Engineering approaches for nerve repai

Spinal cord injury (SCI) has been shown to result in devastating consequences including temporary or permanent deficit in sensory as well as motor function. The regeneration of nerves is found to be a chaotic process due to unorganized axon alignment. Therefore, properly organized axonal alignment is necessary to bridge the lesion site. Furthermore demyelination after SCI strongly impairs the conductive capacity of surviving axons, remyelination is critical for proper function of the regenerated nerves. Schwann cells (SCs) migrate and aid both spinal cord and peripheral nerve injury repairs, as SCs are responsible for remyelination of the regenerated axons and provide guidance for regrowing axons. Therefore, SC migration is a key in axon regeneration and remyelination. This study focuses on developing engineering approaches to enhance axon regeneration and SC migration to promote remyelination. We first demonstrate that mesenchymal stem cells aligned on pre-stretch induced anisotropic surface due to sensing a larger effective stiffness in the stretched direction than in the perpendicular direction. Next we show that an anisotropic surface arising from mechanical pre-stretch impacts axonal alignment and myelination. Culturing dorsal root ganglia (DRG) neuron cells on pre-stretched surfaces induced alignment of the regenerated axons in the direction of the pre-stretch, and further increased the thickness of the axons over those on an unstretched surface. Subsequent co-culture of the DRGs with the SCs showed preferential attachment of the SCs to the aligned axons and expression of the myelin component protein P0 by the SCs. Taken together the results establish that a pre-stretch induced anisotropic surface enhances axon alignment, thickness, and myelination. SCs play an instrumental role in aiding nerve repair. To better optimize the design of transplantable scaffolds, we studied the influence of channel diameter on the migration behavior of large populations of SCs over a period of two weeks. Micropatterned polydimethylsiloxane (PDMS) channel surfaces with different channel sizes served to mimic the varying channel sizes of transplantable scaffolds in vitro. The average cell migration speeds were quantified and normalized using two methods. We found higher SC migration speeds on PDMS channels with decreasing channel sizes. These results suggest that scaffold channel size provides a means to manipulate SC migration into the scaffold for nerve repair. Finally to test the axon growth in microchannels, we further co-cultured DRGs and SCs at opposite ends of micropatterned channels of varying sizes. Freshly isolated DRGs were seeded at one end of the channels and SCs were seeded at the other end to provide growth factors to the axons. As a positive control, in lieu of SCs, collagen gel pre-loaded with Nerve Growth Factor (NGF) was added at one end of the channels. The results indicate that the addition of SCs or the NGF encapsulated gel effectively attracted axons to penetrate into the microchannels as compared to the negative control (blank control without SCs or NGF).