Enhanced Femoral Nerve Regeneration After Tubulization with a Tyrosine-Derived Polycarbonate Terpolymer: Effects of Protein Adsorption and Independence of Conduit Porosity

Abstract

Following complete nerve transection, entubulation of the nerve stumps helps guide axons to reconnect distally. In this study, a biodegradable and noncytotoxic tyrosine-derived polycarbonate terpolymer composed of 89.5 mol% desaminotyrosyl tyrosine ethyl ester (DTE), 10 mol% desaminotyrosyl tyrosine (DT), and 0.5 mol% poly(ethylene glycol) (PEG, molecular weight [Mw] = 1 kDa) [designated as E10-0.5(1K)] was used to fabricate conduits for peripheral nerve regeneration. These conduits were evaluated against commercially available nonporous polyethylene (PE) tubes. The two materials are characterized in vitro for differences in surface properties, and the conduits are then evaluated in vivo in a critical-sized nerve defect in the mouse femoral nerve model. Conduits were fabricated from E10-0.5(1K) in both porous [P-E10-0.5(1K)] and nonporous [NP-E10-0.5(1K)] configurations. The results illustrate that adsorption of laminin, fibronectin, and collagen type I was enhanced on E10-0.5(1K) compared to PE. In addition, in vivo the E10-0.5(1K) conduits improved functional recovery over PE conduits, producing regenerated nerves with a fivefold increase in the number of axons, and an eightfold increase in the percentage of myelinated axons. These increases were observed for both P-E10-0.5(1K) and NP-E10-0.5(1K) after 15 weeks. When conduits were removed at 7 or 14 days following implantation, an increase in Schwann cell proteins and fibrin matrix formation was observed in E10-0.5(1K) conduits over PE conduits. These results indicate that E10-0.5(1K) is a pro-regenerative material for peripheral nerves and that the porosity of P-E10-0.5(1K) conduits was inconsequential in this model of nerve injury.

Porous and Nonporous Nerve Conduits: The Effects of a Hydrogel Luminal Filler With and Without a Neurite-Promoting Moiety

“…34 Porous and nonporous conduits 5 mm in length were fabricated using a dip-coating method as described. 28 In brief, the nonporous conduits were made by repeatedly dip coating a mandrel in a solution of 900 mg of E10-0.5(1K) in 3 mL of methylene chloride, followed by drying. The porous conduits were made in the same way by dip coating the mandrel in a solution of 450 mg of E10-0.5(1K) in 3 mL of methylene chloride that also contained 450 mg of crystals sieved to a size of 25-45 mm, followed by drying and then by leaching in water to remove the sugar crystals.…”

“…28,32,37 Animals were trained to perform a classical beam test before implantation of the conduit. Postsurgery, this test was performed weekly until the endpoint of the experiment.…”

“…28,31 Total number of myelinated axons per nerve cross section, raw tissue area, cross-sectional area of the regenerating cable, and the percentage of nerve regeneration were measured with ImageJ.…”

“…We reported on the use of this terpolymer to facilitate nerve regeneration previously. 28 We are now reporting on the continuation of our studies, exploring the complex in vivo relationship between the porosity of the conduit wall and the material used to fill the inner lumen of the conduit.…”

“…Since one of the biological activities of glycan human natural killer cell antigen-1 (m-HNK) is to support preferential motor neuron targeting, we have used the mouse femoral nerve model in this and other studies. 28 Four specific conduit conditions were evaluated as shown in Table 1. Conduits had either a porous or nonporous outer wall and were filled with either a general cell friendly matrix (collagen), shown to effectively improve nerve regeneration after peripheral nerve injury, 10,11 or a neurite-specific promoting matrix (CollagenHNK) containing a glycomimetic of the m-HNK.…”