Peripheral nerve injury (PNI) is increasingly common with over 200,000 peripheral nerve repairs performed every year in the United States. Common causes of PNI include trauma, tumor excision, and iatrogenic injury. The current gold standard for nerve repair is the autologous nerve graft (autograft) wherein a healthy sensory nerve is taken from another part of the body to repair injured nerve. However, only about 40-50% of patients receiving autograft treatment exhibit adequate functional recovery. This is likely due to the differences in sensory versus motor axon guidance. A major developmental mechanism of axon guidance is axon facilitated axon guidance, where a pioneer axon reaches the end target first, followed by the bolus of growing axons that use the pioneer axon as a guide;​ this is also seen in vitro when motor neurons and sensory neurons are co-cultured.

Current nerve repair strategies do not take into consideration modality dependent axon regeneration. To address this, we have utilized the technique of axon stretch-growth to develop tissue engineered nerve grafts (TENGs) consisting of long, aligned axon tracts. We have previously reported the efficacy of TENGs in bridging critical nerve gap lengths. These first generation TENGs were comprised of pure sensory stretch grown axons. Here we expand this technology to include motor and mixed motor-sensory stretch grown axons to better suit different nerve types. Motor and mixed motor-sensory TENGs were fabricated by implementing the technique of forced neuronal aggregation and culturing these motor aggregates in custom-built mechanobioreactors. These stretch grown constructs were then used as a testbed to determine key molecular mediators of axon guidance by analyzing expression levels of specific cell adhesion molecules (CAMs) in sensory and motor TENGs over time and the effect of stretch growth on CAM expression. Lastly, sensory, motor, and mixed motor-sensory TENGs were transplanted into a rat sciatic nerve injury model to determine the regenerative efficacy of these modality specific constructs. Electrophysiological and nerve and muscle morphometry assessments confirmed that inclusion of motor axons into the constructs improved functional regeneration outcomes.