One of the biggest challenges facing next-generation electrode implants – think cochlear implants that have revolutionized the approach to restoring hearing – is that there is often a “mechanical mismatch” between soft tissues and stiff implants. The resulting stress can cause inflammation and even outright rejection by one’s body, rendering even the most sophisticated implants useless.
Now a multidisciplinary team headquartered in Switzerland that includes experts in materials science, electronics, neuroscience, medicine, and computer programming is moving toward clinical trials of what it calls e-Dura, short for “electronic dura mater,” which mimics both the shape and elasticity of dura mater, the protective membrane of both the brain and spinal cord.
In a study published last week in Science, they reported that their soft, flexible implant, which is embedded with electrodes, interconnects, and chemotrodes that can handle millions of cycles of mechanical stress, chemical injections, and electrical stimulation pulses, is working so well in lab rats it’s allowing them to walk again even after paralyzing spinal cord injuries.
The stretchy, electronic dura mater not only avoided triggering an immune response, which often results in inflammation, it also more closely mimicked the rats’ natural movements.
“Our e-Dura implant can remain for a long period of time on the spinal cord or the cortex precisely because it has the same mechanical properties as the dura mater itself,” study co-author and neuroprosthetics expert Stéphanie Lacour said in a press release. “This opens up new therapeutic possibilities for patients suffering from neurological trauma or disorders, particularly individuals who have become paralyzed following spinal cord injury.”
Beyond better integrating with the flexible tissue itself, e-Dura is also capable of delivering electrical impulses and chemicals, and even monitoring electrical signals from the brain in real time. This allowed the researchers to see where the rats intended to go before they even moved.
Not only did it work in this round of animal testing, it did so for two months – a long time in a rat’s life. Dr. Catharine Paddock wrote in Medical News Today that traditional, rigid implants “would have caused significant nerve tissue damage during this period of time.”
When Dr. Jamie Williams, a biomechanical and medical device expert, demonstrates the “viscoelasticity” of biological materials like the dura mater, which she is called to do both as an expert witness in court and a professor, she likes to bring silly putty, she told me.
“If you take it in either hand and quickly pull your hands apart, you can actually get it to fracture,” she said. “If you take it in either hand and slowly pull your hands apart, you will actually get it to stretch and deform. The reason is that you’re giving the material time to absorb the energy and deform when you apply it more slowly as opposed to a quick application of the load. Our soft tissues are no different.”
Williams added that there is currently litigation of an entire genre of medical products designed to address urinary incontinence and pelvic organ prolapse. Medical device companies have been implanting mesh material to address these issues, but they’re failing as a whole, and Williams said this is largely because the material properties are inadequately matched.
“When my boys are crawling around on their jeans, they wear out the knees of their jeans; you’ve got a flexible surface rubbing between two rigid structures – their bony knees and the floor,” she explained. “The physiological response to what the body perceives to be a trauma is inflammation. Right now we don’t really have a device that is the gold standard. We’ve made multiple attempts, but nothing has been successful because of these limitations.”
Other attempts to rethink these kinds of implants also involve resolving this problem of mechanical mismatch. Just last year, one paralyzed man from Poland was able to recover some mobility and sensations in his legs after surgeons bridged his injury so that nerve cells, which were led on by a nose cell called an “olfactory ensheathing cell,” could regrow across the scar tissue.
The e-Dura approach still requires implanting foreign, electronic material onto one’s spine or brain, so some amount of inflammation is likely to occur. But as obvious as the solution sounds, it actually presents a novel approach to brain and spinal implants that could ultimately have implications for a wide range of patients, including those with spinal cord injuries, Parkinson’s, epilepsy, chronic pain, and Tourette Syndrome.
This does, however, mean that even given successful clinical trials, which the Swiss team hopes to launch as early as June, we’re likely still years away from FDA approval in the US, Williams cautioned.
“We have a long way to go, but I see this as being a great next step. As scientists we build upon each other, so if they have some success these concepts will then trickle here and will definitely prompt or promote other researchers following similar paths and continue with the ongoing evolution of medical devices. So I think this is a good thing for us all the way around.”