Optogenetic-Enabled Biomanufacturing of Long-Projecting Motor Tracts for Neural Reconstruction

Tissue-engineered spinal tracts are designed to restore long-distance axonal connectivity after neurotrauma but are constrained by the slow intrinsic growth of many neuronal subtypes, particularly spinal motor neurons. Optogenetic stimulation enables precise, cell-type-specific control of neuronal activity and represents a potential strategy to accelerate axonal assembly during neural tissue biomanufacturing. Here, spinal motor neuron aggregates derived from embryonic rat spinal cord were encapsulated within agarose hydrogel micro-columns to generate three-dimensional tissue-engineered spinal tracts. Neurons were transduced to express the red-shifted channelrhodopsin ChrimsonR and subjected to patterned red-light stimulation. Stimulation parameters were first screened in planar cultures to identify biologically effective conditions, then applied to three-dimensional constructs. Tissue-engineered spinal tracts were stimulated once at 7 days in vitro using a 1-hour, 10 Hz optical paradigm and maintained in culture through 21 days in vitro. Axonal extension within the micro-column lumen was quantified and compared across transduced and non-transduced conditions with and without optical stimulation. Optogenetically transduced constructs exhibited robust axonal growth with preserved neuronal health and organized tract architecture. While transduction alone enhanced axonal extension relative to non-transduced controls, a single bout of optogenetic stimulation further accelerated growth in transduced constructs, yielding an approximately 2.5-fold increase in axonal length by 21 days in vitro. No light-dependent effects were observed in non-transduced neurons, indicating that enhanced growth required both opsin expression and patterned optical stimulation. These findings demonstrate that brief, targeted optogenetic activation is sufficient to accelerate axonal elongation during three-dimensional neural tissue fabrication. Optogenetic stimulation therefore represents a programmable and scalable biomanufacturing input for accelerating the assembly of long-projecting engineered neural tissues through activity-dependent mechanisms. .