| The search for ideal bone graft substitute to repair bone defects is always an important subject in orthopaedics. Bone morphogenetic protein(BMP) has good potential in treatment for bone defects as it can induce mesenchymal cells to differentiate into cartilage cells and bone cells so to form new bone. To use BMP in practice, we must combine the protein with a proper carrier as supporting medium and to release BMP slowly. Calcium phosphate cement(CPC) is a kind of non-ceramic hydroxyapatite with bioactivity developed in recent years which has been used as bone graft substitute. In this study, we synthesised a CPC and used it as BMP carrier to make a new type of bone graft substitute with both osteoinduction and osteoconduction activities. We carried out a series of studies on this composite about its physicochemical properties, biocompatibility and osteogenic activity, and made experiments of bone defects repair on animals to study its clinical application.1. Physicochemical properties of CPC/BMP compositeUnder scanning electron microscope(SEM) the CPC/BMP composite was found to consist primarily of platy crystals, granular crystals and some small rod-like crystals with micropores about 5-50 urn in size. The porosity ratio of the composite was 44.5%. BMP, about 1-5 um in size was seen like micro globules distributing evenly in the micropores. Energy dispersion analysis X-ray(EDAX) indicated the material was mainly composed of calcium, phosphor, oxygen and hydrogen, and the Ca/P ratio was 1.746. Compressive load-to-failure test showed that thecompressive strength increased rapidly after concretion and reached more than half of the limiting compression strength in 2 hours. After 24 hours of crystallization, it reached the ultimate compression strength, which was about 51 MPa. The Young's modulus indicated that the composite had better mechanical property than CPC, for the brittleness decreased after it combined with BMP. The composite had ideal solubility in phosphate buffer saline(PBS) especially in flowing test. Total calcium released from the material in 14 days in flowing test was 17 times that in static test. As a carrier for sustained releasing, the CPC can release gentamicin for about 20 days, and 91.1% of total gentamicin was released.2. Biocompatibility and biological safety evaluation of CPC/BMP compositeBiocompatibility and biological safety of CPC/BMP composite were evaluated by a series of in vitro and in vivo studies including animal experiments, cell culture, and histochemical detection to test the toxicity, pyrogen, coagulant, hemolysis and immunogen. The composite was found to have non-toxic and pyrogen-free in animal test, no hemolytic activities and it couldn't influence the blood coagulation in vitro. Implanted the composite into the muscle pouches in the thigh of mice or rabbits, it was found no obvious specific antibodies produced in serum and no significant immune reaction to foreign body. MTT detection also showed no cytotoxicity to the proliferation of cultured cells in vitro. All the results indicated that the CPC/BMP composite had good biocompatibility and was safe for clinical use.3. Ectopic osteoinduction of the CPC/BMP compositeCPC 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 alkaine phosphatase(ALP) measurement to observe the induced ectopic bone formation. No new fromed cartilage or bone was found in CPC group. In the CPC/BMP group, mesenchymal cells were observed proliferating and abundant cartilage was found in 1 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 ofcollapsed granules were observed. At the end of 16 weeks, mature lamellar bone appeared and the volume of the implanted CPC/BMP became smaller. 1 week after implantation, the ALP increased evidently in CPC/BMP groups and reache...
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