A Novel Silk Fibroin Conduit to Bridge a Nerve Gap Defect in a Rat Model

Amir Mahan Ghaznavi, MD, Lauren Kokai, BS, Sami Tuffaha, BS, Michael L. Lovett, PhD, David L. Kaplan, PhD, Kacey G. Marra, PhD

Introduction: Recently, a new silk fibroin microtube has been designed possessing qualities useful for peripheral nerve repair. Our aim was to examine its cellular inflammatory response and assess the functional recovery in rat sciatic nerve defect model. (1-5)

Methods: A randomized control study utilizing 40 Lewis rats was performed. Nerve guides (1 cm in length) composed of either silk or commercially available collagen type I were used to bridge an 8 mm defect in the sciatic nerve. An 8 mm autograft served as the positive control. After 1, 4 and 8 weeks, all samples were harvested. Macrophage recruitment was evaluated by the number of ED1+ cells. The thickness of the collagen capsule surrounding the graft or silk conduit was measured following Mason's Trichrome stain. Nerve regeneration was determined by using histomorphometric parameters as visualized through Toluidine Blue stain. Finally, muscle reinnervation was measured by the mass of the gastrocnemius muscle..

Results: The number of ED1+ cells was greatest 1 week post-operatively in both the autograft and silk conduit groups at the coaptation sites but disappeared following 8 weeks. Analysis of collagen formation revealed no significant differences in collagen thickness at all measured timepoints (p >.05), suggesting a similar foreign body response. Myelinated axons revealed a significant increase in fiber count by week 8 in the silk group as compared to the collagen indicating initial axon sprouts. The g-ratio for all groups after 8 weeks showed no significant difference between groups indicating the same level of neuronal maturity. Gastrocnemius weight ratio showed at week 8 the silk and collagen guides had no statistical difference, an indication of similar functional recovery following nerve repair.

Conclusion: Our study has shown a silk microtube can be used as a peripheral nerve conduit based on its favorable immunogenicity profile and substantial re-myelination capacity.

References:

1.  Lovett M, Cannizzaro C, Daheron L, Messmer B, Vunjak-Novakovic G, Kaplan DL. Silk fibroin microtubes for blood vessel engineering. Biomaterials. Dec; 28(35):5271-9 2007.

2.  Lovett ML, Cannizzaro CM, Vunjak-Novakovic G, Kaplan DL. Gel spinning of silk tubes for tissue engineering. Biomaterials. Dec; 29(35):4650-7 2008.

3.  Yang Y, Ding F, Wu J, Hu W, Liu W, Liu J, Gu X. Development and evaluation of silk fibroin-based nerve grafts used for peripheral nerve regeneration. Biomaterials Dec;28(36):5526-35 2007.

4.  Clavijo-Alvarez JA, Nguyen VT, Santiago LY, Doctor JS, Lee WP, Marra KG. Comparison of biodegradable conduits within aged rat sciatic nerve defects. Plastic Reconstructive Surgery. May;119(6):1839-51 2007.

5.  Li, S.T., S.J. Archibald, C. Krarup, and R. Madison. Peripheral nerve repair with collagen conduits. Clinical Materials 9: 195-200 1992.

Disclosure/Financial Support

Supported in part by the Armed Forces Research Institute of Medical Sciences and the National Science Foundation.

None of the authors has a financial interest in any of the products, devices, or drugs mentioned in this manuscript.