Graphene-Based Materials Prove to Be a Promising Candidate for Nerve Regeneration Following Peripheral Nerve Injury

Abstract

Peripheral nerve injury is a common medical condition that has a great impact on patient quality of life. Currently, surgical management is considered to be a gold standard first-line treatment; however, is often not successful and requires further surgical procedures. Commercially available FDA- and CE-approved decellularized nerve conduits offer considerable benefits to patients suffering from a completely transected nerve but they fail to support neural regeneration in gaps > 30 mm. To address this unmet clinical need, current research is focused on biomaterial-based therapies to regenerate dysfunctional neural tissues, specifically damaged peripheral nerve, and spinal cord. Recently, attention has been paid to the capability of graphene-based materials (GBMs) to develop bifunctional scaffolds for promoting nerve regeneration, often via supporting enhanced neural differentiation. The unique features of GBMs have been applied to fabricate an electroactive conductive surface in order to direct stem cells and improve neural proliferation and differentiation. The use of GBMs for nerve tissue engineering (NTE) is considered an emerging technology bringing hope to peripheral nerve injury repair, with some products already in preclinical stages. This review assesses the last six years of research in the field of GBMs application in NTE, focusing on the fabrication and effects of GBMs for neurogenesis in various scaffold forms, including electrospun fibres, films, hydrogels, foams, 3D printing, and bioprinting.

Keywords: biomedicine; drug delivery; functionalized graphene oxide; graphene-based materials; nerve differentiation; nerve proliferation; nerve tissue engineering; nervous system; plastic surgery; regenerative medicine; spinal cord injury; surgery.

Figure 1

Introduction of nervous system. (Illustrated by authors and utilising a real image of damaged myelin [33]).

Figure 2

Due to the damage, the axons and myelin are fragmented at the injury site. Dedifferentiation and proliferation of mature myelinating Schwann cells occur. Then, after dedifferentiation, myelin and axonal debris are removed by Schwann cells or by recruiting circulating macrophages and producing neurotrophic factors that support axon regeneration. Schwann cells downregulate myelin-associated genes, which are vital for myelinations such as Krox20/Egr-235, and re-express molecules correlated with immature states such as the p75 neurotrophin receptor (p75NTR) and the neural cell adhesion molecule (NCAM). Reused with permission [10].

Figure 3

Schematic of graphene (G), graphene oxide (GO), reduced graphene oxide (rGO) and functionalized graphene (FGO) materials in nerve tissue engineering, both in vitro and in vivo, in various forms of scaffolds, such as film, electrospun mat, foam or sponge, hydrogel, 3D print, and conduit.

Figure 4

(A,B) exhibiting the morphology of electrospun mats by increasing the GBMs concentration. Reused with permission from [44,45].

Figure 5

The schematic illustration of ES effect on neural injury regeneration (A) Injured neuron without the conductive platform and electrical stimulation, (B) Injured neuron exposed conductive platform and electrical stimulation. Reused with permission from [6].

Figure 6

(A) Mechanism of the engineered system of GO-based gene delivery that induces differentiation of recruited BMSCs for cutaneous nerve regeneration. Reused with permission from [69]. (B) Immunofluorescence images indicate the structure of the injured spinal cords and the distribution of three important marker proteins: glial fibrillary acidic protein (GFAP), microtubule-associated protein 2 (MAP-2), and neuron-specific class III β-tubulin (TUJ-1). Scale bar: 500 μm. Reused with permission from [70].

Figure 7

3D bioprinting structure made of PU/G. (A) Side view, (B) top view of the construct, and (C) image of neural stem cells encapsulated in the scaffold. Cells were labelled with PKH26 (red fluorescence). Reused with permission from [81].

Figure 8

(A) Schematic of netrin-1-loaded GMT/hydrogel conduit preparation. (a,b) Growing G onto a nickel mesh (CVD method), (c) covering G/nickel mesh with a precursor solution, (d) formation of strong ionic bonds between alginate and Ca²⁺ ions due to immersing GMT into CaCl₂ solution, (e,f) polymerization of GelMA under UV light, (g) etching nickel template, and (h) Immersing the conduit in high concentrated netrin-1 solution, (i) peripheral nerves regeneration. Reused with permission from [95]. (B) Images of regeneration of muscle after NGC implantation in different groups. Reused with permission from [97].

Figure 9

(A) Schematic of projected collagen graphene cryogel mechanism: due to spinal cord injury, inflammatory cytokines and infiltration of inflammatory cells have been produced. By implanting the cryogels, it will promote proliferation and stemness maintenance of BM-MSCs and secrete anti-inflammatory biomolecules. Further, the presence of cryogels and macrophage infiltration will stimulate high polarization of the M2/M1 phenotype. Reused with permission from [98]. (B) The illustration depicts the PLCL film fabrication with stripe micropatterns and GO nanosheets and its use in four steps: (1) creating micropatterns by thermal pressing of a polydimethylsiloxane template onto a PLCL film, (2) aminolyzing by 1,6-hexanediamine then GO adsorption electrostatically, (3) manufacturing micropatterned PLCL/GO conduit, and (4) implanting into a rat with sciatic nerve defects. The middle schematic shows that the micropatterned PLCL/GO film can improve the directional migration of Schwann cells from their cell spheroids, induce the macrophages differentiation into M2 type, and guide the neurites of N2a cells along with the patterns. Reused with permission from [99].