An injectable electrode could prove a better way to ease chronic nerve pain than opioid painkillers or bulky and expensive implants, animal research suggests.
It's called an "injectrode." It appears easier and cheaper than spinal implants for debilitating back pain, and safer than long-term use of opioids like OxyContin, or oxycodone, a recent paper suggests.
A liquid silicone gel filled with small metal particles is injected around the nerve that's causing the pain, said researcher Kip Ludwig, a professor of biomedical engineering and neurological surgery at the University of Wisconsin-Madison.
"It cures -- hardens -- and it becomes a conductible electrode" that surrounds the nerve, Ludwig said.
Doctors then inject an outer sheath of insulation around the newly formed electrode, and use the same gel to craft a wire running from the injectrode to the surface of the skin.
"You now have a direct connection to stimulate a deep nerve from the surface of the skin, without affecting any nerves on the surface of the skin," Ludwig said. "We're trying to get this to the point where it's like getting a tattoo, in terms of invasiveness."
The use of electrical pulses to alter nerve activity, a technique called neuromodulation, has been shown to effectively treat chronic nerve pain, Ludwig said.
"When you feel pain, those nerves are sending an electrical signal that goes to your brain and tells you that you're feeling pain," Ludwig said. "This interrupts that signal."
However, neuromodulation hasn't been a viable means of treating nerve pain because it requires invasive and expensive surgery to place what amounts to a tiny, electrically charged computer inside a person, Ludwig said.
Because the neuromodulation procedure is so costly, patients often have to show that opioid drugs and other therapies aren't effective in treating their pain before insurance will cover the cost of an implant, Ludwig said. By then, the person may be addicted.
"If we can make this procedure less invasive, then you can start doing it not just for patients who have failed all drug therapies first. You can start doing it before the drugs or at least with the drugs," Ludwig said.
The research has been funded in part by the U.S. National Institutes of Health's Helping to End Addiction Long-term Initiative, launched in 2018 to find solutions to the opioid crisis in the United States.
In tests with pigs, Ludwig and his colleagues showed that injectrodes could effectively be implanted into the dorsal root ganglia on the spinal cord, "a target that's been shown to work well with pain," he said.
Researchers in the pig test used a $50 TENS, or transcutaneous electric nerve stimulation, unit from Walmart to provide electrical stimulation to the spinal cord of the swine, Ludwig said -- an example of how cheap this technology could prove.
The injectrodes also are softer and more flexible than metal implants, which researchers hope will help them better withstand the movements of the human body than today's implants.
Spinal cord stimulators have some of the worst safety records among all implants, causing more than 500 deaths and 80,000 injuries since 2008, according to a 2018 report by investigative journalists.
These implants malfunction and either shock or burn people in part because the devices and wires aren't able to stretch and flex with the human body. The injectrode gel is mechanically more akin to human tissue, which hopefully will make the injectable implants long-lasting and reliable, the study authors said.
The researchers are proceeding to human safety trials, which they hope to conclude by the end of 2021, Ludwig said.
Dr. Griffin Baum is an assistant professor of neurosurgery with Lenox Hill Hospital in New York City.
The injectrode technology being investigated "is another great step forward towards focused therapy for pain coming from the peripheral nervous system," Baum said, referring to nerves outside the brain and spinal cord.
"For those patients with chronic pain unexplained by a structural spine or anatomical problem, there are few promising therapies that can offer durable pain relief for many years and decades," Baum said. "This research and this type of electrode can not only help many patients in the short term but will hopefully provide the foundation for further research that can help to address the future tsunami of patients with chronic pain."
Neuromodulation is used to treat a number of other conditions besides pain, ranging from Parkinson's disease to depression, epilepsy and incontinence. "The hope is we can start hijacking the nervous system to treat a lot of different things," Ludwig said.
Obesity is one potential disease that might be treated through neuromodulation. Ludwig foresees using an injectrode "to actually hijack the signal from your stomach to your brain telling you that you're hungry."
A report on the pig injectrode study appears in the journal Advanced Healthcare Materials.
Harvard Medical School has more about neuromodulation to treat pain.
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