Roland Piquepaille's Technology Trends
How new technologies are modifying our way of life

samedi 24 janvier 2004

Scientists at Northwestern University have designed the smallest scaffoldings in the world made of self-assembling structures built from synthetic molecules. This news release says that these nanostructures can promote neuron growth. This could lead to "the reversal of paralysis due to spinal cord injury."

"We have created new materials that because of their chemical structure interact with cells of the central nervous system in ways that may help prevent the formation of the scar that is often linked to paralysis after spinal cord injury," said Professor Samuel Stupp.
Similar to earlier experiments that promoted bone growth, the scientists now have successfully grown nerve cells using an artificial three-dimensional network of nanofibers, an important technique in regenerative medicine.
"We have shown that our scaffold selectively and rapidly directs cell differentiation, driving neural progenitor cells to become neurons and not astrocytes," said Stupp, who led the research team in Evanston. "Astrocytes are a major problem in spinal cord injury because they lead to scarring and act as a barrier to neuron repair."

In "Self-assembling scaffold for spinal-cord repair," Nature adds more details on how the process works.

Every year in the United States alone, about 15,000 people damage their spines. Few recover fully as it is difficult for damaged nerves to grow across the gap in a severed spinal cord.
Researchers have tried to build bridges across these gaps, so that nerves can grow. Most of these are made out of a solid material such as collagen, but require invasive surgery that can cause extra trauma to the injury.

So why not use a liquid instead?

When the solution is injected into a damaged rodent spinal cord, it turns into a gel-like solid, says Stupp. The scaffold is designed to disintegrate after four to six weeks, hopefully leaving healthy spinal cord behind.

Nature also how the synthetic molecules are self-assembling into nanostructures.

The liquid is made up of negatively charged molecules. Normally, they repel one another and keep the substance in liquid form. But when the fluid encounters positively charged molecules - such as the calcium or sodium ions found in living tissue - they clump together. "The effect happens almost instantly," says Stupp.
The molecules are designed to aggregate in a particular way, forming a mass of tiny, hollow tubes. Each tube is about 5 nanometres wide -- 10,000 times smaller than the width of a human hair -- and several hundreds of nanometres long. The structure is porous, allowing nerve cells to grow through and around it.

The journal Science published the results of this research work, under the name "Selective Differentiation of Neural Progenitor Cells by High-Epitope Density Nanofibers." Here is the abstract (free registration needed).

Neural progenitor cells were encapsulated in vitro within a three-dimensional network of nanofibers formed by self-assembly of peptide amphiphile molecules. The self-assembly is triggered by mixing cell suspensions in media with dilute aqueous solutions of the molecules, and cells survive the growth of the nanofibers around them. These nanofibers were designed to present to cells the neurite-promoting laminin epitope IKVAV at nearly van der Waals density. Relative to laminin or soluble peptide, the artificial nanofiber scaffold induced very rapid differentiation of cells into neurons, while discouraging the development of astrocytes. This rapid selective differentiation is linked to the amplification of bioactive epitope presentation to cells by the nanofibers.

If you want even more information, but in plain English, you also can read "Injectable scaffold aids rebuilding of nerves," published by the New Scientist.

Sources: Megan Fellman, Northwestern University, January 22, 2004, via EurekAlert!; Helen R. Pilcher, Nature, January 22, 2004; Science Magazine, January 22, 2004; Laura Spinney, New Scientist, January 22, 2004

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