Injectable RhBMP-2/silk Fibroin/calcium Sulfate Cement In Healing Osteopenic Goats Vertebral Bone Defects

Objective: To evaluate the repair capacity and characteristics of rh BMP-2/silk fibroin /calcium sulfate(rh BMP-2/SF/CS)cement in healing osteopenic goats vertebral bone defects.Methods: Twelve osteopenic goat models were made and a 4mm diameter cylindrical bone defect was made on goat lumbar vertebrae by surgery.The rh BMP-2/SF/CS bone cement was prepared as experimental group,the SF/CS bone cement and polymethylmethacrylate(PMMA)bone cement were used as a control groups.Three groups of bone cement materials were randomly filled into three lumbar vertebral bone defects.Another one vertebral bone defect was preserved without cement as a blank control group,and a vertebral body without bone defect was retained as a normal control group.Four goats were sacrificed each time at 4 weeks,8 weeks and 12 weeks postoperatively.Vertebrae samples were taken for X-ray densitometry,biomechanical testing,Micro-CT scan,and histological examination.Results: The X-ray densitometry showed no significant difference in X-ray density between different bone cement groups and at different time points(P>0.05).Biomechanical tests showed that the vertebral body strength of normal control group and SF/CS group showed a slowly decreasing trend.At 4 weeks postoperatively,the vertebral body strength of SF/CS group and rh BMP-2/SF/CS group were similar to that of normal control group,lower than that of PMMA group.The strength of rh BMP-2/SF/CS group got a peak at 8 weeks postoperatively and was higher than other groups except PMMA group.The strength of PMMA group was higher than that of other groups at all time points,and the blank control group was lower than that of other groups.The vertebral bodies' stiffness in all groups showed an upward trend.The stiffness of rh BMP-2/SF/CS group was higher than that of normal control group at 8 weeks postoperatively.Micro-CT scan showed that SF/CS and rh BMP-2/SF/CS were completely degraded at 4 weeks postoperatively,and a small amount of bone trabecular hyperplasia was observed around the bone defect in rh BMP-2/SF/CS and SF/CS groups.At 8 weeks after the operation,the trabecular hyperplasia was observed in the rh BMP-2/SF/CS group and a small amount of trabecular hyperplasia was observed in the SF/CS group.At 12 weeks after surgery,the rh BMP-2/SF/CS fractures nearly healed,and irregular trabecular bone hyperplasia was observed in the SF/CS group and blank control group.In the PMMA group,only a small amount of new bone around the drill hole was observed at 12 weeks postoperatively.The vertebral specimens' histological examination showed that SF/CS group and rh BMP-2/SF/CS promoted the trabecular bone growth,and the trabecular area of SF/CS group and rh BMP-2/SF/CS group were similar to that of normal control group,higher than that of the blank control group and PMMA group at 8 weeks postoperatively.SF/CS cement and rh BMP-2/SF/CS cement promoted the proliferation of collagen in trabecular bone,at 8 weeks and 12 weeks after the operation.The fluorescence microscopy showed that new trabecula bone was formed at the 4th week postoperatively in the rh BMP-2/SF/CS group,at 8th week postoperatively in the SF/CS group,and at 12 th week postoperatively in the blank control group.No fluorescence enhancement was observed in the PMMA group and the normal control group.Conclusion: 1.The rh BMP-2/SF/CS cement and SF/CS cement show osteoinduction in osteopenic goat vertebral bone defect models,which can provide a good environment for fracture healing,accelerate fracture healing,and increase vertebral body strength.Compared with SF/CS cement,the rh BMP-2/SF/CS cement has better osteoinductive properties.2.The rh BMP-2/SF/CS cement and SF/CS cement are completely degraded within 4 weeks in the goat vertebral body,which is faster than the growth of new bone in the vertebral body.Its ability to improve the strength and stiffness of the vertebral body is mainly achieved by optimizing the local osteogenic environment and accelerating the growth of trabecular bone.Improving the degradation time of rh BMP-2/SF/CS cement is expected to further enhance its osteogenic capacity.