Properties Of Calcium Phosphate Cement Modified By Starch

PartⅠ Physical properties and operability of calcium phosphate cement modified by starch【Objective】To prepare starch modified calcium phosphate cement and investigate its physical properties and operability.【Materials and Methods】There are 4groups in this part.The group of calcium phosphate cement(CPC): 90% α-TCP mixed with 10% DCPD.The group of calcium phosphate cement-Starch(CPS): 20% corn starch mixed with 80% CPC.The group of calcium phosphate cement-Starch-Ba SO4(CPB): 20% corn starch and 20% barium sulfate mixed with 60% CPC.0.25 mol /L Na2HPO4 as the liquid phase.The group of PMMA: Polymethylmethacrylate.The injectability,antiwashout,setting time,mechanical properties and microstructure of each group were measured.【Results】The injectability,antiwashout and setting time of CPB and CPS were significantly better than CPC.The setting time of CPB was appropriate.The compressive strength was in descending order: PMMA >CPB>CPS>CPC(P<0.01).We found large pores and dimples on the fractured surface of CPB exhibited more compact microstructure than the traditional CPC from SEM micrographs.There were small crystals in the CPB matrix and some fine needle-like particles in the high-magnification micrographs.These precipitates were probably HA crystals.【Conclusions】1.CPB has great injectability and antiwashout.2.The appropriate initial setting time and the final setting time give the surgeon enough and suitable operation time to complete the operation successfully.3.The compressive strength of CPB is about 46 MPa and significantly higher than CPC and CPS,but significantly lower than PMMA.PartⅡ Radiopacity,biodegradability and biocompatibility of CPB in vivo.【Objective】To investigate the possibility of application in the body by evaluating the radiopacity,biodegradability and biocompatibility of CPB in vivo.【Materials and Methods】18 Sprague-Dawley rats(9-11 weeks old,200-250 g weight)were used in the experiment.All SD rats were anesthetized by 4% chloral hydrate intraperitoneally.All specimens(CPC、CPB、CPS、PMMA)were implant into the subcutaneous pockets of SD rats.X-ray photographs of the rats were obtained at 3,7,14,28,56 and 84 days after operation and Micro-CT were obtained at 28,56 and 84 days after operation.A group of three rats were sacrificed at 3,7,14,28,56 and 84 days after implantation.The sample and tissues surrounding CPB were obtained and fixed with 10% formalin for 24 hours.Then,CPB was decalcified in 10% EDTA for 14 days,embedded in paraffin and cut by a rotary microtome.All sections were stained with HE and observed by light microscopy.【Results】All rats underwent the operation successfully and no rats died during the experiment.There were severe swelling and congestion around all specimens 3 days after implantation,but congestion cleaned and swelling subsided 7 days after implantation of CPB by naked eye.The radiopacity of CPB was as high as PMMA,and significantly higher than CPC and CPS.CPB always stayed in the same location and never moved in the subcutaneous after implantation.Micro-CT software showed that CPB could be degraded in vivo.There were 8% degradation 84 days after implantation.It was easy to found that obvious inflammatory reactions were recognized around CPB 3 days after implantation.There were few inflammatory cells can found around CPB 7 days after implantation.CPB were encapsulated in the thin and loose fibrous connective tissue 14 days after implantation.Then,the thin and loose fibrous connective tissue was substituted by the dense fibrous connective tissue.【Conclusions】1.CPB has great radiopacity.2.CPB has biodegradability in vivo.There are 8% degradation 84 days after implantation.3.CPB has good biocompatibility for temperating to the body and no adverse reactions.PartⅢ Biomechanical strength of CPB and its ability to combine with the bone in vivo.【Objective】To investigate whether CPB could enhance the vertebral body strength and its ability to combine with the bone by respectively filling CPB into the vertebral body of sheep body and the femur of rats.【Materials and Methods】88 vertebral bodies(L1-L6,2.5-3 years,weight 35-55 kg)and 15 rats SD rats(9-11 weeks old,200-250 g weight)were used in the experiment.The X-ray showed that every vertebral body has ruled out abnormalities.The disc,soft tissue and posterior element were removed.All vertebral bodies were randomly assigned to the decalcified group and the undecalcified group.The undecalcified group(48 vertebral bodies)were randomly assigned to 6 groups,then 5 groups were drilled to the sagittal plane of lumbar vertebral body by 6.0 mm diameter drill besides the control group.CPC,CPS,CPB and PMMA were filled into the previously expanded cavities.The decalcified group were fixed with 10% formalin 24 hours,and then were decalcified in 10% EDTA at 4°C for 7 days.All specimens were measured the BMD before and after decalcification.All specimens were randomly assigned to 5 groups after decalicifition.The decalcified group were also drilled to the sagittal plane of lumbar vertebral body by 6.0 mm diameter drill besides the control group.Vertebral babies with 6.0 mm diameter drill were also respectively augmented with CPC,CPS,CPB and PMMA.In order to insure uniform loading during the compression test,two endplates of every vertebral body were covered by a dental acrylic.15 rats were randomly assigned to 5 groups,including sham-operated group,control group,CPC group,CPB group and PMMA group.The femur of rats was drilled through the contralateral cortex with 2.5 mm manual electric drill by 4% chloral hydrate intraperitoneally.Then all cements which were prepared before operation were filled into the previous cavities.All rats were sacrificed after 84 days and the femur were obtained.The three-point-bending test was made by a microcomputer controlled electrical universal testing machine.The machine recorded the maximum load and the load–displacement curve.【Results】1.The undecalcified group: The biomechanical strength of the vertebral body augmented with CPB was slightly higher than the normal vertebral body and slightly lower than the vertebral body augmented with PMMA,but no statistically significant differences(P>0.01).The vertebral body augmented with CPC were fractured severely,and CPC were crumbled into powder after the compression test.The vertebral body augmented with CPS were also fractured severely and CPS were also crumbled into power.CPC were more severely power than CPS.The crack fracture was found in the vertebral body augmented with PMMA and the site of the crack fracture was at the interface between the vertebral body and PMMA.PMMA,however,remains intact without obvious cracks.The vertebral body augmented with CPB also has tiny cracks in the interface between the vertebral body and CPB,and tiny cracks also occurred in the surface of CPB.We found the interior of CPB remains intact and no crack after removing the surface of CPB.2.The decalcified group: The mean BMD decreased from 0.42 g/cm2 before decalcification to 0.23 g/cm2 after decalcification for 7 days,drop about 50% on average.Compared to the decalcified vertebral body,the biomechanical strength in CPB group can significantly higher than the control group and the CPC group(P<0.01).The biomechanical strength of the vertebral body augmented PMMA was similar to CPB(P>0.01).3.SD rats: The biomechanical strength of the control group and the sham group had no statistically significant difference(p>0.01).The biomechanical strength of the CPC group was significantly lower than the rest groups(p<0.01).The biomechanical strength of the CPB group was approximately 140 N.Compared to the sham group and the PMMA group,the biomechanical strength of the CPB group has no statistically significant difference(p>0.01).The fraction of the sham group and the control group is 5/6 after the three-point-bending test.All specimens fractured at the area of CPC in the CPC group and the fraction is 0/6.All specimens fractured at the area of PMMA and the fraction is 0/6.PMMA,however,has no breakage.All specimens,including four at the middle of the femur,one at the proximal femur and one at the area of CPB,fractured in the CPB group.The fraction of the CPB group is 4/6.【Conclusions】1.CPB can significantly enhance the biomechanical strength of fractured vertebral body and osteoporotic fractured vertebral body.2.CPB is good with the femur of rats.A close occlusal relationship has been formed in the adjacent interface between CPB and bone,which play a great role in supporting for the defect femur.CPB shows great medical application prospects.