| Large skeletal repair is always a tough problem perplexing surgeons. The bone graft substitutes play an important role in repairing bone defects, so the search for ideal bone graft substitute to repair bone defects is always an important subject in orthopaedics. Calcium Phosphate Cements (CPC), or named Hydroxyapatite (HA), was a novel and superior bioactive material for bone repair. The superiority lay in that CPC had some unique properties which common materials such as PMMA did not have as well as all properties necessary for implanted materials, these unique properties included being able to be molded at will, sustained releasing of drug and tight interface.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. But an ideal carrier or delivery system was absolutely necessary otherwise BMP could not exert its osteoinductive activity. In this study, following the principle of tissue engineering, we planed to compound bovine BMP (bBMP) with CPC to make a plastic bioactive artificial bone with both osteoinduction and osteoconduction activities. For studying its feasibility in clinical practice, the following three experiments had been undertaken. 1. Study on the influence of bBMP on properties of CPCThe bBMP-loaded CPC was synthesised with CPC and bBMP in the certain ratio of CPC powder to bBMP. We studied the properties of CPC and bBMP-loaded CPC, including the setting time, compressive strength, the setting products and micro-structural development. The properties of thematerial were evaluated by setting-time test, biomechanics testing instrument, XRD and SEM. Result showed that there was no significant difference in both CPC and bBMP-loaded CPC in the setting time, compressive strength , the setting products and microstructural development(P>0. 05). It can be concluded that the introduction of the bBMP had no effect on the CPC's applied properties and setting products.2. Ectopic osteoinduction of PBABCPC and PBAB samples were separately into the thigh muscle pouches of mice. Samples in different time were tested by histological analysis and alkaine phosphatase (ALP) measurement to observe the induced ectopic bone formation.. Histological study showed that no new formed cartilage or bone was found in CPC group. In the PBAB group, the proliferating mesenchymal cell and abundant cartilage were found in 1 week. Cartilage is gradually coverting into woven bone at 2 weeks, Lamellar bone appeared at 4 weeks. At 6 weeks, the presence of newly formed bone was observed. Mature lamellar bone with bone marrow appeared at 8 weeks. PBAB is partly absorbed and replaced by newly formed bone and bone marrow. The results of ALP changes in accord with newly formed bone. 2 weeks after implantation, the ALP increased evidently in PBAB groups and reached the highest level at the sixth week, which was about 166U/1. It can be concluded that PBAB had good potentiality of ectopic bone induction.3. Effect of PBAB in repairing segmental defects of radius in rabbitsIn order to study the ability of bBMP-CPC composited bone substitute (PBAB) in the treatment of bone defect of long bone, we implanted PBAB samples into segmental bony defects of rabbit's radius. 15mm-defect nonunion models were established in the middle of bilateral radial diaphysis in 30 rabbits. In 2w, 8w, 24w groups, we selected randomly tworadius's bony defects as control group which were kept untreated. The others were treated with implantation of CPC or PBAB. To evaluate the effect of artificial bone substitute in repairing segmental bone defects, the osteogenesis of the bone in the defect area and degradation of PBAB and CPC was observed by X-ray , histomorphology and mechanical measurement at the end of 2, 4, 8, 16 and 24 week after operation. New bone formation was observed to be increasing significantly in PBAB with the passage of time. By the end of 24 weeks, the bone defects treated with PBAB had been healed. No healing was fo... |
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