Bridging defects in nerve continuity: influence of variations in synthetic fiber composition

Synthetic filaments introduced into a silicone tube may help to enhance axonal growth over extended defects in nerve continuity [1]. Here we test the influence of number (0, 3, 7 or 15), size (diameter 150 or 250 microm) and material of filaments (polyamide or catgut) enclosed in such tubes (inner diameter 1.98 mm) on axonal growth across a 10 mm defect in rat sciatic nerve. The morphology of the tube content was analyzed four weeks post-surgery. The area of the formed tissue matrix inside the tube showed no difference between the groups. Myelinated axons were observed in the formed tissue matrix inbetween and peripheral to the filaments, however, separated from the filaments by concentric cell layers. The number of myelinated axons was less in the tubes with 15 filaments, most pronounced when catgut filaments were used. In most cases, except in tubes with 15 catgut filaments, fibers had grown into the distal nerve segment (pinch reflex test/light microscopy). We conclude that an intrinsic framework consisting of a limited number of synthetic filaments inside an extrinsic framework (silicone tube) does not disturb nerve regeneration. The formed tissue matrix was neither influenced by the presence or the numbers (if less than or equal to seven filaments), type of filaments nor the size of the filaments indicating the importance of the inserted nerve segments.