| OBJECTIVE: It is common to be met in orthopedic clinic that the bone defects haven't ideal methods to repair at present.Scientist seek a kind of perfect and artificial bone substitute for repair of bone defects in long times, but the effect is not perfect. The aim of the present experiment is to prepare the composite material of decalcified bone matrix(DBM) impregnated calcium phosphate cement(CPC) with recombinant human bone morphogenetic protein-2(rhBMP-2), to analyze the mechanical, microstructure and biocompatibility properties of composite material, and to investigate the best component proportion of this compositions. More of the present experiment is to study the ultramicrostructure, radiographic and histological properties of composition implanted in bone defect, to evaluate the efficacy of the composite materials in healing of the bone segmental defect of long bone and to analyze the biodegradable properties for the use in clinic and the batch of production.METHODS:(1) The rabbit DBM were prepared beforehand. The rhBMP-2 and DBM were mixed with adsorption. The mixture was added into CPC material at the proportion of DBM weight being 0.1, 0.2, 0.3, 0.4, 0.5, 0.6and 0.7, with the proportion of rhBMP-2 being 1.2×106 mg/ m3. (2) With the proportion of DBM being 0.1, 0.2, 0.3 and 0.4, the composition were solidified and examined by biomechanics and scanning electron microscope(SEM).The mechanical and microstructure properties of composite material were analyzed for investigating the best component proportion of the compositions. (3) By study of systemic reaction of animals'body for implanting the composition, the biocompatibility was evaluated. By exvivio test of haemocytolysis, pyrogen reaction and disturbance of blood coagulation was caused by implants, the biocompatibility was analyzed. The biocompatibility was verified by view of adverse cellular reactions in the interface region between implants and muscle. (4) Rabbits underwent femur condyles osteotomies with creation of a 0.5 cm cylindrical defect and the defect was filled with implants of composite material with the proportion of DBM being 0.2.They were killed at 6,12 or 24 weeks, regenerated bone was studied by scanning electron microscope and histology. (5) Rabbits underwent osteotomies with creation of a 1.5 cm radial defect and a 0.5 cm femur condyles defect. The defect was filled with cylindrical implants of composite material with the proportion of DBM being 0.2 or 0.3. The efficacy of the composition in healing of the bone segmental defect of long bone was valuated by radiographic evaluation and histology. The biodegradable property of the composition was studied by radiographic evaluation and ultramicrostructure properties.RESULTS: (1) There were many irregular gaps of more than 100μm in the composite materials, when the proportion of DBM was from 0.2 to 0.4. Most of gaps'diameters were less than 100μm when the proportion of DBM was no more than 0.1. The DBM and CPC couldn't be consolidated when the proportion of DBM was no less than 0.5. The compressive strength of the compositions was progressively decreased, in accordance with the increase of proportions of DBM. With the proportion of DBM being 0.1, 0.2, 0.3 and 0.4, the ultimate compressive strength was (8.12±0.79), (5.46±1.13), (5.13±1.18), (1.49±0.61). A significant difference (P<0.05) was found in the statistical comparison of the different groups with regard to the composition's ultimate compressive strength, except between 0.2 and 0.3. But the mean value of human cancellous bone's compressive strength was strikingly higher than 1.493 MPa. (2) The composition has a perfect biodegradable property. (3) At 6 weeks after femur condyles osteotomies, a significant difference in the interface region between implants and bone was not viewed by histology and scanning electron microscope. It was viewed by histology and scanning electron microscope that the interface region between implants and bone was filled with osteoid substance with colonization inside the materials by new bone formed. At 12 weeks, Histology showed formation of blood vessel and osteoblasts inside the materials. At 24 weeks, the defect in femur condyles were almost completely repaired by bone tissues, most of implants was resorbed and replaced by new bone. (4) At 6 weeks after radial osteotomies, a significant difference in the interface region between implants and bone was not observed on radiographs. Radiographs displayed new bone formation around the implants. At 12 weeks, radiographs showed an increase of new bone amount around implants. The interface region was not seen, on radiographs, and the profile of implants was changed with absorption of materials particle. At 24 weeks, radiographs showed the resorption amount of implants are increase and the uniformly radiopaque segment filled with implants became partly radioparent. At 36 weeks, radiographs showed that most of implants were replaced by the bone tissues and the radiopaque segment almostly became radioparent. The study by histology supported a coincident conclusion. From 6 to 24weeks, in femur condyles osteotomies group, radiographs showed that with absorption of materials particle, the significant decrease in the size and density of implants. The same things were observed by scanning electron microscope.Conclusions: Along with the increase of proportions of DBM, the porosity of compositions is more plenty, contrarily the compressive strength of compositions is descended accordingly. Compositions with DBM proportion of 0.2 ~ 0.3 could be used in repairing cancellous bone's gap where do need to bear lower load. The composition has a perfect biodegradable property. The composite materials implanted in bone segment defect can stimulate the growth of osteoblast, blood vessel and new bones. The materials can be replaced by autogenous bone for its biodegradable property.
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