Spatial-temporal progress of peripheral nerve regeneration within a silicone chamber: parameters for a bioassay.

The spatial-temporal progress of peripheral nerve regeneration across a 10-mm gap within a silicone chamber was examined with the light and electron microscope at 2-mm intervals. A coaxial, fibrin matrix was observed at 1 week with a proximal-distal narrowing that extended beyond the midpoint of the chamber. At 2 weeks, Schwann cells, fibroblasts, and endothelial cells had migrated into the matrix from both nerve stumps. There was a delay of 7-14 days after nerve transection and chamber implantation before regenerating axons appeared in the chamber. At 2 weeks, nonmyelinated axons were seen only in the proximal 1-5 mm of the chamber in association with Schwann cells. Axons reached the distal stump by 3 weeks and a proximal-distal gradient of myelination was observed. These observations define the parameters of a morphologic assay for regeneration in this chamber model which can be used to investigate cellular and molecular mechanisms underlying the success of peripheral nerve regeneration.