Alginate, a bioresorbable material derived from brown seaweed, enhances elongation of amputated axons of spinal cord in infant rats

Freeze-dried alginate sponge crosslinked with covalent bonds was developed in our laboratory and has been demonstrated to enhance peripheral nerve regeneration. In this study, we examined spinal cord repair using alginate sponge in infant rats. On postnatal day 8-12, the spinal cord was transversely resected at Th7-Th8 to produce a 2-mm gap. The gap was filled with alginate sponge in the alginate group. For the control group, the gap was left empty. In the alginate group, the recovery of evoked electromyogram and sensory-evoked potentials 6 weeks after surgery indicated that elongation of axons could establish electrophysiologically functional projections through the gap. A histological study revealed that myelinated and unmyelinated axons, surrounded by a perineurial-like structure, had elongated across the gap. An immunohistochemical examination revealed that elongation of astrocytic processes and/or migration of astrocytes into the alginate sponge was induced, whereas astrocyte gliosis was reduced at the interface between the implanted alginate and the host spinal cord, compared with the control group. However, a horseradish peroxidase tracing study revealed ascending and descending fibers had also elongated into the gap and reentered the other stump of the transected spinal cord beyond the gap. These results suggest that alginate might provide a permissive microenvironment for elongation of spinal cord axons.