Self-assembling fibers help nerve repair

By CHARLES CHOI, United Press International  |  Jan. 23, 2004 at 9:00 AM
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NEW YORK, Jan. 23 (UPI) -- New, self-assembling, biodegradable scaffolds could help repair and regrow damaged nerve cells, possibly bringing new hope to victims of paralysis, scientists told United Press International.

"This helps raise the possibility of helping the spinal cord regenerate, a possibility we are literally studying at this moment," said researcher John Kessler, a neurologist at Northwestern University in Evanston, Ill.

The new technique involves using tiny, artificial, 3-D scaffolds that can store or attract cells. The scaffolds give neurons or nerve cells a framework on which to rebuild. The materials typically are biodegradable -- they dissolve as cells multiply to fill their place.

Northwestern materials scientist Sam Stupp and colleagues developed organic molecules that can assemble themselves in seconds into transparent scaffolds made of fibers only 5 to 8 nanometers -- billionths of a meter -- long. Using the nano-scaffolds, doctors can create templates for nerve regeneration simply by injecting ingredients into the body, instead of having to cut a person open to surgically implant a scaffold.

"That's the real advance here," Kessler said.

Kessler began researching spinal cord injury after his daughter was paralyzed in a skiing accident.

"It's not going to by itself regenerate all problems in the nervous system," Kessler cautioned. "I do think it's a very big step -- but it's just one step."

The investigators experimented with neural progenitor cells from mice. These cells are the primordial material that more complicated nerve cells found in the brain and spinal cord emerge from, a process known as differentiation.

The research team took the building blocks for the scaffolds and incorporated an amino acid sequence into them known to help promote the growth of neurites, the branches extending from nerves that help the cells talk with one another. "Think of them as wiring," Kessler explained.

Anchoring the amino acid sequences to the fibers is crucial, Kessler said. If the growth promoters are injected into the scaffold after it is formed, they could be broken down before cells can use them, or not coat cells evenly. The fact the fibers are so tiny means they can be tightly packed together, to surround cells with as much of the growth promoting amino acid sequence as possible. The scaffold does not assemble until its ingredients make contact with ions, such as the electrically charged molecules on the surrounding cells.

Electron microscope images revealed the progenitor cells rapidly differentiated into neurons. Moreover, they grew without any of the inhibitions limiting regeneration in the body.

"The problem with regeneration of the central nervous system -- the brain and spinal cord -- is that the materials surrounding the cells do not allow them to regenerate," Kessler explained. For instance, damaged nerve cells develop what is called a glial scar around them.

"One of the exciting things here is the scaffold unexpectedly was found to block neural progenitor cell differentiation into astrocytes, the cells that make up the glial scar," Kessler said.

The researchers now are experimenting with Stupp's fibers on lab mice and rats to see if they can help regenerate from spinal cord damage and stroke. They also are investigating why the scaffolds inhibit differentiation.

"This is the first major hopeful development in the direction of nerve regeneration and repair," National Science Foundation's polymer program director Andy Lovinger told UPI.

Kessler added it might be possible to tailor the nanofibers with chemicals targeting other kinds of cells.

"The ramifications of this work certainly far exceed what can happen in the nervous system. There's every reason to believe it can help regenerate other organ systems, providing the environment for what you can in essence think of as an artificial pancreas, or for bone formation, and on an on," he noted.

Kessler said there is commercial interest in this work, but added, "Both Dr. Stupp's and my primary concern is not the financial impact, but its impact on patients."


Charles Choi covers research for UPI Science News. E-mail

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