Application of physiologic electric fields to direct and enhance neurite outgrowth to assist in the treatment of peripheral nerve injuries

In the United States alone, there are hundreds of thousands of injuries to the peripheral nervous system (PNS) annually. Following PNS injury, damage to neural tissue and the surrounding area often results in failed axonal re-growth and a subsequent loss of function. In the past century there have been improvements in microsurgical techniques and clinically approved guidance channels have been developed for the repair of small-gap PNS injuries (less than 2 cm); however treatment options are limited for the repair of large-gap (greater than 4 cm) and/or large diameter injuries. In the absence of functional regeneration, tissue engineering strategies focusing on cellular, biophysical, biochemical, and mechanical guidance cues have been explored to promote nerve re-growth. To date these engineered strategies are unable to match or exceed the current gold standard, nerve autografts, which are in limited supply, motivating the development of new approaches.;Exogenous electrical stimulation may provide an alternative route to enhance axonal re-growth following large-gap PNS injuries. Endogenous electrical currents (<140 mV/mm) are present during embryogenesis influencing tissue organization. It is not clear if this responsiveness is retained after development and can be used to support re-growth following injury. Neurons from lower order model systems (non-mammalian) have robust regenerative capacities (i.e. Xenopus) and are responsive to exogenous electrical stimulation. It remains unknown if and how mammalian neurons and Schwann cells, glia of the PNS, will respond to exogenous electrical stimulation, a less widely studied guidance cue. To this end, my doctoral research focuses on evaluating changes to both neurons and non-neural support cells following exposure to exogenous DC electrical stimulation with the goal of promoting neurite outgrowth and enhancing the neuro-supportive Schwann cell phenotype in both 2D and 3D model environments. Furthermore, this thesis explores one potential mechanism by which electrically-stimulated Schwann cells influence neurite outgrowth via release of soluble factors.;Results indicate that primary neurons and Schwann cells are responsive to DC electrical stimulation in both 2D and 3D microenvironments. Following stimulation, Schwann cells take on an enhanced neuro-supportive phenotype that contributes to a robust increase in neurite outgrowth through electrically-induced soluble factor release mediated in-part by T-type voltage-gated calcium channels. Non-neuronal support cell (Schwann cell and endothelial cell) migration is greater within 3D hydrogels following electrical stimulation, which could aid re-vascularization and re-myelination following PNS injury. While neurite outgrowth in 2D and 3D was increased significantly by electrical stimulation, this outgrowth was uniform and not directionally biased. Since directed neurite outgrowth may more efficiently direct re-growing axons to distal targets following injury, topographical cues from highly aligned electrospun fibers were utilized in combination with electrical stimulation to drive enhanced and directed neurite extension. Optimizing exogenous electrical stimulation to manipulate both neural and non-neural support cells, while gaining a mechanistic understanding of cellular responses to the stimulus may lead to rationally designed stimulation regimes for the repair of large-gap peripheral nerve injuries.