| It would be beneficial to develop scaffolds with oriented microstructure and controllable architecture to fulfill the different needs in bone repaire and replacement application. The natural bone was demonstrated to be biologically active. It is therefore of great significance to obtain porous bio-ceramics with anisotropic structure and piezoelectric property with fine design and controllable preparation method. Freeze casting was utilized to prepare porous HA/BaTiO3composite with oriented architecture in this thesis. The effects of rheological properties of aqueous suspensions and the freezing condition on the porous characteristics of freeze-east ceramics were systematically discussed. The fine control of the final microstructures and the corresponding properties were realized. The piezoelectric effect was introduced to the porous bio-ceramics successfully. The main results were shown as below:1. The mechanism of the microstructure evolution of porous HA ceramic was studied. The employment of the near nano-sized powder was proven to be unfavourable to obtain the dense lamellar ceramic wall. A homogeneous structure with desirable orientation in the sintered samples can be achieved by the suspensions with the addition of1wt.%dispersant. There was no need to adjust the pH value of HA suspension in this experiment, as the initial suspension showed a well dispersed state. The addition of1wt.%binder can resulted in integral and dense porous structure. Long-range ordered oriented porous structures can be obtained by the utilization of the double-sided cooling set-up. With the increase of the cooling rate, the lamellar spacing and the thickness of the ceramic wall decreased and increased respectively.2. With the employment of different volume fractions and particle sizes of HA and BT powders, the control of morphologies and the corresponding properties were investigated. Porous HA10/BT90composite exhibited the higher d33value than that of the natural bone with the thickest, densest lamellar ceramic wall and the best parallelism among HA10/BT90, HA30/BT70and HA50/BT50. Long-range ordered microstructure, dense ceramic wall and no large defect can be obtained in the1HA/0.29BT and0.2HA/1.49BT samples. With the increase of the solid loading and cooling rate, the lamellar spacing and the thickness of the ceramic wall of both types of1HA/0.29BT and0.2HA/1.49BT samples decreased and increased, respectively, which exhibiting the dentritic and smooth details respectively. The increase of the solid loading and cooling rate resulted in the high compressive strength and the piezoelectric coefficient, but the low porosity. By combining gel casting with freeze casting, not only the lamellar porous structure, but also the large quantities of adhesion and circle/elliptical pore channel resulting from the polymer template can be achieved.3. MTT cytotoxicity results demonstrated that porous HA/BT composites prepared by freeze casting did not present any cytotoxic effect to L929cells. The influence of porous HA10/BT90ceramics with different porosities on the adhesion, proliferation and differentiation of the MG-63osteoblast cells were investigated. The results showed that the lamellar structures were favorable to proliferation and differentiation of the MG-63osteoblast cells, and porous HA10/BT90ceramics with50%porosity had the most obvious active effect on the proliferation and differentiation processes. Porous HA10/BT90ceramics after poling but without being applied load exhibited little effect on adhesion, proliferation and differentiation processes. Future work should focus on the comparative in-vitro experiments with and without the load applied to the porous composite, and animal experiments will also be carried out to further evaluate the growth behavior between the implant and the host.In summary, porous HA/BT composite with oriented pore structure prepared by freeze casting will guide the way to the preparation and application of the porous ceramic scaffold which can be used in bone tissue engineering, and provide a implementation approach and reliable technical support for the biomedical scaffold. |
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