Implant could restore function to paralyzed and amputated limbs

(CN) — Although the physical connection to a limb is severed during amputation, the signals that originally guided those limbs still remain — signals that researchers say can be reconnected with a neural implant to restore functionality.

A team of researchers with the University of Cambridge developed an implantable device that integrates flexible electronics with stem cells to rewire the neural circuits between the brain and the severed nerves.

The biohybrid device overcomes the shortfalls of electronic-only implants, which are stymied by, according to a study published Wednesday in Science Advances, the “transplanted neurons struggle to reestablish functional connections in existing circuits without appropriate guidance. Similarly, electrodes cannot work without healthy working cells to interface, either because these cells are compromised by the injury or hidden by the formation of dense scar tissue around the implant.”

Dr. Damiano Barone, the study's co-author from Cambridge’s Department of Clinical Neurosciences, said that the team countered this interference by inserting a layer of muscle cells between the electronic apparatus and the living tissue.

“Rather than just placing a piece of the electronic technology on the tissue, we interfaced between the two with supplemental biological tissue, in this case, derived stem cells,” he said referring to induced pluripotent stem cells. Barone also said that this device is the first application of sutch stem cells in a living organism.

“By taking the nerve that is left after the amputation, because the information is still there, we implant into the big muscle of the shoulder or chest, we get the signals," he added.

Researchers first designed a thin flexible micro electrode array upon which they could grow a culture of induced pluripotent stem cells, which are derived from either skin or blood cells — rather than from embryonic sources — and can be propagated into all the different kinds of cells of the body. This biohybrid implant allows for a higher level of control between the implanted cells and the already existing neural circuitry.

According to Barone, the two separate elements of the device worked to enhance the other; the electronic component reduced interference from the body’s healing ability, while the muscle cells layer improved the function of the device itself, allowing for closer monitoring of the implanted organism and improved spatial resolution.

The study was conducted using the paralyzed limbs of rats. Researchers observed that while the rats did not have restored movement in the implanted paw, the device recorded electrical activity from the brain that indicated the neural connections were picked up. Throughout the 28 days of the study, the rats showed continual improvement with increased neural activity.

“What we proved is that the type of signals that we got from these devices is more than from any other device,” Barone said. “We asked the rats to perform consistent tasks, comparing the limbs that were normal to the limb that was paralyzed, but they still wanted to use it. We got a look at all the signals representing movement.”

Researchers also say that their device is designed to be minimally invasive compared to other developing methods of restoring function to paralyzed or amputated limbs, which are usually more complex and require patient-specification to brain activity. In contrast, the Cambridge biohybrid implant is more stable and more broadly applicable due to the use of induced pluripotent stem cells.

“What is possible now that was not possible a few years ago, is basically the stem cell technology. We can make the cells of our choice,” Barone said.

Although the technology is a long way from a human application, the researchers have made a huge first step toward the development of restorative bioelectronic therapies for amputees or others who have lost limb function.

“This interface could revolutionize the way we interact with technology," co-author Amy Rochford, from the Cambridge Department of Engineering, said in a statement. "By combining living human cells with bioelectronic materials, we’ve created a system that can communicate with the brain in a more natural and intuitive way, opening up new possibilities for prosthetics, brain-machine interfaces, and even enhancing cognitive abilities.”

The study and Barone noted that this technology may be useful in the future not only for restoring limb functionality but also in prosthetics and in those who have suffered brain injuries or strokes.

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