats with sciatic nerve damage, the researchers found their biodegradable stimulator restored motor function and promoted nerve regeneration as well as existing techniques, but with far less hassle.

By providing long-term electrical stimulation via a tiny, biodegradable cuff fitted around the damaged nerve, the team hopes their approach can improve upon electrical stimulation therapy and dramatically reduce multiple surgeries:

"We report a biodegradable, self-electrified, and ultraminiaturized conduit device for promoting peripheral nerve regeneration, which simultaneously offers structural guidance and sustained electrical cues in the biological systems," explain the authors in their paper. "The entire device is fully biocompatible and biodegradable in physiological environments, eliminating secondary surgeries for retrieval."

The findings were published Friday in the journal Science Advances.

The big idea — The sciatic nerve stretches all the way from your lower back down either leg. It is the longest nerve in the body, and it can be easily damaged by back problems like a herniated disk — which can push on the nerve and can cause pain — or extra bone growth such as bone spurs. It can also be damaged by poor exercise technique. But whatever the source of the problem, sciatic nerve damage can generate radiating, debilitating pain which shoots down a person's back and legs.

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The idea behind this new approach is to provide electrical stimulation to the nerve as a way to regenerate lost nerve cells and promote improved motor function and movement. Electrical stimulation has been used previously in humans but can be tricky to do on the nerve site. Existing stimulation techniques are also not self-powered and in turn, could require multiple sessions — potentially raising the risk of irritation to the surgery site.

How it works — To test their device, the team tried it out in several rats with sciatic nerve damage.

The device is smaller than a quarter and made of a dissolvable, battery-like cell with embedded electrodes that fit around damaged nerves —much like a cast or splint around a break — guiding their regrowth. When nerve cells receive electrical stimulation, they release a biochemical to promote nerve cell growth and recovery.

These tiny casts were wrapped around the sciatic nerves of the rats which had a 10-millimeter gap in their sciatic nerve, causing them significant mobility issues. In humans, such damage to our sciatic nerve could cause tingling, numbness, and weakness in the legs, affecting our ability to walk, run, or play sports.

And perhaps most importantly, the authors write, this device can non-toxically dissolve into the body, eliminating the need for a second surgery to retrieve it.

To get a sense of how the device stacks up to the current therapies available, the researchers compared it to a 'control' cuff with no electrical stimulation, and a more typical grafting procedure.

What they discovered — The cuff creates a continuous electric field for two to three days around the damaged nerve endings. To assess how it worked over the longterm, the researchers examined tissue regeneration progress and recovery in the rats at weeks three, nine, and twelve after implantation.

Rats which were fitted with the new devices recovered their motor function to a similar degree as the group which underwent the typical grafting procedure. The rats also had better sciatic nerve function than rats with the 'control' cuff.

Interestingly, the researchers found a critical period for treatment that could help improve therapies for back pain across the board. The first few days of treatment seemed most crucial for nerve regeneration and motor-function recovery over the long term. This result suggests the device could help reduce the total time muscles experience nerve depletion.

What's next — This study is in rats, so while it is promising, it is not the silver bullet back-pain sufferers everywhere are looking for yet. More preliminary research needs to be done before the device can be trialed in humans, the authors write. The operating life of the device also needs to be improved, and the intensity of the electrical stimulation tweaked, the authors say.

But if it does bear out in further experiments, it may be possible to use the device in conjunction with traditional grafting treatments for even better results, according to the study.

Ultimately, the researchers behind this study hope their work can be an "enabling innovative approach to tackle the hurdles in regenerative medicine."

Abstract: Peripheral nerve regeneration remains one of the greatest challenges in regenerative medicine. Deprivation of sensory and/or motor functions often occurs with severe injuries even treated by the most advanced microsurgical intervention. Although electrical stimulation represents an essential nonpharmacological therapy that proved to be beneficial for nerve regeneration, the postoperative delivery at surgical sites remains daunting. Here, a fully biodegradable, self-electrified, and miniaturized device composed of dissolvable galvanic cells on a biodegradable scaffold is achieved, which can offer both structural guidance and electrical cues for peripheral nerve regeneration. The electroactive device can provide sustained electrical stimuli beyond intraoperative window, which can promote calcium activity, repopulation of Schwann cells, and neurotrophic factors. Successful motor functional recovery is accomplished with the electroactive device in behaving rodent models. The presented materials options and device schemes provide important insights into self-powered electronic medicine that can be critical for various types of tissue regeneration and functional restoration.