A novel matrix of neural stem cells and a biodegradable polymer can quickly repair brain damage from stroke in rats. Within just seven days of injecting the concoction directly into the damaged part of the brain, new nerve tissue grew to fill stroke-induced cavities.

Scientists say that the key to the advance, published today in the journal Biomaterials, is the use of a biodegradable polymer called PLGA, which ensures that the stem cells remain in the area of stroke damage and establish connections with surrounding brain tissue. By reducing the number of stray stem cells, the system is likely to be safer as well as more effective than other methods, the researchers add.

Strokes, which occur due to bleeds or blocked blood vessels in the brain, cause some brain tissue to die. This dead tissue is then removed by the immune system, leaving a hole. "We would expect to see a much better improvement in the outcome after a stroke if we can fully replace the lost brain tissue, and that is what we have been able to do with our technique," says Mike Modo, a neurobiologist at the Institute of Psychiatry at King's College London, who oversaw the research.

Earlier studies had indicated that using support structures, including carbon nanotubes, might help stem cells that were introduced to replace the brain tissue damaged by a stroke. But the latest research, sponsored by the Biotechnology and Biological Sciences Research Council, appears to take the process a significant step farther. The team was able to show that the hole in the brains of rats caused by a stroke was completely filled with "primitive" new nerve tissue within seven days. This raises the possibility of radically better treatments for a condition that is the leading cause of adult disability in industrialized countries.

The researchers injected particles of the PLGA polymer loaded with neural stem cells directly into the stroke cavities. Once inside the brain, the particles link up to form complex scaffolds. Modo's team used MRI scans to pinpoint where the stem-cell injections were needed and to monitor the development of new brain tissue. "Over a few days we can see cells migrating along the scaffold particles and forming a primitive brain tissue that interacts with the host brain," says Modo. "Gradually, the particles biodegrade, leaving more gaps and conduits for tissue, fibers, and blood vessels to move into." The next step, he says, will be to add the growth factor VEGF, which should encourage blood vessels to enter the new tissue and speed its development into mature tissue.