Fabrication of Interconnected Porous CaCO₃ From Gypsum

Objectives: Marine coral used in clinics as bone substitute has interconnected porous structure and its composition is calcium carbonate (CaCO₃). Unfortunately, marine coral is not pure calcium carbonate but contains other elements. In this study, therefore, interconnected porous CaCO₃ was to fabricated from gypsum and evaluate its tissue response.
Methods: Calcium sulfate hemihydrate (CSH) was mixed with 10mass% nylon fibe, then mixed with water with water/CSH ratio of 0.2. After set, the set CSH with the fiber was heated up to 700°C to burn out the fiber. Thus obtained calcium sulfate anhydrous (CSA) was immersed in Na₂CO₃ solution to convert composition of CSA to CaCO₃ maintaining the interconnected porous structure. Morphology of the interconnected porous CSA and CaCO₃ was observed by SEM. Compositional analysis was made by XRD. The tissue response to interconnected porous CaCO₃ was evaluated by reconstructing the cranial bone defect of rabbit, and examined with m-CT and histologically one month after implantation.
Results: When CSH paste containing nylon fiber was heated at 700°C for 3 hours, nylon fiber was burned out and interconnected porous structure was fabricated. XRD analysis confirmed its composition as CSA. No structural change was observed even when interconnected porous CSA was immersed in 1mol/L Na₂CO₃ solution for 24h. However, XRD analysis revealed that the composition was CaCO₃. No inflammatory response was observed during the implantation period. The m-CT revealed that the bone defect was reconstructed with the interconnected porous CaCO₃ and newly formed bone. Histological evaluation revealed that new bone was formed not only surface of the porous CaCO₃ but also interior to the porous CaCO₃.
Conclusions: Interconnected porous CaCO₃ was found to be fabricated using CSH as a precursor and showed good potential value to be ideal bone substitutes.