Rats whose spinal cords had been cut walked somewhat better eight weeks after a plastic tube filled with chemicals that promote nerve growth was implanted in their spine. “We know the rats improved. What we have to do now is figure out how significant the improvement is,” said lead researcher Molly Shoichet, Ph.D., an associate professor at the University of Toronto. Shoichet, who has studied 80 rats to date, cautions that significantly more work needs to be done with animals before the treatment can be tested in people.
On a common test of paralysis that is scored from 1 (complete paralysis) to 21 (normal movement), injured and untreated rats scored a 2. Those rats that were treated with the chemical-filled tube scored between 8 and 11, depending on the chemical used.
The tube, made of the same material used for contact lenses and only 5 millimeters in length, fits snugly around the injured area and serves as a “bridge” that connects the damaged nerves. Designed to mimic the flexibility of the spinal cord, the tube provides a pathway along which neurons can grow.
“We saw some directed nerve tissue growth along the plastic tube, but we do not yet know if the severed nerves were connected to the newly grown tissue,” said Shoichet. “We hope that once axons grow across the gap they will make the appropriate connections.”
Unlike nerves in other parts of the body which regenerate rapidly after an injury, spinal cord nerves must be coaxed into growing. Other researchers are testing the practicality of using injections or genetically-modified cells to deliver growth factors to the injured neurons, but Shoichet’s group is the first to use a chemical-filled tube that matches the properties of the spinal cord itself.
There are few effective treatments for spinal cord injuries. In the 1940s, most injuries were fatal. Today, improvements in emergency medicine mean more people survive the initial injury, and most naturally regain some function within six months, according to the National Institute of Neurological Diseases and Stroke (NINDS). Physical therapy helps to maintain flexibility and function of the muscles and joints, but most sufferers are still left with permanent, severe disabilities. NINDS estimates that 10,000 people suffer a spinal cord injury every year, and 200,000 are currently living with the injury.
As recently as a decade ago, doctors’ only option was to realign and then immobilize the spinal column. Methylprednisolone — the first and only drug proven to limit secondary damage to the nerves — was therefore revolutionary when it was approved in 1990. But there is still no standard treatment to reverse the damage.
The poster on this research, MACR 29, will be presented at 4:15 p.m., Tuesday, August 28, at McCormick Place South, Room S105B/C, during the symposium, “Polymers in Biomedical Applications.”
Molly Shoichet is an associate professor in the department of chemical engineering and applied chemistry at the University of Toronto.
— by Tamara Schneider
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