Spider Silk Constructs Enhance Axonal Regeneration and Remyelination in Long Nerve Defects in Sheep

Abstract

BackgroundSurgical reapposition of peripheral nerve results in some axonal regeneration and functional recovery, but the clinical outcome in long distance nerve defects is disappointing and research continues to utilize further interventional approaches to optimize functional recovery. We describe the use of nerve constructs consisting of decellularized vein grafts filled with spider silk fibers as a guiding material to bridge a 6.0 cm tibial nerve defect in adult sheep.Methodology/Principal FindingsThe nerve constructs were compared to autologous nerve grafts. Regeneration was evaluated for clinical, electrophysiological and histological outcome. Electrophysiological recordings were obtained at 6 months and 10 months post surgery in each group. Ten months later, the nerves were removed and prepared for immunostaining, electrophysiological and electron microscopy. Immunostaining for sodium channel (NaV 1.6) was used to define nodes of Ranvier on regenerated axons in combination with anti-S100 and neurofilament. Anti-S100 was used to identify Schwann cells. Axons regenerated through the constructs and were myelinated indicating migration of Schwann cells into the constructs. Nodes of Ranvier between myelin segments were observed and identified by intense sodium channel (NaV 1.6) staining on the regenerated axons. There was no significant difference in electrophysiological results between control autologous experimental and construct implantation indicating that our construct are an effective alternative to autologous nerve transplantation.Conclusions/SignificanceThis study demonstrates that spider silk enhances Schwann cell migration, axonal regrowth and remyelination including electrophysiological recovery in a long-distance peripheral nerve gap model resulting in functional recovery. This improvement in nerve regeneration could have significant clinical implications for reconstructive nerve surgery.

Nerve guides manufactured from photocurable polymers to aid peripheral nerve repair

“…Synthetic NGC materials typically include polymers such as poly(lactic-co-glycolic acid) and their derivatives [8] and poly(caprolactone co-glycolic acid) [9]. The only naturally derived material used commercially to date is collagen [1], although spider silk is being investigated experimentally [10]), as are polymers produced by bacterial fermentation e.g. polyhydroxyalkoanates [11].…”

Olfactory-Ensheathing Cell Transplantation for Peripheral Nerve Repair: Update on Recent Developments

“…The challenge is to bridge larger nerve substance defects. In previous studies we utilized a novel artificial nerve graft (acellularized veins filled with spider silk) to bridge a long-distance 6-cm peripheral nerve defect in adult sheep [Radtke et al, 2011]. Regenerated axons within the graft were found 8 months after lesion induction and nerve repair.…”

Current progress and limitations of spider silk for biomedical applications

“…Two studies focusing on biofunctionality of spider silk did not notice any adverse effect because of an inflammatory response to implanted native spider silk. 71,72 In these two studies, dragline silk was used to construct peripheral nerve grafts by aligning the silk fibers in acellularized veins. In the first study, a 2-cm gap in the sciatic nerve in rats was experimentally induced and replaced by the spider silk nerve grafts.…”

“…The regenerated nerves also showed electrophysiological recovery and the animals regained a normal gait, strength, and coordinated movement of the limb. 72 The absence of observed inflammatory reactions could be explained by the long term duration of the implantation. No silk fibers could be identified at the time of sacrifice, which indicates that a possible inflammatory response may have subsided when the foreign material eventually was dissolved.…”

“…71 This study was followed by a similar study in sheep. 72 The investigators surgically removed 6 cm of the tibial nerve and replaced it either with a construct of spider silk fibers in acellularized veins or with autologous (from the same individual) nerve grafts. After 10 months, the tissue was histologically evaluated, which revealed axons regenerating through the constructs and the presence of myelinated axons indicating the migration of autologous Schwann cells.…”