Bridging extra large defects of peripheral nerves: possibilities and limitations of alternative biological grafts from acellular muscle and Schwann cells.

Defects of peripheral nerves are bridged with autologous nerve grafts. Tissue-engineered nerve grafts offer a laboratory-based alternative to overcome limited donor nerve availability. Our objective was to evaluate whether a graft made from acellular muscle enriched with cultivated Schwann cells can bridge extra large gaps where conventional conduits usually fail. Our well-established rat sciatic nerve model was used with an increased gap length of 50 mm. The conduits consisted of freeze-thawed or chemically extracted homologous acellular rat rectus muscles and implanted Schwann cells. Autologous nerve grafts were used for control purposes. Biocompatibility of the grafts was demonstrated by Schwann cell settlement, revascularization, and macrophage recruitment. After 12 weeks regeneration was assessed clinically, histologically, and morphometrically. The control group showed superior results regarding axon counts, histologic appearance, and functional recovery compared with the muscle grafts. The chemically extracted conduits completely failed to support nerve regeneration. They were not stable enough to bridge longer nerve gaps with an expanded regeneration time. On the basis of morphological parameters freeze-thawed muscle grafts were, however, able to support peripheral nerve regeneration even over the extralong distance of 50 mm, and therefore are of potential benefit for new therapeutic strategies.