PROJECT SUMMARY There is a clinical need for an effective neural guidance conduit to treat long gap peripheral nerve injuries. Many studies have explored different materials and active cues to guide neural regeneration, with some success. However, none have demonstrated a comparable or better functional recovery than the gold standard autograft. An autograft requires an additional surgery to remove a sensory nerve such as the sural nerve from the patient which can lead to loss of sensation. Additionally, an autograft is not a sufficient treatment to restore function for large gap injuries to the brachial plexus and sciatic nerves. We hypothesize that a synergistic combination of physical, cellular, and biochemical guidance cues is required to achieve robust functional recover on par or better than that provided by an autograft. A 3D printed conduit can be designed to match the size of the injury defect for patient specific care. Rapid Projection, Image-guided, Direct Printing (RaPID) is capable of producing true-3D cell-laden hydrogel constructs with microscale features on the order of seconds to minutes. Schwann cells play a key role in endogenous peripheral nerve regeneration by releasing neurotrophic factors to both sustain and guide the regenerating axons. GDNF is a neurotrophic factor of high interest for its role in motor neuron regeneration. The authors plan to address the hypothesis by first genetically engineering Schwann cells to overexpress GDNF, then anchoring them via photochemistry along the length of the 3D-printed multi- microchannel conduit in a density gradient pattern to create a persistently generated soluble GDNF gradient. Once validated, the authors plan to run an in vivo study in a murine sciatic nerve injury model to access the functional recovery efficacy of the synergistic conduit versus the acellular conduit and autograft. This proposal addresses the NINDS mission of reducing the burden of neurological disease for every age group and segment of society by developing a tailored-to-patient conduit with synergistic cues for enhanced restoration of function after a PNI.