Hydrogel Composite as a Nucleus Pulposus Replacement Designed to Resist Extrusion While Maintaining Functional Material Properties

This study pursues the design of a nucleus pulposus replacement device which can be placed using minimally invasive surgical techniques, has the correct material properties, and resists extrusion. A composite of open-celled foam and agar was studied in both unconfined and confined compression, the latter with a simulated annular defect (radial tear simulation). It was found that by compositing the agar into the open-cell foam, there is an increase in the yield strength and stiffness in unconfined compression. In the radial tear simulator, the composite material exhibited linearly increasing stress to further extrusion after the initial yield compared to the agar, which exhibited no increase in stress for continued extrusion after the yield point.