Long-term survival and outgrowth of mechanically engineered nervous tissue constructs implanted into spinal cord lesions.

While most approaches to repair spinal cord injury (SCI) rely on promoting axon outgrowth, the extensive distance that axons would have to grow to bridge SCI lesions remains an enormous challenge. In this study, we used a new tissue-engineering technique to create long nervous tissue constructs spanned by living axon tracts to repair long SCI lesions. Exploiting the newfound process of extreme axon stretch growth, integrated axon tracts from dorsal root ganglia (DRG) neurons were mechanically elongated in vitro to 10 mm over 7 days and encased in a collagen hydrogel to form a nervous tissue construct. In addition, a modified lateral hemisection SCI model in the rat was developed to create a 1 cm long cavity in the spinal cord. Ten days following SCI, constructs were transplanted into the lesion and the animals were euthanized 4 weeks post-transplantation for histological analyses. Through cell tracking methods and immunohistochemistry, the transplanted elongated cultures were consistently found to survive 4 weeks in the injured spinal cord. In addition, DRG axons were observed extending out of the transplanted construct into the host spinal cord tissue. These results demonstrate the promise of nervous tissue constructs consisting of stretch-grown axons to bridge even extensive spinal cord lesions.