(601g) Supercritical Carbon Dioxide Processed PDLA Nanocomposite Foams as Resorbable Bone Graft Substitutes

Autogenous bone (autograft) is the current standard method to achieve arthrodesis and bone fracture union, however complication rates as high as 30% have been associated with the harvest procedure. Many different types of synthetic constructs have been proposed and investigated as possible replacements for the current methods, however most suffer from significant limitations in mechanical properties and biocompatibility or display high infection risk due to non resorbability. In this study, supercritical CO₂ processing has been used to synthesize porous, resorbable, poly-D-lactic acid (PDLA) scaffolds with dispersed organically modified montmorillonite nanoclay and pore morphology, compressive properties and biocompatibility were evaluated.

The porous morphology of the nanocomposite foams produced indicates suitability for use as a scaffold for bone growth^[1]. Both pure PDLA and PDLA-nanocomposite constructs synthesized for this study exhibited average pore diameters of approximately 240nm, which is in the range determined to be sufficient to support neovascularization and cellular infiltration, and pores show a high level of interconnectivity which is necessary for proper nutrient transport. The mechanical properties of the porous nanocomposite scaffolds compare favorably to other synthetic polymer constructs, and are significantly higher than the properties of pure PDLA scaffolds. The scCO₂ process used to produce the porous nature of the materials has also previously been shown to be effective for producing clay dispersion in polymer melts, resulting in significantly enhanced properties.

The biocompatibility of the constructs, as determined by the alkaline phosphatase activity of cultured osteoblasts, was greater than the polystyrene culture plate controls. Addition of nanoclays to resorbable polymer matrices seems to have no significant effect on the differentiation of pre-osteoblast cells, as measured by production of alkaline phosphatase. Ostoeblast extracellular matrix deposition on the nanocomposite constructs also indicates favorable biological interaction. Calcium phosphate-rich deposits could clearly be seen on the surface of the constructs, as well as within pores. This deposition was observed to also occur at the very center of the cultured constructs, which indicates that osteoblasts are able to penetrate the porous network of the nanocomposite constructs.

1. Baker, KC, R. Bellair, M. Manitiu, HN Herkowitz, RM Kannan, Journal of Mechanical Behavior of Biomedical Materials (2008) in press