Preparation And Biological Properties Of Macroporous Calcium Phosphate Scaffolds Used For Filling Bone Defects

Artificial bones with high porosity, high specific surface area and interconnected pore structures made it possible that materials connected biologidcal cells well and provided space for bone tissue to grow. Different routes have been utilized for preparation of porous calcium phosphate including cement self-setting, microsphere close-packed and coating organic foams. The relationship between factor of porosity and aperture of porous body and its biological properties were studied in this paper. Macroporous calcium phosphate biomaterials based on α-tricalcium phosphate (α-TCP) with porous structures suitable for implantation purposes were prepared in this work. A new ''self-setting'' technique that uses gelatin granules as consolidator agent and as pore formers, enabled us to tailor the porous biomaterials for the intended application. Pore sizes as large as 200～400μm micrometers could be generated by adjust the swelling behaviour of gelatin according to the pH. Chitosan microspheres were stacked in a polymer mould according to the close-packed cubic structure to form a porous mesh like preformed body with a void volume of at least 26%. The preformed body was impregnated with ceramic slurry of a calcium phosphate-based compound, and then dried to obtain a green compact. The compact was calcined at 600°C and sintered at 1200°C to form porous calcium phosphate biomaterials. The porous bodies by this technique were found to have tractable and interconnected pores in the range of 60～70%, The porous β-TCP with average porosity of 85% and good connectivity was prepared by coating organic foams, the diameter of the macropores is between 100 and 500μm, while that of the micropores is below 5μm, and the materials join on its neck. Porous β-tricalcium phosphate (β-TCP) scaffolds prepared by coating organic foams were applied in biological experiments. The results showed that the cvtotoxicity of the scaffold always maintained in the grade of 0～1, which indicated that the cvtotoxicity of the scaffold was not obvious. The cells of the scaffold grew normally in accordance with close-packed rule in the form of antenna or scalene triangle. The rats of the scaffold were in good condition in acute systemic toxicity test, which didn't react to the toxicity expect for the increment of body weight. In 72h observation period, the rats acted normally, ate and drank well and none died. The hemolysis percentage of the scaffold was 2.4%. According to the criterion of the hemolysis percentage less than 5% advanced in the properties tests of medical biological materials in indirect blood contact, extrasomatic experiments didn't arouse hemolytic reaction and it met the need of application in medical biological materials. Rabbit osteoblasts were performed on the substrates of the porous scaffolds. The experimental results indicated that the amount of the alkaline phosphatase and the osteocalcin increased with the culture time extending, suggesting a good contacting of osteoblasts with scaffold materials.