| Objective:Using of poly - D,L-lactic acid(PDLLA) andβ-calcium phosphate(β-TCP) on different scales product 6%β-TCP / PDLLA,12%β-TCP / PDLLA and pure PDLLA three kinds of materials which can be absorbed.Manufacture Centrum-vertebra fracture repairing absorbable supporting plugger,(CASP) andΦ4 mm,the 5 mm long cylindrical material specimen.New Zealand white rabbits were implanted in gluteal muscle and the femoral condyle.Three kinds of materials in the course of degradation in appearance,the shape changes,the tissue surrounding materials compatibility,the rate of mass loss,the imaging changes,the surface changes in electron microscopy and so on at middle-time and long-term after implanted.The purpose is to evaluate materials' degradation products' security,degradation rate,biomechanical properties after implanted.Then select the material which more suitable for further study and clinical applications.Methods:120 New Zealand white rabbits.2.5±0.3kg,were randomly divided into three groups,namely 6%β-TCP / PDLLA group.12%β-TCP / PDLLA group,PDLLA group,each 40.CASP and cylindrical were weight by electronic materials weighing scales,records for the original quality.CASP and cylindrical materials sample were implanted into New Zealand white rabbits' bilateral gluteus muscle and the femoral condyle.Take a general observation after experiments on animals.6,9.12.15 and 18 months after operation,experimental animals were killed after been examined by X-ray,to observe the material surrounding muscle tissue femoral condyle and whether to change in shapes.Remove muscle specimens,released from the attachment organizations to observe the appearance of materials,patterns change.Materials will be weighing again after cleaned,dried,calculating the loss of quality(n = 8).Materials in muscle and bone were removed to examine by histology.Evaluate the different materials from those effects up to eighteen months' in degradation security,the course and the rate of degradation.And filter a material which more suitable for clinical application.Result:All experimented animals were contributed to analysis.1.All of three group of animas were good in general after implantation of CASPs and cylindrical materials.The day after operation,animals sober and started drinking water,started eating the next day,the wound I / A healing,removing the thread after two weeks.No purulent infection,no skin effusion.In the longest period of eighteen months of observation time.three combined materials were absorbed completely in visible,distal femur no swelling,necrosis,without osteoporosis,muscles around the material no fibrosis,infection,necrosis,liquefied phenomenon.2.Six months.6%β-TCP / PDLLA group's CASP was white,edges became blunt,surface was roughly,no degraded particles in vision;12%β-TCP / PDLLA group's CASP was degraded to white particles,been packaged by fiber capsule; PDLLA group's was ivory',transparency weakened,edges became blunt,packaged tightly by surrounding tissue.There are no infection,swelling and exudation around three kinds of models.Nine months.6%β-TCP / PDLLA groups' were smaller and deformation,surface became roughly,pits were insight;12%β-TCP/PDLLA groups" volume became further smaller,particles were different in size after degradation,fiber capsule was thinner,was not easy to separation;PDLLA groups' became colloid,no shapes,packaged tightly by surrounding tissue,fiber capsule was thinner.There are no infection,swelling and exudation around three kinds of models.Twelve months, 6%β-TCP / PDLLA group's CASP was became further smaller,white particles were visible,fiber capsule's wall was thinner,packaged tightly by surrounding tissue;12%β-TCP / PDLLA groups' became white particles and were lower in quantity obviously, the capsule was not completely,arounding tissue was osteoporosis and pale yellow; pure PDLLA groups' degradation material was ivory,fiber capsule was completely, but osteoporosis.There are no infection,swelling and exudation around three kinds of models.Fifteen months,6%β-TCP / PDLLA groups' CASP were degraded to pale yellow particles,been absorbed mostly,fiber capsule was not completely;12%β-TCP / PDLLA groups' had pale yellow pigment in muscle only;purely PDLLA CASP became one or two white particle had not been absorbed in muscle,arounding tissue was osteoporosis.There are no infection,swelling and exudation around three kinds of models.Eighteen months,three kinds of models were absorbed absolutely,no degradation materials in vision,arounding tissue was normally.Femoral condyle where three kinds of materials implanted were covered by bone tissue at six months after operation,no infection,swelling and exudation.There no abnormal phenomenon in latterly.3.Six months after implanted,6%β-TCP / PDLLA groups' weight loss was about 8.896±1.194%,PDLLA groups' was 25.590±2.821%there are a significant difference between two kinds of models(P<0.05).12%β-TCP / PDLLA groups' could not been weighted because materials had been degraded into particles and could not been removed completely.Nine months.6%β-TCP / PDLLA groups' weight loss was about 31.515±1.337%,PDLLA groups' became colloid and been wrapped tightly could not been weighted.Twelve months,three kinds of models could not been weighted.4.X-ray check:After implanted 6 months.6%β-TCP / PDLLA CASP is not clear,the surface porous disappeared basically,the size became smaller than 3 months, but the profile could be identified,12%β-TCP / PDLLA CASP is not easy to identify on film,the image is faintly.The femoral condyle where two kinds of material had implanted not been dissolved.After nine months that 6%β-TCP / PDLLA material image is fuzzy,the image is faintly,12%β-TCP / PDLLA material could not been found on film.The femoral condyle where two kinds of material had implanted not been dissolved.After 12 months andl5 months,there no materials' image on X-ray films,no signs to identify bone dissolved.5.Electron microscope scanning of 6%TCP/PDLLA cylindrical material.That was smooth,regulation and no gap on surface.Eight weeks after implantation,gaps and hole was visible on material surface;after 16 weeks,more leakage is visible on material surface and deep layer has more wormhole-like holes;after 24 weeks,gaps were more,wider and irregular;after 9 months,the gaps became ditches and connected each other,there were lots of particles and density in same but difference in size.6.Observation by histology:The casp made by 6%β-TCP/PDLLA are combined tightly with adjacent tissues after implanted 6 months,fibrous capsule is completely,muscle are normally.Materials were more degraded in 9 months than 6 months,a part of striped muscle near the capsule is atrophy.Materials were more degraded and absorbed after implanted 12 months,fibrous capsule is thin,state is increased when implanted 15 months.Materials were degraded and absorbed complete almostly when implanted 18 months,fibrous capsule is incomplete and thin, adjacent muscle is normally.Every time there were no inflammatory cells in histologic observation.Within the femoral condyle,a part of 6%beta TCP/PDLLA columnar material in the six months after surgery was absorbed when new bone replacement.Tissue near the material osteoblast actively after implanted 9 months. Zone of maturing cartilage is osteoblast actively after implanted 12 months. Endochondral ossification appear calcification after implanted 12 months.Materials were degraded and absorbed completely,been replaced by normal and mature bone trabeculae,inflammatory cells were not seen each time.Conclusion:1.There are not late-occurred inflammation cause by 6%beta TCP/PDLLA and its degradation after implanted,so the material has a good biocompatibility.2.With quality loss,three materials appeared different degradation rate.but they could be degraded and absorbed completely. 3.6%β-TCP/PDLLA materials' mass loss and biomechanical decrease is more satisfactory than the others,and maybe better biodegradable composite material for thoracolumbar reconstruction.4.12%TCP/PDLLA materials' degradation rate was faster than the other two groups,so as to be a bone repair materials,it may lose supporting role to fracture site because of fast degradation in the early time after operation.5.6%%TCP/PDLLA maybe a good repairing material in orthopaedic because its degradation speed is matching with repairing of bone.
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