Nature
23 January 2004
http://www.nature.co.../040119-13.html
HELEN R. PILCHER
Miniature scaffolds give nerves something to grow on.
© Digital Vision
It may well be the smallest scaffolding in the world, and the easiest to set up. Researchers have devised a tiny self-assembling structure that they hope will help repair damaged spinal cords.
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.
Samuel Stupp and colleagues from Northwestern University, Chicago have now found a way to build a bridge out of liquid instead1.
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.
Self-assembly
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 team also laced each molecule in the liquid with a tiny protein fragment that nerve cells can recognize and latch on to. This may aid the development and growth of nerve cells, speculates Stupp.
It's a sophisticated system, says David Mooney, who studies tissue engineering at the University of Michigan. It allows you to control the physical and biological make-up of the structure.
Bridging the gap
But there are many hurdles to overcome. Even with the chemically laced scaffolding in place, nerve cells may still struggle to regrow.
After a spinal-cord injury, the surrounding cells multiply to form a dense scar, explains spinal-cord researcher Elizabeth Bradbury from Kings College London. This barrier is impenetrable to nerve cells, so enzymes that can break it down may also need to be added, she says.
To give spinal-cord repair an extra boost, the team also tried introducing fresh nerve cells into the system. When they added stem cells - cells that can turn into other, specific types of cells, such as nerves - to the scaffolding solution, they turned into neurons and began to grow within the solidified bridge. The team plans to try to do the same thing in damaged rodent spinal cords.
References
Silva, G. A. et al. Selective differentiation of neural progenitor cells by high-epitope density nanofibers. Sciencexpress, www.sciencexpress.org (2004). |Homepage|
