• Artem B Kutikov, Simon W Moore, Richard T Layer, Pamela E Podell, Nithya Sridhar, Andrea J Santamaria, Alex A Aimetti, Christoph P Hofstetter, Thomas R Ulich, and James D Guest.
• InVivo Therapeutics Corporation, Cambridge, Massachusetts.
• Neurosurgery. 2019 Oct 1; 85 (4): 560-573.

BackgroundImmature neurons can extend processes after transplantation in adult animals. Neuronal relays can form between injected neural stem cells (NSCs) and surviving neurons, possibly improving recovery after spinal cord injury (SCI). Cell delivery methods of single or multiple bolus injections of concentrated cell suspensions thus far tested in preclinical and clinical experiments are suboptimal for new tract formation. Nonuniform injectate dispersal is often seen due to gravitational cell settling and clumping. Multiple injections have additive risks of hemorrhage, parenchymal damage, and cellular reflux and require additional surgical exposure. The deposition of multiply delivered cells boluses may be uneven and discontinuous.ObjectiveTo develop an injection apparatus and methodology to deliver continuous cellular trails bridging spinal cord lesions.MethodsWe improved the uniformity of cellular trails by formulating NSCs in hyaluronic acid. The TrailmakerTM stereotaxic injection device was automatized to extend a shape memory needle from a single-entry point in the spinal cord longitudinal axis to "pioneer" a new trail space and then retract while depositing an hyaluronic acid-NSC suspension. We conducted testing in a collagen spinal models, and animal testing using human NSCs (hNSCs) in rats and minipigs.ResultsContinuous surviving trails of hNSCs within rat and minipig naive spinal cords were 12 and 40 mm in length. hNSC trails were delivered across semi-acute contusion injuries in rats. Transplanted hNSCs survived and were able to differentiate into neural lineage cells and astrocytes.ConclusionThe TrailmakerTM creates longitudinal cellular trails spanning multiple levels from a single-entry point. This may enhance the ability of therapeutics to promote functional relays after SCI.Copyright © 2018 by the Congress of Neurological Surgeons.

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