Spinal cord injury affects nearly twenty five thousand Americans, with an additional ten thousand new injuries per year. These injuries are usually life altering due to death of nervous tissue in the spinal cord creating a void where the electrochemical signal can no longer pass. The current treatment options for such injuries are limited due to the body's inability to regenerate neurons and the difficulty in stabilizing the defect created by the injury.  This project proposes the use of a non-biodegradable hydrogel as a mechanical support to fill the injury site and provide a protected environment for the regenerating neurons. The hydrogel can be designed to match the mechanical stiffness of the local tissue to reduce the amount of stress shearing around the implant.

The use of a thermally responsive, injectable polymer, PNIPAAm-PEG branched copolymer, is proposed as a minimally invasive surgical technique. Below its LCST, typically around 29-320C, the polymer forms a miscible solution with water, but above its LCST, it becomes hydrophobic, separating from water and forming a semi porous gel. The aqueous polymer solution can be created with cell culture media and seeded with bone marrow stromal cells in order to physically entrap cells into the scaffold when it is injected into the defect. Bone marrow stromal cells (MSC) are progenitor cells that when promoted with neurotrophic factors differentiate into neuronal cells.  In order to enhance the neuronal cell proliferation, neurotrophic factors can be released in the local defect via biodegradable microparticles. Polymer microparticles allow the trophic factors to release in an initial burst, which promotes cell growth into the scaffold, and then lowers to a sustained release, which maintains the cells in the scaffold.