Influence of Touch-Spun Nanofiber Diameter on Contact Guidance during Peripheral Nerve Repair.

Peripheral nerve regeneration across large gaps remains clinically challenging and scaffold design plays a key role in nerve tissue engineering. One strategy to encourage regeneration has utilized nanofibers or conduits to exploit contact guidance within the neural regenerative milieu. Herein, we report the effect of nanofiber topography on two key aspects of regeneration: Schwann cell migration and neurite extension. Substrates possessing distinct diameter distributions (300 ± 40 to 900 ± 70 nm) of highly aligned poly(ε-caprolactone) nanofibers were fabricated by touch-spinning. Cell migratory behavior and contact guidance were then evaluated both at the tissue level using dorsal root ganglion tissue explants and the cellular level using dissociated Schwann cells. Explant studies showed that Schwann cells emigrated significantly farther on fibers than control. However, both Schwann cells and neurites emigrated from the tissue explants directionally along the fibers regardless of their diameter, and the data were characterized by high variation. At the cellular level, dissociated Schwann cells demonstrated biased migration in the direction of fiber alignment and exhibited a significantly higher biased velocity (0.2790 ± 0.0959 µm·min-1) on 900 ± 70 nm fibers compared to other nanofiber groups and similar to the velocity found during explant emigration on 900 nm fibers. Therefore, aligned, nanofibrous scaffolds of larger diameters (900 ± 70 nm) may be promising materials to enhance various aspects of nerve regeneration via contact guidance alone. While cells track along with the fibers, this contact guidance is bidirectional along the fiber, moving in the plane of alignment. Therefore, the next critical step to direct regeneration is to uncover haptotactic cues that enhance directed migration.

Transcorneal Electrical Stimulation Reduces Neurodegenerative Process in a Mouse Model of Glaucoma.

Glaucoma is a neurodegenerative disease in which the retinal ganglion cell axons of the optic nerve degenerate concomitant with synaptic changes in the retina, leading finally to death of the retinal ganglion cells (RGCs). Electrical stimulation has been used to improve neural regeneration in a variety of systems, including in diseases of the retina. Therefore, the focus of this study was to investigate whether transcorneal electrical stimulation (TES) in the DBA2/J mouse model of glaucoma could improve retinal or optic nerve pathology and serve as a minimally invasive treatment option. Mice (10 months-old) received 21 sessions of TES over 8 weeks, after which we evaluated RGC number, axon number, and anterograde axonal transport using histology and immunohistochemistry. To gain insight into the mechanism of proposed protection, we also evaluated inflammation by quantifying CD3+ T-cells and Iba1+ microglia; perturbations in metabolism were shown via the ratio pAMPK to AMPK, and changes in trophic support were tested using protein capillary electrophoresis. We found that TES resulted in RGC axon protection, a reduction in inflammatory cells and their activation, improved energy homeostasis, and a reduction of the cell death-associated p75NTR. Collectively, the data indicated that TES maintained axons, decreased inflammation, and increased trophic factor support, in the form of receptor presence and energy homeostasis, suggesting that electrical stimulation impacts several facets of the neurodegenerative process in glaucoma.

RGD-Modified Nanofibers Enhance Outcomes in Rats after Sciatic Nerve Injury.

Nerve injuries requiring surgery are a significant problem without good clinical alternatives to the autograft. Tissue engineering strategies are critically needed to provide an alternative. In this study, we utilized aligned nanofibers that were click-modified with the bioactive peptide RGD for rat sciatic nerve repair. Empty conduits or conduits filled with either non-functionalized aligned nanofibers or RGD-functionalized aligned nanofibers were used to repair a 13 mm gap in the rat sciatic nerve of animals for six weeks. The aligned nanofibers encouraged cell infiltration and nerve repair as shown by histological analysis. RGD-functionalized nanofibers reduced muscle atrophy. During the six weeks of recovery, the animals were subjected to motor and sensory tests. Sensory recovery was improved in the RGD-functionalized nanofiber group by week 4, while other groups needed six weeks to show improvement after injury. Thus, the use of functionalized nanofibers provides cues that aid in in vivo nerve repair and should be considered as a future repair strategy.