PROJECT SUMMARY The drug development pipeline is plagued by unacceptable rates of attrition due in large part to toxicities that are not identified in pre-clinical stages of development. The ability to de-risk lead compounds during pre-clinical development with advanced ?organoid-on-a-chip? technologies shows tremendous promise. Drug-induced neurotoxicity is caused by off-target effects of pharmaceuticals that lead to sensory, motor, and cognitive deficits. While rarely fatal, drug-induced neurotoxicity can lead to permanent nerve damage and in some cases can be a dose-limiting side effect, leading patients to reduce dosage or stop treatment altogether. Although the peripheral nervous system bears the brunt of this neurological toxicity, development of microphysiological models of the peripheral nervous system is lagging. Towards that end, the technology described herein allows for 3D growth of high density axonal fiber tracts, resembling peripheral nerve anatomy. Progress during the prior award phase strongly demonstrated the feasibility of using microengineered neural tissues that are amenable to morphological and physiological measurements analogous to those of clinical tests. The use of structural and functional analyses should mean drug-induced neural toxicity will manifest in these measurements in ways that mimic clinical neuropathology. The goals of this proposal are to establish our human model using relevant physiological measurements in tissues fabricated from human iPS cells, and to validate the model system with a library of compounds, comparing against conventional cell culture models. Validating the peripheral nerve model system with drugs known to induce toxicity via a range of mechanisms will demonstrate the ability of the system to predict various classifications of neuropathy, yielding a high-content assay far more informative than traditional in vitro systems.