Preparation And Bioactivity Of HA/ZnO Composite Gradient Coating Materials

Hydroxyapatite（HA）coating on the surface of Ti and its alloys can improve the bioactivity and biocompatibility of the coating materials.However,due to the mismatch of thermal expansion coefficient between HA and Ti based materials after sintering,the mechanical properties of the material are poor,which limits its application in the stressed parts such as bones,so it is necessary to improve the mechanical properties of HA Ti based coating materials.Therefore,it is an urgent problem to improve the mechanical properties of HA Ti-based coating materials.In this experiment,a gradient HA/ZnO composite coating material was prepared by zone electrophoresis followed by electrophoretic deposition（ZE/EPD）.The gradient distribution was formed by using two Ti substrates to zone electrophoresis firstly,and then the original cathode Ti substrate was used as anode for electrophoretic deposition after the new Ti substrate was inserted as cathode.The porous HA/ZnO composite gradient coating material was obtained after high temperature calcination.ZnO,SiO₂,SrCO₃ and MgO were used as modified compounds.HA/CS/ZnO/SiO₂,HA/CS/ZnO/SrCO₃and HA/CS/ZnO/MgO coating materials were prepared by ZE/EPD method.After calcination at 710℃,HA/ZnO/SiO₂,HA/ZnO/SrCO₃and HA/ZnO/MgO gradient coating materials were obtained.It was found that the internal elements of the coating presented gradient distribution in the radial direction of the coating by EDS preliminary test and analysis.The composition,crystal form,bonding strength,surface morphology and corrosion resistance of coating material were characterized by FT-IR,XRD,Universal Material Testing Machine,SEM and Electrochemical Workstation.The bacteriostatic property and in vitro bioactivity of the gradient coating were tested.The results show that the bonding strength of HA/ZnO/SiO₂,HA/ZnO/SrCO₃and HA/ZnO/MgO gradient coating materials with Ti substrate is 31.2 MPa,30.6 MPa and 31.4 MPa respectively,which is higher than that of the three coatings prepared by EPD.The three gradient coating materials have good corrosion resistance and bacteriostasis in the simulated body fluid of HEPES,and their self-corrosion current density and potential are 1.721×10^-8A.cm^-2,1.138×10^-8A.cm^-2,5.163×10^-8A.cm^-2and-0.314 V,-0.302 V and-0.049 V,respectively,and their bacteriostasis rates to Coliform bacteria are 81.7%,88.9%and 86.4%,and to Staphylococcus aureus are89.4%,89.7%and 89.9%,respectively.Through comprehensive analysis of the properties of composite coatings,HA/ZnO/SiO₂composite gradient coating materials have the best performance and are expected to be developed as a new generation of human bone implant replacement materials.