OBJECTIVESTo construct new type of bone graft material by combining calcium phosphate cement (CPC) with bone morphogenetic protein (BMP), and then to detect its osteogenic activity.

METHODSThe surface of CPC and CPC/BMP composite were observed by scanning electron microscope (SEM). CPC and CPC/BMP pellets were separately implanted into the thigh muscle pouches of mice. Samples obtained at different times were tested by histological analysis, SEM, organic substance detection, and alkaline phosphatase (ALP) measurement to observe the induced ectopic bone formation.

RESULTSUnder SEM, the CPC and CPC/BMP composite was found to consist primarily of platy crystals, granular crystals and some small rod-like crystals with micropores about 10-50 microm in size. BMP about 1-5 microm in size was seen like micro globules distributing evenly in the micropores. Newly formed cartilage or bone was not found in the CPC group. In the CPC/BMP group, mesenchymal cells were proliferated and abundant cartilage was found in one week. Woven bone appeared at 2 weeks. New bone formation increased with bone marrow at 4 weeks. At 8 weeks, the implanted CPC/BMP became heterogeneous and a lot of collapsed granules were observed. At the end of 16 weeks, mature lamellar bone appeared and the volume of the implanted CPC/BMP became smaller. One week after implantation, the ALP increased evidently in the CPC/BMP groups and reached the highest level at the 4th week, which was about 168 U/L. The content of organic substance in specimens increased from 22% to 39% by the end of the 16th week, showing the continuous calcification and formation of new bone. SEM also showed that the CPC/BMP composite had good potentiality of ectopic bone induction, and the new bone formed accompanied by the slow degradation of the material.

CONCLUSIONThe results of this study suggested that the CPC/BMP composite could be used as material for bone graft substitute.