Nanofibers Heal Spinal Cords

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Nanofibers help nerves: Northwestern University researchers have designed molecules made of biological parts, such as amino acids and fats, that self-assemble into cylindrical nanofibers. The researchers inject a solution of the molecules into the injured spinal cords of mice, where the nanofibers promote the growth of nerve fibers. Credit: Samuel Stupp, Northwestern University

Stupp and his colleagues have found other uses for the self-assembling molecules in the past. They have designed molecules with slightly different chemistries that promote the growth of blood vessels and that align themselves to mimic bone structure. In a 2004 Science paper, the researchers reported that in a lab culture of brain cells, versions of the material encourage the cells to grow the nerve fibers that extend into the spinal cord. They also found that the material prevents cultured nerve stem cells from growing into scar tissue.

The new work is the first test for the material to heal spinal cord injuries in animals. And Kessler says that it worked better than the researchers expected. The researchers stimulated a spinal cord injury in mice and injected the material 24 hours later. They found that the material reduced the size of scars and stimulated the growth of the nerve fibers through the scars. It promoted the growth of both types of nerve fibers that make up the spinal cord: motor fibers that carry signals from the brain to the limbs, and sensory fibers that carry sense signals to the brain. What is more, the material encouraged the nerve stem cells to mature into cells that create myelin--an insulating layer around nerve fibers that helps them to conduct signals more effectively.

Nine weeks after the injections, the mice that had been treated showed improvements over untreated mice. The animals could support their body weight on their hind legs and lift their lower bodies. "Animals that couldn't use hind legs at all now had improved ability to use their hind legs," Kessler says. "It was certainly not a cure but quite a substantial improvement in function. They're able to navigate around their cages."

Stupp has cofounded a Stokie, IL-based company called Nanotope, which is working on developing the self-assembling nanofiber therapy for human beings. The first step would be making a material that meets Food and Drug Administration standards and then testing it in clinical trials. So far, Kessler says, some basic tests of the material on human cell cultures have so far shown no apparent toxic effects.