BACKGROUND: As an absorbable calcium phosphate cement and bone substitute implant, calcium phosphate stone has become the focus of bone tissue engineering research, but some deficiencies in its properties have greatly limited its clinical application. The scholars try to add some elements to modify the calcium phosphate stone, in order to enhance the mechanical properties, prolong the curing time and improve the osteogenesis.
OBJECTIVE: To make magnesium-doped brushite by adding magnesium ions to beta-tricalcium phosphate with sintering method and to detect the feasibility of magnesium-doped brushite as a bone substitute by detecting physical and chemical properties and ability of repairing bone defects.
METHODS: Magnesium-doped brushite in different molar ratios of Mg/(Mg+Ca) (0%, 6.67% and 26.67%) was prepared using sintering method. Morphological structure and compressive strength of the prepared bone cement were detected using scanning electron microscope and universal material test machine, respectively. Magnesium-doped brushite extracts (0%, 6.67%, 26.67%) were added into rabbit anticoagulant to perform a hemolytic test. Twenty-four rabbits were used to make bilateral tibial bone defect models, and then rabbit models were divided into four groups: three groups were implanted with 0%, 6.67%, and 26.67% magnesium-doped brushite bone cement, and the blank group received no treatment. X-ray examinations were performed at 4 and 8 weeks after implantation.
RESULTS AND CONCLUSION: Under the scanning electron microscopy, the 0% magnesium-doped brushite cement had a tightly packed plate-like shape and a small amount of granules with less pores; the 6.67% magnesium-doped brushite cement presented with irregular lumps and short rods; and the 26.67% magnesium-doped brushite cement was lumpy, spherical and granular. The magnesium-doped brushite cements (0%, 6.67%, 26.67%) had compressive strengths of 31.99, 26.38, 24.44 MPa, respectively. The hemolysis rate of all the brushite bone cements was less than 5%. X-ray results showed that at the 4th week after implantation, the defect margin in the blank group was ruled without new bone formation; in the 0% magnesium-doped brushite group, the bone cement was dissolved at the margin, and a few high-density shadows were detected at the junction between bone defects and the cement; in the 6.67% magnesium-doped brushite group, the bone cement was mostly dissolved and there were a large amount of new bone tissues; in the 26.67% magnesium-doped brushite group, the bone cement was dissolved at the margin, and there were high-density shadows in the center of the bone cement with less new bone formation. At 8 weeks after implantation, there were new bone deposits at the two ends of the blank group; the new bone was wedge-shaped in the 0% magnesium-doped brushite group; the bone defect in the 0% magnesium-doped brushite group was basically filled with new bone tissues, and the bone cortex was continuous; and in the 26.67% magnesium-doped brushite group, the new bone served as a bridge to link the broken bone ends with poor plasticity. These findings indicate that 6.67% magnesium-doped brushite cement has good mechanical properties and osteogenic effects.