| Multiple channel bridges were developed to stimulated nerve regeneration after spinal cord injury. They were made of poly (lactide-co-glycolide) and fabricated with a gas foaming/particulate leaching technique. After implantation in a rat spinal cord lateral hemisection model, bridges supported substantial cell infiltration, aligned cells within the channels, and stimulated axon growth across the lesion site. Bridges coated with extracellular matrix components, such as fibronectin, laminin, and IKVAV peptide amphiphiles, did not affect nerve growth or the identity of cells that infiltrated the bridge.;Bridges were encapsulated with 800 microg plasmid DNA to promote gene transfer after spinal cord injury. High levels of transgene expression were observed at the implant site up to two weeks with decreasing levels rostral and caudal. Immunohistochemistry revealed that the transfected cells in the bridge were mainly identified as Schwann cells, fibroblasts, and macrophages. Surface-mediated DNA delivery from multiple channel bridges was applied to immobilize DNA lipoplexes to the bridge post-fabrication. In vitro studies revealed that the incubation of lipoplexes on fibronectin coated bridges led to the greatest immobilization efficiencies and expression levels. In vivo, lipoplexes immobilized to the bridge produced transgene expression levels that were 2-fold greater than naked plasmid and persisted for at least three weeks after spinal cord injury.;Patterning of gene delivery on sub-millimeter length scales within the bridge can provide a fundamental technology to recreate the complex architecture of the spinal cord. A mixture of lipoplexes and fibronectin was pipetted and dried within the 250 microm channels of the bridge, resulting in patterned transgene expression of multiple proteins and localized neurite extension in vitro, and transgene expression in vivo within the bridge.;Finally, proteins, such as neurotrophic and angiogenic factors, were delivered from the bridge by combining protein pre-encapsulation inside the microspheres and protein mixing with the microspheres before gas foaming. In vivo, a low dose of NT-3 enhanced the regeneration of motor neurons inside the bridge, while a high combined dose of VEGF and FGF-2 resulted in an increase of blood vessel ingrowth, endothelial cell infiltration, and neurite extension inside the lesion. |
