Study of osteogenic properties of recombinant human bone morphogenetic protein-2 loaded α-hemihydrate calcium sulfate/nano-hydroxyapatite combined bone materials

English Keywords:Recombinant human bone morphogenetic protein-2  α-calcium sulfate hemihydrate  Nano-hydroxyapatite  Thoracolumbar fracture  Minimally invasive of surgery  Sheep

English Abstract:

  【Abstract】 Objectives: To evaluate osteogenic properties of recombinant human bone morphogenetic protein-2(rhBMP-2) loaded novel α-hemihydrate calcium sulfate/nano-hydroxyapatite(α-CSH/nHA) combined bone materials. Methods: Injectable α-CSH/nHA/rhBMP-2 composites had been developed first, then 6 hole defects with 6.0mm in diameter and 15.0mm in depth were experimentally created in left pedicles of L1-L6 lumbar vertebrae in 12 adult sheep. Defects of the first sheep were randomly divided into three groups, and which was the standard of subsequent 11 sheep. The experimental group(L2, L5) was filled with α-CSH/nHA/rh-BMP-2 composites, control group(L1, L4) with injectable calcium phosphate cement(CPC), blank group(L3, L6) with none material. After 4, 8 and 12 weeks, four animals were sacrificed and 24 vertebral specimens were taken respectively, then the followings were made respectively: X-ray and micro-CT imaging for observation of repairing, and biomechanical examination for testing compression strength and compression modulus, as well as histological evaluation by comparing new bone formation rate. Results: Biomechanical results illustrated that after 4 weeks, the difference of compression strength and compression modulus between experimental group and control group was not significant(P>0.05), and both significantly higher than the blank group(P<0.05); after 8 or 12 weeks, they were also much higher than the blank group(P<0.05), the compression strength and compression modulus of experimental group were higher than those of control group(P<0.05). Radiographic and histological results indicated that after 4 weeks, the vast majority composites of the experimental group had yet degraded, the density was slightly lower than that of normal bone, and a large number of short and not-yet-shaping new bone trabeculae were found surrounded by many osteoblasts; the defect was full of high density CPC material in control group, with no obvious sign of degradation, the bone-material boundary was obvious, and a small amount of immature bone formatted at the edge of the defect; while the defect of blank group was large with neat edge, where the new bone formation was barely. At 8 weeks after operation, the degradation of combined materials in experimental was apparently complete, the new bone trabeculae within the defect became larger, thicker and longer, and started early shaping; in control group, CPC began to degrade partially, new bone formation was shown at the edge and central degradation area, which was less than that of the experimental group; on the contrary, the defect healing of blank group was not obvious, there was few new bone trabeculae at the edge. After 12 weeks, the defect of experimental group was completely filled with maturing new bone trabeculae, in which the structure and density were almost as the same as normal bone trabeculae, it was difficult to distinguish the defect area from normal site; while CPC was substantially degraded in control group, remaining only a small lump and some sporadic materials, and defect restoration was obvious at the edge, new bone trabeculae grew into the residual material, which were divided into series of island-like pieces; defects in blank group were still large, presented as clearly visible low density, with very little new bone formation. Conclusions: The α-CSH/ nHA/rhBMP-2 composite is a promising bone repair material for minimally invasive surgery, which performs outstanding osteogenic properties in vertebral defect of sheep.