Sending signals: Prof creates ‘mini-nervous system’
Doug Smith’s goal is simple: He wants to help the human brain talk to the human body—even after catastrophic injury.
Smith, a professor in the department of neurosurgery and director of Penn’s Center for Brain Injury and Repair, is at the cutting edge of his field, with work that has hinted at the possibility of creating a brain-machine interface that would allow the brain to “talk,” in a real and significant way, with an artificial limb, or, more recently, repairing damaged nerve systems with transplant material grown in a lab setting, then transplanted successfully in rats.
Smith’s work offers hope for an untold number of patients—those who have lost limbs or limb function due to massive injury, those who have suffered spinal cord injuries, and many others.
“The goal here is to recreate the signals [from the brain],” Smith says.
Smith’s most recent work focuses specifically on nerves—the systems that carry sensory information to and from the brain from all parts of our bodies—and how to repair them after they’ve been damaged.
Last month, Smith and his team reported in the Journal of Neurosurgery that they had created a three-dimensional “mini-nervous system” in their lab, then successfully transplanted the living material in rats. In the study, the team placed neurons from near the spinal cords of rats on nutrient-filled plastic plates, then waited until axons (pictured)—the projections of nerve cells that carry electric impulses away from the cell—grew on the nerve cells on each plate. The team connected the two sets of nerve cells and then slowly pulled them apart, creating long sets of living axons that could then be implanted in the rats. The team achieved that by applying mechanical tension to each plate. The tension helped the axons grow at a rate of about 1 mm per day.
“With birth trauma, surgery, gunshot wounds and other accidents, very major nerves are cut in half—you lose entire segments of them,” Smith explains. “But you can’t just yank on nerves and put them back together. … But we’ve found that we can grow this material, embed it in collagen, bring it out, [transplant it] and that even four months later, it is still surviving. An electrical signal can be passed through and we see some functional recovery.”
Now the team wants to do the same thing with human tissue. They plan to use human dorsal root ganglia neurons, which are more likely to survive in culture, to create a human version of the transplantable axons. Smith notes that while the rat experiment was promising, there are still questions about how well the technique may translate to humans. That’s partially because rats are so unusually resilient to injury.
Even still, Smith’s goal remains to eventually create a method that would help people who have lost nerve function due to massive injury regain some feeling and control of their limbs. Currently, there are no treatments available that are capable of doing what Smith’s technique may one day deliver.
“Of course everyone wants to help animals,” Smith said, “but we really want to apply this to humans.”
This most recent work is similar to Smith’s other recent research, which involves the creation of a brain-machine interface that could one day offer new life for patients with artificial limbs. In this work, Smith has shown the potential to create a system, once again using axons, to better communicate between the brain and an artificial device. Because this method uses real human tissue, it is less invasive than techniques that rely on the implantation of a device in brain tissue. Just as important, the quality and quantity of brain signals sent and received via these tissues creates more “real” sensory and motor input and outputs than can be provided by artificial devices.
“With this technique, you could actually sense where your arm is and what it’s doing,” Smith says. “Right now, the prosthetic devices we have can do quite impressive things, but they are limited.”
For more information on Penn’s Center for Brain Injury and Repair, visit www.med.upenn.edu/cbir/index.shtml.
Originally published March 27, 2008
