By Pat Anson, PNN Editor
A team of scientists and engineers has developed a flexible electrode that can be injected into the body to stimulate damaged nerves, relieve chronic pain and treat other conditions.
The so-called “injectrode” could revolutionize neuromodulation therapy by eliminating the need for invasive spinal cord stimulators and other surgically implanted medical devices.
Researchers used a liquid silicone base -- similar to surgical glue – and mixed it with small metal particles to make it electrically conductive.
When injected around a nerve and allowed to cure, the injectrode performs much like a metal wire, but remains flexible.
Current neuromodulation treatments often rely on rigid implanted devices that can cost hundreds of thousands of dollars, require complex surgeries to install, and often fail or need to be replaced.
"Typical implants are really stiff, and so as the body moves, they wear and tear and break down. Our liquid cures, and the result is much closer to the normal elasticity of tissue. You can actually stretch it and increase its size 150 percent to 200 percent without losing its conductivity," says co-author Kip Ludwig, PhD, a professor of biomedical engineering and neurological surgery at University of Wisconsin-Madison.
“By virtue of its simplicity, the Injectrode has the potential to be less invasive, more robust, and more cost‐effective than traditional electrode designs, which could increase the adoption of neuromodulation therapies for existing and new indications.”
Ludwig and his colleagues reported their findings in the journal Advanced Healthcare Materials.
The injectrode has been tested on laboratory animals to stimulate their nervous systems. It was used in pigs to induce heart rate changes by stimulating the vagus nerve in the neck, an approach that's shown promise for treating heart failure, hypertension, lupus and cluster headaches.
"We essentially went through the standard repertoire of electrochemical tests to show this acts like a standard wire electrode that could be used to stimulate the nerve," says co-author James Trevathan, PhD, a postdoctoral fellow in Ludwig's lab.
Ludwig co-founded Neuronoff, a company based on the injectrode, with Case Western Reserve University biomedical engineering professor Andrew Shoffstall, PhD, and Neuronoff CEO Manfred Franke, PhD. Neuronoff recently secured a $2.1 million grant from the National Institutes of Health to further develop the injectrode to stimulate spinal nerves as a treatment for chronic back pain.
The researchers are testing a scheme in which they inject the fluid around the nerve, then extrude a thin insulated string of the material back to just underneath the surface of the skin, where they inject more of the composite material. Then they can use a basic transcutaneous electrical nerve stimulation (TENS) unit to stimulate the nerve from the surface of the skin.
"We're making a bypass from the surface of the skin to the location we want to stimulate," says Ludwig, who envisions using a robotic surgical system to install the injectrode in a procedure similar to getting a tattoo.
"As we learn more and more about how to interface with the nervous system, we're not limited to what we've implanted through an invasive surgical procedure. We can actually change how we stimulate, how we talk to the nerve, because we're essentially just routing our connection to this deep nerve back to the surface of the skin."
Spinal cord stimulators have some of the worst safety records among medical devices, according to a 2018 report by investigative journalists. Stimulators are often touted as safer alternatives to opioid pain medication, but a review of FDA data found over 500 deaths and 80,000 injuries involving stimulators since 2008. Patients reported being shocked or burned by the devices and many had them removed.