Self assembling nanofibers heal spinal cords

Nano fix: An electron-microscope image shows the matrix of cylindrical nanofibers that self-assemble from engineered biological molecules in a solution. Credit: Journal of Neuroscience

An engineered material that can be injected into damaged spinal cords could help prevent scars and encourage damaged nerve fibers to grow. The liquid material, developed by Northwestern University materials science professor Samuel Stupp, contains molecules that self-assemble into nanofibers, which act as a scaffold on which nerve fibers grow.

Stupp and his colleagues described in a recent paper in the Journal of Neuroscience that treatment with the material restores function to the hind legs of paralyzed mice. Previously, researchers have restored function in the paralyzed hind legs of mice, but those experiments involved surgically implanting various types of material, while the new substance can simply be injected into the animals. The nanofibers break down into nutrients in three to eight weeks, says Stupp.

Right now, there is no cure for the thousands of people who have injuries to the spinal cord, the bundle of long nerve fibers that connect the brain to the limbs and organs of the body. When it is damaged, nerve stem cells form a scar at the point of the injury, which blocks nerve fibers and keeps them from growing, says John Kessler, professor of stem cell biology at Northwestern's Feinberg School of Medicine, who collaborated on the work with Stupp. Nerves can no longer carry signals to and from the brain, causing patients to lose sensation, digestion, and movement. "It is like cutting a telephone cable," Kessler says. "We're thinking of regrowing the nerve fibers and rewiring the cut."

Other researchers have tried to regenerate nerve fibers using various approaches. They have used natural materials such as collagen as well as synthetic biodegradable polymers to make scaffolds that support nerves, helping them to grow. Implanting these materials at the injury requires surgery.

The new material is different because the researchers can inject it as a liquid directly into the spinal cord. Negatively charged molecules in the liquid start clumping together when they come in contact with positively charged particles such as calcium and sodium ions in the body. The molecules self-assemble into hollow, cylindrical nanofibers, which form a scaffold that can trap cells. On the surface of the nanofibers are biological molecules that inhibit scars and encourage nerve fibers to grow. "The idea of using self-assembling nanofibers that can be directly injected into the spinal cord is appealing," says Harvard Medical School professor Yang Teng, who does neural stem cell research for spinal cord injuries.

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