Structure and mechanical properties of supercritical carbon dioxide processed porous resorbable polymer constructs

Current bone graft substitute materials do not address the complex architectural and biomechanical requirements to achieve a successful spinal fusion. The development of porous, structural constructs for use in spinal fusion surgeries is thus an area of intense interest. Numerous techniques have been introduced to fabricate porous resorbable polymer constructs. However, these techniques have been associated with the use of potentially harmful organic solvents, and resulted in materials with less than optimal properties. Supercritical carbon dioxide (scCO₂) processing appears to be a promising technique for producing reinforced biodegradable foams. The structure, mechanical properties and water uptake capacity of PDLGA constructs processed with scCO₂ were examined. Porous morphology of the constructs was found to depend strongly on processing temperature and the confinement of the structures after processing. The resulting constructs had a dense "cortical" shell about 15-20 μm thick and an interconnected porous core with pore diameters in the range of 236-239 μm, similar to iliac crest bone grafts currently used in spinal fusion procedures. Mechanical properties and the water uptake capacity of the constructs were found to depend on the glycolic acid content (copolymer composition). Supercritical CO₂ processing is a promising technology to develop porous, resorbable polymer constructs with structural and mechanical properties similar to human bone.