Spinal cord tissue engineering using electrically conductive scaffolds

Over 500,000 people suffer a spinal cord injury (SCI) every year worldwide, often causing significant loss in quality of life for SCI sufferers. Current clinical treatments focus on minimisation of the initial injury but there are limited options available for anabolic replacement of lost tissue. Electrically conductive (EC) hydrogels have been investigated for SCI treatment. Despite success in stimulating increased axonal growth in vivo, few studies have combined EC hydrogels with stem cells to further spinal cord regeneration, despite identification of promising cell types. This project developed an EC hydrogel for spinal cord tissue engineering applications, and tested the construct using both model neuronal cells and dental pulp stem cells (DPSCs). This was achieved through initial optimisation of crosslinking efficiency and Young’s Modulus through crosslinker selection in a gelatin-norbornene (GelNOR) hydrogel. This hydrogel was then combined with EC gold nanorods (GNRs) to improve electrical conductivity, before being biologically tested using either normal human dermal fibroblasts (nHDFs) or DPSCs and finally with a model coculture system, also developed in this project, of either cell type with PC12s. The experiments found that the GelNOR hydrogel’s physical properties were optimised at 10 wt% when crosslinked with dithiothreitol (DTT) at a 3:1 norbornene:thiol ratio. Physical properties of GelNOR were conserved whilst electrical conductivity was significantly increased at 0.5 mg/ml GNR concentration, and this resulted in improved neurite outgrowth from PC12s in co-culture with nHDFs in the EC hydrogel. DPSCs acted to increase PC12 proliferation in native GelNOR but were adversely affected by GNR presence in the final constructs. Increased neurite extension in the EC vs native hydrogel shows the potential of GNR/GelNOR hybrid hydrogel for use in SCI repair, and the ability of DPSCs to improve proliferation of neural cells in GelNOR shows the potential of DPSCs and GelNOR for use in SCI repair.