Every year, hundreds of thousands of people suffer from paralyzed limbs as a result of peripheral nerve injury. Recently, implantation of artificial nerve grafts has become the method of choice for repairing damaged peripheral nerves. Grafts can lead to some degree of functional recovery when a short segment of nerve is damaged. But they are of little use when it comes to regenerating nerves over distances greater than a few millimeters, and such injuries therefore often lead to permanent paralysis.
Now though, surgeons from Germany have made what could be a significant advance in nerve tissue engineering. They have developed artificial nerve grafts made from hollowed-out pig veins filled with spider silk fibres and, in a series of animal experiments, showed that the grafts can enhance the regeneration of peripheral nerves over distances of up to 6cm. Their findings have just been published in the open access journal PLoS One.
Merged series of phase contrast micrographs showing neurite outgrowth in rat dorsal root ganglion cells grown on an acetylcholine biopolymer. (Christiane Gumera)
Last year, Yadong Wang and his colleagues at the Georgia Institute of Technology reported that they had produced a dopamine biopolymer that promotes the growth of neurites in PC12 cells.
Now, the team have taken that work one step further, with the finding that another similar polymer has the same effect on nerve cells. When Wang and Ph.D. student Christiane Gumera cultured the cells on an acetylcholine polymer substrate, the severed processes regrew at a similar rate to those grown on other substrates that are known to promote regeneration.
The processes were also found to express the synaptic vesicle protein synaptophysin. The presence of this protein is significant, as it indicates that the regenerated processes contain at least some of the proteins that are required for recovery of function.
The mammalian nervous system is known to have a limited regenerative capacity, and there are many factors known to promote regeneration of nerve cell processes in the culture dish. However, researchers have so far had little luck with regenerating the severed nerves of live animals.
One major obstacle is believed to be the scar tissue that forms at an injury site. Wang and Gumera are now planning to produce polymer scaffolds to bridge the gaps between the ends of animals’ severed nerves. If the scaffolds cannot induce nerves to regenerate throught the scar tissue, they might prove useful in stimulating the formation of new nerve cells.
Gumera, C. B. & Wang, Y. (2007). Modulating Neuronal Responses by Controlled Integration of Acetylcholine-like Functionalities in Biomimetic Polymers. Adv. Mater. DOI: 10.1002/adma.200790097.