Schwann Cells Enhance Penetration of Regenerated Axons into Three-Dimensional Microchannels

Abstract

Nerve regeneration after injury requires proper axon alignment to bridge the lesion site and myelination to achieve functional recovery. Transplanted scaffolds with aligned channels, have been shown to induce axon growth to some extent. However, the penetration of axons into the microchannels remain a challenge, influencing the functional recovery of regenerated nerves. We previously demonstrated that the size of microchannels exerts significant impact on Schwann cells (SCs) migration. Here we demonstrate that migration of SCs promotes, significantly, the dorsal root ganglion (DRG) neurons to extend axons into three-dimensional channels and form aligned fascicular-like axon tracts. Moreover, the migrating SCs attach and wrap around the aligned axons of DRG neurons in the microchannels and initiate myelination. The SCs release growth factors that provide chemotactic signals to the regenerating axons, similar to the response achieved with nerve growth factor (NGF), but with the additional capability of promoting myelination, thereby demonstrating the beneficial effects of including SCs over NGF alone in enhancing axon penetration and myelination in three-dimensional microchannels.

Bioactive 3D Scaffolds for the Delivery of NGF and BDNF to Improve Nerve Regeneration

“…2,000 and ca. 2,500 µm respectively for both DRG seeded with Schwann cells and collagen-loaded NGF (Liu et al, 2018).…”

“…However, due to the half-life of the growth factors, it is essential to design a system which stabilises and delivers growth factors with the purpose of extending the half-life of growth factors, and hence reducing the amount required, and to maintain a sustained delivery of these during the healing process. Liu et al fabricated micropatterned channels scaffold with polydimethyl-siloxane (PDMS) (Liu et al, 2018). Then, DRG were co-cultured with Schwann cells for 21 days to study neurite outgrowth.…”

“…Although studies using aligned fibrous scaffold have stimulated neurite outgrowth, the level of nerve regeneration produced is still not sufficient (for example, 2.1 ± 0.33 mm, 1.4 mm), as the critical nerve gap in humans is 4 cm, and in rats is 1.5 cm (Wang et al, 2010;Kaplan et al, 2015;Behbehani et al, 2018). An interesting route to further enable nerve repair is to include chemical cues in the NGCs to provide a long term permissive environment (Chwalek et al, 2016;Liu et al, 2018).…”

Neuronal substrates alter the migratory responses of nonmyelinating Schwann cells to controlled brain‐derived neurotrophic factor gradients

“…The significance of MN substrates for nmSC motility and directedness is evident physiologically, as terminal SCs adhere tightly to the surface of MN axons, in vivo, rather than wrap them (Jones et al, ; Nishimune & Shigemoto, ), suggesting innate haptotactic attraction. Further, MNs are believed to secrete neurotrophins that repel wrapping behavior of terminal SCs as a means to protect the synaptic cleft and communication therein (Liu, Kray, & Chan, ; Monk, Feltri, & Taveggia, ). Cell adhesion molecules, such as N‐CAM1, between terminal SCs and MNs have been targeted for their large role(s) in regeneration, but mechanisms of action remain only partially understood.…”

Fabrication of Microchannels and Evaluation of Guided Vascularization in Biomimetic Hydrogels

“…Manufactured microchannels play an important role in delivering oxygen and nutrients to the cells in the hydrogel to improve cell viability and function. To fabricate microchannels in a large-scale hydrogel, various techniques such as fiber bonding [16], electrospinning [17], PDMS molding [18] and 3D printing [19][20][21] have been introduced in hydrogels by using 3D fabrication technologies [22]. Recently, 3D printing techniques have been attracting attention because of the merits of solid freeform fabrication and guaranteed interconnectivity.…”