Supercritical carbon dioxide-processed resorbable polymer nanocomposites for bone graft substitute applications

SUPERCRITICAL CARBON DIOXIDE-PROCESSED RESORBABLE POLYMERNANOCOMPOSITES FOR BONE GRAFT SUBSTITUTE APPLICATIONSbyKEVIN C. BAKERAugust 2011Advisor: Rangaramanujam M. Kannan, Ph.D.Major: Biomedical EngineeringDegree: Doctor of PhilosophyNumerous clinical situations necessitate the use of bone graft materials to enhance boneformation. While autologous and allogenic materials are considered the gold standards in thesetting of fracture healing and spine fusion, their disadvantages, which include donor sitemorbidity and finite supply have stimulated research and development of novel bone graftsubstitute materials. Among the most promising candidate materials are resorbable polymers,composed of lactic and/or glycolic acid. While the characteristics of these materials, such aspredictable degradation kinetics and biocompatibility, make them an excellent choice for bonegraft substitute applications, they lack mechanical strength when synthesized with the requisiteporous morphology. As such, porous resorbable polymers are often reinforced with fillermaterials. In the presented work, we describe the use of supercritical carbon dioxide (scCO2)processing to create porous resorbable polymeric constructs reinforced by nanostructured, organically modified Montmorillonite clay (nanoclay). scCO2 processing simultaneouslydisperses the nanoclay throughout the polymeric matrix, while imparting a porous morphology tothe construct conducive to facilitating cellular infiltration and neoangiogenesis, which arenecessary components of bone growth. With the addition of as little as 2.5wt% of nanoclay, thecompressive strength of the constructs nearly doubles putting them on par with human cortico-