PROJECT SUMMARY/ABSTRACT The long-term goal of this research is to define the mechanisms of action of a successful cell transplantation therapy for chronic spinal cord injury (SCI) and to translate this knowledge from bench to bedside for patients. Human SCI currently has no effective treatment, and any new treatments would have a significant impact on public health. The overall objective of this proposal is to determine whether transplantation of regionally specific bioprinted spinal neural progenitor cells (sNPCs) in combination with a 3D printed scaffold can result in the formation of functional neuronal networks within the injured adult rat spinal cord. We have three specific aims. The first aim is to optimize the biomaterial and design of the 3D printed scaffold, as well as the cell-laden bioink utilized in bioprinting. The second aim is to determine the optimal cell configuration of two types of regionally specific sNPCs within the scaffold to form functional neuronal networks. The third aim is to test our scaffold in a rat model of transection injury to determine whether our cells can provide a relay system across the site of injury, and whether this will result in functional recovery. We will perform detailed functional, histological, and electrophysiological analyses to elucidate the mechanisms of our combinatorial treatment. The scientific premise is that there is a synergistic relationship in providing the substrate (cells) for a relay system across the injury site and optimizing this with a conduit (scaffold), providing an effective relay for neuronal signaling leading to functional recovery.