Poly lactic acid-caprolactone copolymer tube with a denatured skeletal muscle segment inside as a guide for peripheral nerve regeneration: A morphological and electrophysiological evaluation of the regenerated nerves

A biodegradable copolymer of poly L-lactic acid and ε-caprolactone (PLAC) was manufactured into a tube, in which a denatured skeletal muscle segment was placed longitudinally. This model tube was implanted as a guide to promote nerve regeneration across a 5 cm gap in the rabbit sciatic nerve. Five months after implantation, good nerve regeneration was found throughout the graft and in the distal host nerve. The population (29.6/16 x 10^p2 μm^p2) of regenerated nerves in the graft was higher than that of the contralateral normal sciatic nerve (18.0/16 x 10^p2 μm^p2). Regenerated nerve fibers extended to the distal host nerve. The number of myelinated fibers was 13.7/16 x 10^p2 μm^p2 at a level 1.5 cm from the distal suture. The diameters (below 2 μm) of most regenerated myelinated nerves in the graft and in the distal host nerve were much smaller than those (6-8 μm) of normal nerves. Electrophysiological evaluation showed that the hindlimb muscle (gastrocnemius) was innervated by motor nerves in all animals 5 months after implantation. These results indicate that the PLAC tube with a denatured muscle segment inside provided good conditions for nerve fiber regrowth. The PLAC tube is thought to protect the denatured muscle segment from rapid dissociation in the host tissue.