Creating a three-dimensional nerve bridge: translating a laboratory device into a surgical product

Abstract

Nervous system injuries represent serious burdens to both those afflicted, and to global healthcare, costing several billions each year to manage. Whilst functional recovery is possible with minor injuries, current treatments fall short in the more severe cases, and more refined treatment options are needed in order to relieve both the physical and economic burdens. The development of cell transplantation therapies utilising biomaterials as a scaffold has garnered attention in recent years, however there is still debate over which materials to use, and how they should be employed. This project has three goals: to identify a suitable hydrogel candidate for supporting growth of glia for a peripheral nerve transplantation therapy; to determine changes in gene expression of Schwann cells infused into the best hydrogel candidate; and to determine the efficacy of a Schwann cell-infused hydrogel nerve conduit on the regeneration of a full sciatic nerve transection injury in mice. Firstly, we profiled five biomaterials and evaluated their potential for use for cellular transplantation therapies, with the aim of improving the post-transplantation survival rate of the encapsulated cells. Using live dead assays, along with 3D imaging techniques, we found that there were no significant reductions in cell viability when encapsulating cells in hydrogels at the high seeding densities required for transplantation. From these results we determined that sodium alginate was the most appropriate hydrogel for our purposes and developed a sodium alginate nerve conduit designed to deliver Schwann cells into a peripheral nerve injury.\nSecondly, we developed a surgical method for transplanting cell-infused hydrogel conduit into a full sciatic nerve transection injury model in mice. We found that transplanting a sodium alginate filled conduit had a significant effect on the regeneration of a full sciatic nerve transection, whilst the addition of Schwann cells seemed to have little impact.\nFinally, to ascertain why the Schwann cell transplantation did not produce more tangible results, we used NextGen sequencing to identify changes in gene expression by Schwann cells between two methods of 3D cell culture, hydrogel encapsulation and spheroids, and 2D monolayer cultures. There Creating a three-dimensional nerve bridge: translating a laboratory device into a surgical product were minimal differences between the two 3D culture methods. More importantly, however, there were significant differences in the gene expression profiles between the 2D and 3D culture methods, with a heavy upregulation of immune response genes, and a downregulation of genes crucial to facilitating nerve regeneration. We determined that these gene expression changes in the 3D culture methods were unfavourable in the context of nerve injury treatment, and was likely the cause of the lack of difference between the sodium alginate filled conduit and Schwann cell transplantation groups in our surgeries. However, more experiments need to be performed in order to substantiate these results.\nOverall, this thesis demonstrates that sodium alginate hydrogel is suitable for generating nerve conduits and for embedding cells. However, Schwann cells in the 3D format had an unfavourable expression profile and future work should explore avenues for improving cell growth within 3D constructs. With these results, we hope to further develop a therapy that can be used to treat acute traumatic PNS injuries in humans, and potentially translate across to treating more serious nerve injuries such as traumatic brain or spinal cord injuries.