Optimization of the structure of three-dimensional interconnected porous carbonate apatite bone grafts with spherical granules.

A block-type of three-dimensional carbonate apatite bone graft (3D-CO₃Ap) is demanded for applying large bone defects. Although we fabricated the 3D-CO₃Ap with high mechanical strength by fusing polymer-bound spherical precursor, the optimized condition has not yet been found. In this study, we indicated the optimized condition for 3D-CO₃Ap by controlling granular packing ratio (i.e., different compression ratios of the mold volume from 100% to 140%). 3D-CO₃Ap was obtained in the condition from 110% to 130%, even though the block was collapsed in 100% and complete conversion to CO₃Ap was not achieved in 140%. The highest compressive strength was achieved with 130% 3D-CO₃Ap because the intergranular connection area was the most enhanced. Furthermore, when reconstructing bone defects, 130% 3D-CO₃Ap prevented soft tissue penetration and showed good osteoconductivity because of their controlled intergranular pore size. The 130% compression was optimal for achieving both high mechanical strength and osteoconductivity.