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Nerve guide conduits were originally developed as an alternative to classic microsurgical repair to prevent axonal escape from the suture line and to reduce operative site pain.
However, over the past two decades, development and clinical application of nerve guides has emerged as a promising alternative1 to autografts for nerve deficit repairs. Compared to autografts, the use of nerve guides has been demonstrated to eliminate the risk of donor site morbidity5 and reduce the potential for neuroma pain.
One such nerve guide is NeuraGen® 3D Nerve Guide Matrix, which features an inner type 1 collagen matrix infused with chondroitin-6-sulfate (collagen-GAG) that is designed to mimic Schwann cell basal lamina, making it a “biologically rational substrate” for nerve repair.3
Learn what makes the composition of NeuraGen 3D unique and what this could mean for the potential of this type of conduit to support the important role that Schwann cells play in nerve regeneration.
Research on the Function of Schwann Cells
Schwann cells support axon outgrowth and myelination during peripheral nerve repair.3 During nerve regeneration after injury, they direct axonal regeneration by presenting growth factors to the regenerating axonal growth cones.3 The success of an artificial nerve graft is dependent on the initial effective migration and colonization by Schwann cells. Otherwise, or abortive axonal regeneration3 could occur.
For years, much of the research on peripheral nerve regeneration and collagen-based nerve conduit design had been focused on axons. Yet a 1994 study4 by Rodger Madison and Simon Archibald, PhD Chief Scientist at Integra LifeSciences, demonstrated that Schwann cells were responsible for the entire orchestration of the peripheral nerve trunk reconstruction within a nerve guidance conduit—independent of axons.
Over a period of 20 years, Archibald and his team, in collaboration with Professor Fergal O’Brien and his lab at The Royal College of Surgeons, Ireland, developed a proprietary method to allow commercial scale manufacture of a longitudinally aligned type 1 collagen-GAG nerve regeneration matrix, whose internal microscopic geometry mimics the Schwann cell basal lamina.
“Simulating properties of the native environment of Schwann cells within the lumen of the NeuraGen 3D conduit sustains and supports Schwann cell migration far more effectively than the fibrin clot that normally fills an empty conduit,” says Archibald.
Determining the Efficacy of the Collagen-GAG Matrix
In collaboration with Professor Rajiv Midha and his lab at the University of Calgary, Shakhbazau, et al.3 examined the regenerative properties of the collagen-GAG matrix, the inner structure of NeuraGen 3D matrix, in both in vitro and in vivo models in their 2014 study:
- In Vitro Testing*
In a series of in-vitro experiments, the study authors3 initially looked at Schwann cell seeding and migration on cryosections and fragments of the matrix. The Schwann cells were found to retain their morphology and send processes across the matrix. This indicated to the researchers that the collagen- GAG matrix allows for attachment and growth of Schwann cells.
Schwann cells were found3 to readily attach to and populate the volume of the collagen-GAG matrix, demonstrating that the matrix provided a highly permissive substrate for Schwann cell growth, migration, and proliferation without the need for additional growth factors.
Schwann cells were also observed3 to migrate from the pre-seeded matrix to the surrounding surface, which further demonstrated their viability. Shakhbazau et al.’s3 next experiments focused on Schwann cell migration along the longitudinal structure. Explanted fragments of rat sciatic nerve were permanently labeled with the fluorescent lipid dye DiI and subsequently plated onto segments of the collagen-GAG matrix in-vitro.
DiI fluorescence allows for evaluation of individual Schwann cell attachment and growth through the matrix. They noted extensive cell migration3 at the one and four-week time points, which demonstrated the high migratory permissivity of the collagen-GAG matrix.
- In Vivo Testing*
In the next series of experiments, the team took the collagen-GAG matrix3 from tissue culture to the in-vivo setting and analyzed Schwann cell migration into matrix tubes from both the proximal and distal ends of transected sciatic nerves in rats. After two weeks post-implantation, both proximal and distal collagen-GAG implants were heavily infiltrated with mostly p75-positive cells clustering in the central areas of the matrix.
“The matrix construct potentiated the Schwann cell colonization of the nerve guide lumen that we had observed in earlier studies” says Archibald.
In the in vivo experiments, Schwann cells readily infiltrated and adhered3 to the collagen-GAG matrix surface, using the structure as a permissive substrate. Abundant migration from the nerve proximal and distal stumps, as opposed to quite limited expansion of purified Schwann cells seeded on the matrix in vitro, may reflect the pre-conditioning of the matrix surface with endogenously-derived growth-supportive molecules in vivo, according to Archibald.
Key Takeaways from Schwann Cell Migration in the Collagen-GAG Matrix
From these results, Shakhbazau et al.3 noted the following:
- The axial alignment of collagen-GAG matrix allowed directed Schwann cell migration along the 3D linear paths and formation of long patterned columns to support axon outgrowth and myelination.
- In some areas of the matrix, Schwann cells grouped along the longitudinal structure of the matrix fibers in a manner that resembles bands of Büngner, which guide axons through the injury site back to their targets.
- Given that this phenomenon also occurred in the in vitro model with purified cultured Schwann cells, this suggests that the alignment of the Schwann cells into the linear columns may be assisted by the axial microarchitecture of the collagen-GAG matrix.
Overall, the in vivo migrating Schwann cells were found to acquire their characteristic native morphology within the matrix architecture much more easily compared to the in vitro environment.
This data, the study authors note,3 highlights the potential of the aligned collagen-GAG matrix filled conduit to support the regenerative Schwann cells.
“The launch of NeuraGen 3D Nerve Guide matrix is a culmination of many years of research and a testament to the ongoing work of countless scientists and health care practitioners to develop cutting-edge solutions for the treatment of peripheral nerve injuries,” says Archibald. “[It] has the potential to make a significant contribution to patient care.”
INDICATIONS FOR USE
NeuraGen 3D Nerve Guide Matrix is indicated for the repair of peripheral nerve discontinuities where gap closure can be achieved by flexion of the extremity.
NeuraGen 3D Nerve Guide Matrix is not designed, sold, or intended for use except as described in the indications for use and is contraindicated for patients with a known history of hypersensitivity to bovine-derived or chondroitin materials.
Do not re-sterilize
Do not use if the product package is damaged or opened
Hemostasis of the nerve stumps must be achieved prior to placement of the NeuraGen 3D Nerve Guide Matrix. A blood clot in the lumen of the nerve guide will impede axon growth.
Tensionless repair technique should be used to prevent tension along the length of the nerve.
NeuraGen 3D Nerve Guide Matrix should be used with caution within infected regions.
*Pre-clinical testing is not necessarily indicative of clinical results.
Houshyar S, Bhattacharyya A, and Shanks R. Peripheral Nerve Conduit: Materials and Structures. ACS Chem. Neurosci. 2019; 10(8): 3349-3365.
Vijayavenkataraman, S. Nerve Guide Conduits for Peripheral Nerve Injury Repair: A Review on Design, Materials and Fabrication Methods. Acta Biomater. 2020; 106: 54-69.
Shakhbazau A, Archibald SJ, Shcharbin D, Bryszewska M, Midha R. Aligned Collagen-GAG Matrix as a 3D Substrate for Schwann Cell Migration and Dendrimer-Based Gene Delivery. J Mater Sci Mater Med.2014;25(8): 1979-1989.
Madison RD, Archibald SJ. Point Sources of Schwann Cells Result in Growth into a Nerve Entubulation Repair Site in the Absence of Axons: Effects of Freeze-Thawing. Experimental Neurology. 1994; 128(2): 266-75.
Taras, JS, Jacoby SM, and Lincoski, CJ. Reconstruction of Digital Nerves with Collagen Conduits. The Journal of Hand Surgery. 2011; 36(9):1441-1446.