gms | German Medical Science

Objectives: Metallic magnesium (Mg)is a promising bioresorbable implantation studies have suggested that linear biomaterials could enhance repair. We tested the hypothesis that bioresorbable metallic magnesium (Mg) filaments would provide structural support and a supportive environment to improve axonal regeneration in short nerve gaps in adult rat sciatic nerves.

Method: 21 adult female Lewis rats underwent sciatic nerve transection. Poly(caprolactone) (PCL) nerve conduits filled with normal saline were used to reconstruct short (6 mm) gaps. The experimental groups (n=7 rats/group) were: 1) Saline only 2) conduit plus a 250 micron Titanium (Ti) filament and 3) conduit plus a 250 micron Mg filament. The sciatic nerves were harvested 6 weeks later with 2-5 mm of distal and proximal nerve stumps, analyzed with MicroCT and embedded in paraffin. Paraffin embedded tissues were sectioned (10 µm thick) and were stained with hematoxylin & eosin or Masson's Trichrome. Immunostaining was performed for NF200 (axons), ED1 (macrophages), and Glut-1 (perineurium).

Results: MicroCT imaging demonstrated that Mg filaments were partially resorbed at the 6 week time point. In the distal nerve stumps, axonal content was improved with Mg filaments compared to empty conduits or conduits containing Ti filaments, which did not degrade over time. Immunostaining demonstrated that, while fascicle size (via Glut-1) was not statistically different between the 3 groups, Mg filaments increased the size of regenerating axons in the distal stump (0.81 micron2) compared to control saline conduits (0.46 micron2) and Ti conduits (0.34 micron2) (P<0.05). Additionally the percentage of new tissue with filled with regenerating axons was increased in the Mg group (3.1%) compared to the Ti (1.2%) and saline conduit groups (1.1%) (P<0.05). Although 1 animal demonstrated microbubbles surrounding the Mg filament, macrophage staining revealed minimal inflammatory response surrounding the filaments.

Conclusion: Mg microfilaments improved axonal outgrowth in PCL conduits compared to those containing a Ti metal filament or normal saline. The regenerating axons appeared to cluster around the resorbed Mg filaments indicating that this acts as an early physical support. Subsequently, the released Mg had a significant effect on the total amount of axonal material growing across this relatively short nerve injury gap at this relatively early time point, which supports the idea that the Mg presence aided this early measure of nerve regeneration.