ABSTRACT Tissue Engineered Composite Bone Cement For Reinforcing Osteoporotic Bone Matthew Wettergreen, Michael A.K. Liebschner Department of Bioengineering, Rice University, Houston, TX INTRODUCTION: Injectable materials for use in vertebroblasty and kyphoplasty have been augmented with micro- or nano- sized particles to increase the overall mechanical strength of the composite material. These studies have focused solely on the improvement of the mechanical properties through the adjustment of geometry, architecture, and degradation profile of the material. The goal of the current study was the generation of a porous material, with a controlled rate of degradation, which can be used for injection purposes. MATERIALS AND METHODS: By focusing on the engineering of an interconnected pore structure, a high surface area to volume ratio can be created, increasing the strength of the material while maintaining porosity. A novel injectable bone cement is created using a Calcium Phosphate slurry with solid phase polypropylene fumarate (PPF) particulates of engineered architecture. The PPF is formed into macrosize (~750um) two-dimensional star-like shapes using rapid prototyping technology and molding processes. The star shape is designed to seal the spaces between adjacent trabeculae, which have a spacing of approximately 1mm. Plugging of the inter-trabecular spacing should aid in the containment of the liquid bone cement during injection, preventing the common problem of overfilling. RESULTS AND CONCLUSION: The optimal volume percent and +/-10% volume percent of PPF is introduced into the viscous material to create the injectable composite. The three formulations are then injected into cylindrical volumes for testing purposes. After curing, the samples are scanned on a µCT 80 (Scanco Medical, Basserdorf, Switzerland) with a resolution of 10um. Incorporation of a contrast agent will allow the visualization of each phase of the composite material using µCT. The scans will be used to evaluate the interconnected void spaces formed when the PPF degrades. A degradation study is performed to evaluate the degradation of the PPF micro-particles. Degraded samples will be mechanically tested to evaluate whether degradation of the microparticles reduces the mechanical strength of the cements to levels insufficient for usage in vertebroblasty and kyphoplasty. By using a composite material consisting of a liquid element phase, an ordered pore structure can be generated. The cured material may promote bone growth and could ultimately improve the biomechanical quality of the regenerated trabecular bone in a vertebral body after treatment. The incorporation of geometric shapes and regulated architecture into liquid injectable materials could be used in vertebroblasty and kyphoplasty for reinforcement or bone fracture repair.

1. Tissue Engineering Composite Bone Cement for Reinforcing Osteoporotic Bone Matthew A Wettergreen, Antonios G Mikos, Michael AK Liebschner

8. Generation of Y-Shapes 0.98 0.39 0.29 0.33 0.45 Avg. Volume = 0.221 mm 3 Avg. Volume = 0.221 mm 3 Bounding box = 1.0mm x 1.5mm Surface Area = 2.895 mm 2 Surface Area = 2.196 mm 2 Bounding box = 0.60mm x 0.60mm All dimensions in mm 0.50 - 0.71

9. Building of 3-D architecture Fused Deposition Modeling Material Reservoir Piezo 1 mm y z

20. Thank You