Preparation And Properties Of Bioactive Calcium Citrate Composite Bone Cement

In various trauma and chronic diseases such as osteoporosis,the incidence of fractures and bone defects has significantly increased.How to make fractures and bone defects better and faster healing has become one of the hot issues of orthopedic surgeons.Because of the current clinical application of artificial bone filler repair materials such as hydroxyapatite,calcium phosphate,calcium sulfate exist some defect,for example the brittle nature,lacking of mechanical properties and the too slow or fast degradation rate and other factors,leading to their limited use in clinical application.Therefore,it is necessary to further develop new bone filling repair materials.In this paper,the bone cement with calcium citrate as the main raw material was studied,the setting time,compressive strength,anti-washout capacity,in vitro degradation,curing characteristics and in vitro cellular properties of the bone cement were studied,and the calcium citrate composite bone cement was further used to characterize bone repair in animals.Chitosan/calcium citrate（CS/CC）powder was synthesized by coprecipitation method,and we chose citric acid/sodium citrate liquid as the setting liquid to prepared a new type of bone cement which can fast cure in air.The physicochemical performance results indicate that,when the weight ratio of CS/CC is 1/5 and liquid/powder is 0.4m L/g,the setting time and compressive strength of the cement are both appropriate value,the final setting time is 17 min and the compressive strength of the bone cement reaches 53 MPa after curing in air for 14 d.The anti-washout capacity and degradation rate of CS/CC bone cement was significantly improved compared to the CC bone cement after immersed in PBS（pH=7.2）,the degradation rate of CS/CC bone cement reaches 5.1% after soaked for 120 h,the citric acid solution used to dissolve chitosan in the preparation of CS/CC composite powder reduced the PH value of the cement soaked in PBS,the pH tends to stabilized after soaking 24 h and reached 4.6 for 120 h immersed,which was a certain differences with the pH environment of the human body.The addition of CS makes CS/CC composite bone cement with higher reactivity,which leading to the generation of CaCO₃·6H₂O in air setting and Ca₈H₂（PO₄）₆·5H₂O in 5×SBF immersing.However,there is virtually no curing product of CC bone cement setting in air and a small amount of Ca₉（HPO₄）（PO₄）₅（OH）was deposited when soaked in 5×SBF.The L929 cells were cultured by the medium extract of CC bone cement and CS/CC bone cement to evaluate the cytotoxicity of bone cement,the results show that CS/CC bone cement is more toxic than pure CC bone cement,the two acidic extracts both have obvious inhibitory effects on the growth and proliferation of basophilic L929 cells,and this inhibition has concealed the Ca²⁺ of calcium citrate and the cell bioactivity of chitosan,which can provide a beneficial environment for cells.Considering that CC powder was not high in similarity to natural bone constituents and its own weakly acidic,in the study,calcium phosphate powder [Hydroxyapatite（HA）or tetracalcium phosphate/calcium hydrogen phosphate（TTCP/DCPA）] of weakly alkaline and good biocompatibility was selected to compound with the CC powder,then we chose 0.5mol/L K₂HPO₄/KH₂PO₄ which has coagulation effect as the setting liquid and prepared the calcium phosphate/calcium citrate composite bone cement,the cement can be cured quickly under conditions in the air.The physicochemical performance results indicate that,the calcium phosphate/CC bone cement with flake CC have the excellent setting time and compressive strength,especially when the liquid/powder is 1m L/g and the weight ratio of HA/CC is 1/3,the compressive strength of HA/CC bone cement reaches 39 MPa after 14 d curing,and when the liquid/powder is 0.8mL/g and the weight ratio of（TTCP/DCPA）/CC is 1/2,the compressive strength of the bone cement is about 35 MPa.Moreover,the final setting time of the two bone cement is within 25 min,and their compressive strength is greater than that of pure CC bone cement when liquid-solid ration is 0.8mL/g,which indicate that the mechanical properties of the composite bone cement are improved by adding calcium phosphate.After soaked in PBS（pH=7.2）,（TTCP/DCPA）/CC bone cement has the best anti-washout capacity,and the in vitro degradation rate of（TTCP/DCPA）/CC bone cement is obviously controlled,it is 10.1% after soaking in PBS for 28 d.After immersed in PBS,（TTCP/DCPA）/CC bone cement was almost not change the pH of the liquid,the pH stabilized at 7.21 for 28 d soaking,which is very similar with the pH environment of human body.The XRD and FTIR results show that,（TTCP/DCPA）/CC bone cement can produce a precursor of hydroxyapatite Ca₄H₂(P₃O₁₀)₂ after setting in the air,and the deposition of calcium phosphate such as HA,Ca₃（PO₄）₂ and Ca₄H₂(P₃O₁₀)₂ at the bone cement surface were induced by soaking in SBF,indicating that the（TTCP/DCPA）/CC bone cement has a good bone-inducing activity in vitro.In order to evaluate the cytotoxicity of bone cement,the L929 and MSC cells were cultured by the medium extract of CC bone cement and（TTCP/DCPA）/CC bone cement,the results show that the extract solution of（TTCP/DCPA）/CC is non-toxic to the two cells.In order to evaluate the cell adhesion,bone cement was coincubated with MG63 cells,the results show that,the growth,proliferation,adhesion and crawling ability of the MG63 cells on（TTCP/DCPA）/CC composite bone cement was better.Fill the CC bone cement and（TTCP/DCPA）/CC bone cement in the bone defect of the animal,the operation results show that,neither group of animals had any surgical complications,and the two groups of bone cement showed good degradation activity and bone induction in vivo,and more new bone was generated of（TTCP/DCPA）/CC group than CC bone cement filling group.