Spinal cord axons have the capacity to regenerate following injury. However, functional improvement following spinal cord injury (SCI) in patients and in experimental animal models has been elusive. We have brought together a new research group combining expertise in polymer-based tissue engineering, cellular and molecular neurobiology, spine surgery, neurosurgery, and spinal cord injury. We have developed a series of novel biodegradable polymer implants for use in the treatment of SCI. Pilot studies of the implant in the rat transected spinal cord model demonstrated the potential for promoting axon regeneration. Implants were well-tolerated in the spinal cord and were loaded with Schwann cells that survive. During three months after implantation, there was axon growth throughout the length of the graft. We hypothesize that the implant can serve as a scaffold to support axon growth across a gap, as a source of supporting cells, and as a vehicle for controlled local delivery of agents that promote regeneration. We now propose to systematically manipulate the structural, cellular and molecular environment of the regenerating cord. In the first aim, we will study the degradation characteristics and biocompatibility of two polymers; poly (lactic-coglycolic)acid (PLGA) and poly(caprolactone fumarate) (PCLF). We will use computer-aided design to generate the three-dimensional structure of the scaffold and then determine whether vacuum molding or free-form fabrication (micro-printing) produces the best architecture. In the second aim we will examine the effect of scaffold geometry on regeneration by testing PLGA and PCLF scaffolds with varying diameter channels. The number and direction of axons regenerating through the scaffolds will be measured. In the third aim we will compare the ability of two cell types (primary Schwann cells and a Schwann cell line;SpL201) to support regeneration and to act as a source of biomolecules that promote regeneration. In the fourth aim we will examine the role of the biodegradable polymer as a delivery vehicle for therapeutic agents. Chondritinase-ABC will be used as a model protein. It is an enzyme that enhances axonal regeneration in the cord. Delivery of active enzyme after encapsulation in microspheres or in the graft will be compared and the effect of enzyme delivery in the regenerating cord will be assessed. Imaging with Micro-CT and MR microscopy will be combined with histological and functional assessments to measure success in promoting regeneration.
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