Directing the organization of cells into a tissue with defined architectures is one use of biomaterials for regenerative medicine. To this end, hydrogels are widely investigated as they have mechanical properties similar to native soft tissues and can be formed in situ to conform to a defect. Herein, we describe the development of porous hydrogel tubes fabricated through a twostep polymerization process with an intermediate microsphere phase that provides macroscale porosity (66.5%) for cell infiltration. These tubes were investigated in a spinal cord injury model, with the tubes assembled to conform to the injury and to provide an orientation that guides axons through the injury. Implanted tubes had good apposition and were integrated with the host tissue due to cell infiltration, with a transient increase in immune cell infiltration at 1 week that resolved by 2 weeks post injury compared to a gelfoam control. The glial scar was significantly reduced relative to control, which enabled robust axon growth along the inner and outer surface of the tubes. Axon density within the hydrogel tubes (1744 axons/mm 2) was significantly increased more than 3-fold compared to the control (456 axons/mm 2), with approximately 30% of axons within the tube myelinated. Furthermore, implantation of hydrogel tubes enhanced functional recovery

One million estimated cases of spinal cord injury (SCI) have been reported in the United States and repairing an injury has constituted a difficult clinical challenge. The complex, dynamic, inhibitory microenvironment postinjury, which is characterized by proinflammatory signaling from invading leukocytes and lack of sufficient factors that promote axonal survival and elongation, limits regeneration. Herein, we investigated the delivery of polycistronic vectors, which have the potential to coexpress factors that target distinct barriers to regeneration, from a multiple channel poly(lactide-co-glycolide) (PLG) bridge to enhance spinal cord regeneration. In this study, we investigated polycistronic delivery of IL-10 that targets proinflammatory signaling, and NT-3 that targets axonal survival and elongation. A significant increase was observed in the density of regenerative macrophages for IL-10+NT-3 condition relative to conditions without IL-10. Furthermore, combined delivery of IL-10+NT-3 produced a significant increase of axonal density and notably myelinated axons compared with all other conditions. A significant increase in functional recovery was observed for IL-10+NT-3 delivery at 12 weeks postinjury that was positively correlated to oligodendrocyte myelinated axon density, suggesting oligodendrocyte-mediated myelination as an important target to improve functional recovery. These results further support the use of multiple channel PLG bridges as a growth supportive substrate and platform to deliver bioactive agents to modulate the SCI microenvironment and promote regeneration and functional recovery.

No abstract

An important role of neural stem cell transplantation is repopulating neural and glial cells that actively promote repair following spinal cord injury (SCI). However, stem cell survival after transplantation is severely hampered by the inflammatory environment that arises after SCI. Biomaterials have a demonstrated history of managing post-SCI inflammation and can serve as a vehicle for stem cell delivery. In this study, we utilize macroporous polyethylene glycol (PEG) tubes, which were previously found to modulate the post-SCI microenvironment, to serve as a viable, soft substrate for injecting mouse embryonic day 14 (E14) spinal progenitors 2 weeks after tube implantation into a mouse SCI model. At 2 weeks after transplantation (4 weeks after injury), 4.3% of transplanted E14 spinal progenitors survived when transplanted directly into tubes compared to 0.7% when transplanted into the injury alone. Surviving E14 spinal progenitors exhibited a commitment to the neuronal lineage at 4 weeks post-injury, as assessed by both early and late phenotypic markers. Mice receiving tubes with E14 spinal progenitor transplantations had on average 21 ± 4 axons/mm 2 regenerated compared to 8 ± 1 axons/mm 2 for the injury only control, which corresponded with a significant increase in remyelination compared to the injury only control, while all conditions exhibited improved forelimb control 4 weeks after injury compared to the injury only. Collectively, we have demonstrated the feasibility of using PEG tubes to modify the implantation site and improve survival of transplanted E14 spinal progenitors.