Image-guided modeling, fabrication and micromechanical analysis of bone and heterogeneous structure

This research has developed a novel image-based modeling approach and a direct fabrication technique for design and manufacturing of multi-scale, custom designed bone scaffolds and replacements. The developed modeling approaches take into consideration the morphological randomness of trabecular bone and its effect on macroscopic mechanical behavior. The study has also developed a homogenization computational algorithm for characterization of heterogeneous tissue scaffolds and composite structures. The new modeling approach and the direct fabrication method will facilitate new therapeutic development in tissue engineering. Specifically, three statistical voxel models were developed in this study. By incorporating a random-descriptor, i.e., two-point correlation function, an image-guided close-cell voxel model was developed first and applied to model a high-density ewe vertebral trabecular bone structure. The second model is a statistical open-cell voxel model applied for representing low density human vertebral trabecular bone by introducing a randomness index to consider the randomness of the trabecular architecture. The third model is a multi-scale voxel model for representing both micro-architecture and macro-anatomy of vertebral bone structure. This multiscale modeling approach can be applied to design, model and fabricate new generation of tissue scaffolds and replacements, particularly for scaffolds with patient-specific customized anatomy. Integrating with the voxel model, a direct fabrication process based on the ink-jet freeform fabrication technology was developed. Since the voxel model is a natural sliced mode, the model can be directly used to generate the machine toolpathes without being sliced. Using the ink-jet printing technique, each voxel located on the two dimensional layer of the voxel model will all be processed according to their voxel or droplet status. Three dimensional object can then be built layer-by-layer. This study also developed a computer aided characterization approach to evaluate the effective mechanical properties of the heterogeneous structures, The process of computer-aided characterization and its interface with design model, the development of computational algorithm for finite element implementation and the numerical solution of asymptotic homogenization theory were presented. Applications of the algorithm to characterize the effective mechanical properties of porous tissue scaffold and the electric magnetic comosite conductors were presented. Good agreements between the model predictions and the available analytical and experimental data were achieved.