Nervous system injuries remain significant clinical issues that affect hundreds of thousands of individuals each year. Spinal cord injuries are especially difficult since the wound healing process results in a glial scar, inhibiting regeneration. Current strategies for dealing with spinal cord injuries focus on stabilization and rehabilitation with minimal likelihood of any significant functional regeneration. The outlook for peripheral injuries is not quite as dire as peripheral nerve has the capacity to regenerate. However, if the defect is beyond a critical size of around 1cm, that ability is compromised. The gold standard for treating large defects is an autologous nerve graft, but there are significant drawbacks. Clearly there is room for improvement.
In this study, conducting composite electrospun nanofibrous substrates were fabricated to investigate if topography and electrical stimulation could control embryonic stem cell (ESC) differentiation. First, it was determined that poly (l-lactic acid) (PLLA) nanofibers of at least 900nm promoted neuronal differentiation and neurite outgrowth. ESCs interacted with these fibers through integrin α6β1 and induced differentiation via early ERK activation. Fiber size did not have a significant effect on p38 activity. Next, PLLA was doped with polypyrrole (PPy) to improve its electrical properties. Nerve conduits fabricated with PPy/PDLLA were successful at promoting the regeneration of a rat sciatic nerve defect on par with an autologous graft. The sciatic function indices (SFI), nerve conduction velocities, triceps surae weights, and nerve fiber morphologies were all comparable between the PPy/PDLLA conduits and autografts, and both significantly better than the PDLLA conduits. Finally, PPY/PLLA was electrospun into random and aligned nanofibers. ESCs seeded on these aligned nanofibers were stimulated with 100mV for 2hrs, which induced a higher percentage of neurite-bearing cells, from around 13% to around 23%, and longer neurites, from around 80µm to around 130µm. Thus, it is clear that conducting aligned fibers combined with electrical stimulation improves ESC neurite growth. Determining the links between nanofiber-stimulated differentiation and neurogenesis allow for a better understanding of the application of ESCs in neural tissue engineering. These results provide guidance to neural tissue engineering scaffold design and insight into how ESCs interact with different topographies.PhDBiomedical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/111621/1/jmholz_1.pd
