University of Pennsylvania School of Medicine researchers created a three-dimensional neural network -- a mini nervous system in culture -- that can be transplanted en masse, said Professor Douglas Smith, director of the school's Center for Brain Injury and Repair.

Smith's group placed neurons from rat dorsal root ganglia on nutrient-filled plastic plates. Axons sprouted from the neurons on each plate and connected with neurons on the other plate.

The plates were slowly pulled apart during several days, creating long tracts of living axons.

The cultures were embedded in a collagen matrix and implanted into a rat model of spinal cord injury. After four weeks the researchers found the geometry of the construct was maintained and the neurons at both ends and all the axons spanning the neurons survived transplantation.

More important, the researchers said, axons at the ends of the construct extended through the collagen barrier to connect with the host tissue as a sort of nervous tissue bridge.

The findings are reported in the Journal of Neurosurgery.