An implantable electronic device that can heal injured peripheral nerves by stimulating them with electric pulses before the body biodegrades and absorbs it has shown successful results in preliminary tests.
A study led by Washington University School of Medicine in St. Louis, MO, and Northwestern University in Evanston, IL, reveals that the device — which is no bigger than a quarter — helped rats rapidly regenerate nerves in their legs.
The rats regained the use of their nerves and strength in their muscles in the several days before their bodies completely broke down and absorbed the biodegradable device.
The purpose of the innovation is to speed up recovery in peripheral nerve injury cases that are treated with electrical stimulation during surgery.
"We know," notes co-senior study author Dr. Wilson Z. Ray, an associate professor of neurological and orthopedic surgery at Washington University, "that electrical stimulation during surgery helps, but once the surgery is over, the window for intervening is closed."
In a paper on the study, which is to appear in the journal Nature Medicine, he and his colleagues demonstrate how the electronic device extends the intervention window.
"With this device, we've shown that electrical stimulation given on a scheduled basis can further enhance nerve recovery," he adds.
Peripheral nerves can regenerate
Peripheral nerves run through the torso, arms, and legs. They are different from nerves in the spinal cord in that their cells and tissue can regrow after damage.
Injury to peripheral nerves causes tingling, numbness, pain, and muscle weakness. With medication and physical therapy, some injuries can heal in weeks, while others can take months.
Severe cases, however, often require surgery, and there are few ways of speeding up recovery.
Estimates now suggest that peripheral nerve damage as a result of trauma and medical conditions affects around 20 million people in the United States and incurs an annual healthcare bill of $150 billion.
In cases treated with surgery, it is standard practice to give electrical stimulation because it helps nerve cells regrow and completely heal damaged tissue by triggering the release of growth promoters.
Better, faster recovery with more stimulation
The electronic implant is wrapped around a damaged nerve and, over a few days, stimulates it with regular pulses before being harmlessly broken down and absorbed by the body.
To deliver the impulses, it takes power from an external wireless charger that works similarly to the "mats" that can charge cell phones wirelessly.
The researchers tested it on rats with sciatic nerve injuries. The sciatic nerve is the largest nerve in the human body. It carries signals up and down the lower limbs and controls muscles such as the hamstrings and others in the legs and feet.
The device sent pulses in the rats' damaged sciatic nerves for 1 hour every day. The animals were in three groups: one had this dose of electrical stimulation for 1 day, another for 3 days, and the third for 6 days. There were also some that received none, for comparison.
Over the following 10 weeks, the team saw that any amount of stimulation was more effective at restoring muscle strength and mass than none. Recovery of nerve signals and muscle strength was more rapid and complete, however, the more days of stimulation the animals received.
The scientists can control the exact number of days the device operates for before it biodegrades by altering properties such as material thickness and composition.
"Before we did this study, we weren't sure that longer stimulation would make a difference, and now that we know it does we can start trying to find the ideal time frame to maximize recovery."
Dr. Wilson Z. Ray