Aligned endothelial cell and Schwann cell structures in 3D hydrogels for peripheral nerve tissue engineering

Peripheral nerve injury can be debilitating and may result in loss of sensory or motor function. Nerve autograft remains the gold standard to repair damage that results in long gaps. The efficacy of nerve grafts, however, can be limited by necrosis at the central region. This is also a limitation in the effectiveness of cellular biomaterials developed as tissue engineered repair approaches. Although vascularised nerve grafts were introduced, some limitations such as availability of nerves and donor site morbidity need to be overcome. Therefore, there is a need for vascularised tissue-engineered nerve constructs. This study established an anisotropic nerve construct which contains self-aligned human umbilical cord vein endothelial cells (HUVECs) that form tube-like structures with and without aligned Schwann cells within a tethered collagen matrix. In an in vitro model, aligned tube-like structures supported and enhanced Schwann cell migration when compared to aligned Schwann cell-only constructs. Additionally, their efficacy to promote axonal regeneration in vitro was comparable to that of aligned Schwann cell constructs. In a rat sciatic nerve injury model, the aligned HUVEC tube-like structure constructs supported robust neuronal regeneration. HUVEC-only constructs also showed significantly improved vascularisation and Schwann cell migration at the repair site. In addition, the gel aspiration-ejection (GAE) technique offers a rapid and robust approach to produce stable anisotropic hydrogel scaffolds. This work optimised the GAE technique to generate aligned Schwann cells in collagen scaffolds. These scaffolds were stable and exhibited similar linear viscoelastic behaviours to rat sciatic nerves. They supported and promoted axonal regeneration in vivo when compared to the empty conduit groups. Together, this study has developed for the first time pre-vascularised tissue-engineered nerve constructs and shown their potential in promoting vascularisation and axonal regeneration. A novel GAE technique has also been shown to be useful in producing aligned Schwann cell-containing hydrogel constructs. In the future, the GAE system can be potentially integrated with the pre-vascularisation concept to create vascularised engineered-nerve conduits.