Low Temperature Sythesized ?-Tricalcium Phosphate Bone Cement And Its Mechanical Properties Enforced By RGO/CNTs

Calcium phosphate cement(CPC)has been widely applied in non-load-bearing bone defect treatment because of its advantages in rapid setting,excellent bioactivity and biocompatibility,non-cytotoxicity,etc.However,low strength and high brittleness are inherent disadvantages of CPC,which restricted its applications in load-bearing bone defect repairing.Moreover,setting time is also an important index to evaluate CPC.Unset CPC powders would be dispersed by body fluid and causing inflammation if the setting time is too long.?-tricalcium phosphate(a-TCP)is one of the most commonly CPC.However,complex preparation technology and high cost limit the application of ?-TCP.Therefore,?-TCP with simplified preparation technology,low cost,higher mechanical properties and proper setting time could have broader applications.In this article,a-TCP was used to prepare CPC.Firstly,the preparation technology of ?-TCP was optimized to obtain ?-TCP with better performance.And then,two kinds of methods was used to improve the mechanical properties of CPC.One is to adjust the ratio of calcium and phosphorus of CPC by using tetracalcium phosphate(TTCP).Another is reduced graphene oxide(RGO)and carbon nanotubes(CNTs)as reinforcement.Further research on the influence of microwave to the mechanical properties and setting time of RGO/CNTs-CPC composite was carried since RGO and CNTs can absorb microwave.Finally,the biological activity of RGO/CNTs-CPC composite were studied.Main research contents and results are listed as follows:(1)Amorphous tricalcium phosphate(ACP)with special structure was prepared by chemical precipitation using P-cyclodextrin as template.Pure ?-TCP was obtained by sintering ACP at 650 ? for 3 h.The influences of different ACP,sintering temperature and sintering time on a-TCP product were studied.Comparing with traditional methods,this method greatly reduced the sintering temperature and optimized the preparation technology.The setting time and the mechanical properties were better than a-TCP prepared by traditional methods.(2)The calcium-phosphorus ratio of a-TCP is lower than that of hydroxyapatite HA.Therefore,the setting product was calcium deficient hydroxyapatite(CDHA).TTCP is the only calcium phosphate with calcium-phosphate ratio higher than HA.In this article,calcium-phosphate ratio of a-TCP bone cement was adjusted by TTCP,to make the calcium-phosphate ratio of CPC close to HA.This will improve the crystallization of setting product and obtain better mechanical properties.Research shows that,the mechanical properties of CPC will reach the highest level when the mole fraction of TTCP was 30%.Comparing with CPC specimens without TTCP,the flexural strength and compressive strength improved by 21.88%and 13.45%respectively.Nevertheless,the deficiency of this method is the setting time of CPC composites was greatly extended by the addition of TTCP.(3)So far,graphene has the most excellent mechanical properties,and also the CNTs.In this article,RGO and CNTs were added in ?-TCP bone cement as reinforcement,they can released the energy of crack propagation by crack deflection,branching,interface dissociation,bridging,pulling out,suffering stress and load transfer,thus improve the mechanical properties of CPC.The results showed that when using RGO alone,the mechanical properties reached a maximum with the content of RGO was 0.2 wt%.Comparing with CPC specimens without RGO,the flexural strength and compressive strength increased 33.56%and 20.93%respectively.CNTs used along with RGO as reinforcement,the flexural strength and compressive strength would increase 67.13%and 76.38%respectively when the content of RGO was 0.2 wt%and CNTs was 0.6 wt%.RGO/CNTs-CPC composite exhibited shorter setting time because RGO and CNTs can absorb some water to reduce the liquid in bone cement.(4)RGO and CNTs can absorb microwaves,which leads to the temperature rise.Water also can absorb microwaves to make water molecules move faster.During the setting of RGO/CNTs-CPC composites,microwave can speed up the setting reaction and shorten the setting time.Meanwhile,microwave treatment can eliminate the bubbles from the interface between RGO,CNTs and substrate materials.This will increase the interface bonding strength,consequently,the mechanical properties of RGO/CNTs-CPC composites will be improved.The results showed that the final time was shortened nearly a half,and flexural strength and compressive strength increased 19.86%and 21.68%respectively after microwave treatment.(5)Simulated body fluid(SBF)soaking method can evaluate the biological activity of materials by the forming ability of bone-like apatite.When RGO/CNTs-CPC composites were soaking in SBF,a layer of bone-like apatite formed on the surface of composites.The quantity of bone-like apatite increased with the prolongation of immersion time.which demonstrated an excellent biological activity of RGO/CNTs-CPC composites has.