| Background and Objective:Due to the increasing demand for aesthetic and non-metallic implants,zirconia has become a popular alternative to titanium implants because of its similar color to teeth and good biocompatibility and chemical stability.Similar to titanium and its alloys,zirconia is also a biological inert material,which does not have the properties of osteoconduction and osteoinduction after implantation,and cannot form a direct bone combination with the surrounding bone tissue.In order to evaluate osteogenesis ability of zirconia materials,a composite coating containing trace silicon,strontium and fluorine multi-doped hydroxyapatite(mHA)and bone morphogenetic protein 2(BMP-2)was formed on the surface of zirconia by polydopamine(PDA)-assisted impregnation method,and a nanozirconia coating was prepared on the surface of zirconia substrates in advance in consideration of improving the bonding strength between the composite coating and zirconia substrate.The purpose of this study is to explore the feasibility of preparing PDA/mHA/BMP-2 composite coating on the surface of zirconia by polydopamine-assisted impregnation method,which is firmly bonded to the substrate and has good osteoconduction and osteoinduction properties.Methods:This study is mainly divided into two parts:Part one: preparation and characterization of PDA/mHA/BMP-2 composite coating.Firstly,a uniform nano-zirconia coating was formed on the surface of zirconia substrate,and then PDA/mHA/BMP-2 composite coating was prepared by polydopamine-assisted impregnation method,and the morphology of the coating was observed by field emission scanning electron microscope(FE-SEM).The wettability of each coating surface was detected by automatic optical dynamic and static contact angle meter;the phase change of zirconia was detected by X-ray diffraction(XRD);the chemical composition of composite coating was studied by Fourier transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS).Ultrasonic cleaner and FE-SEM were used to qualitatively detect the bonding strength between each coating and zirconia substrate.Part two: study on the biological properties of PDA/mHA/BMP-2 composite coating in vitro.The osteogenic properties of PDA/mHA/BMP-2 composite coating were studied by coculturing the samples of each group with mouse osteoblast precursor cells MC3T3-E1 in vitro,including(1)cytotoxicity experiment,(2)cell adhesion and extension experiment,(3)cell proliferation experiment,(4)cell osteogenic differentiation related experiments: ALP activity,osteoblast related gene Runx2,ALP,OCN expression and alizarin red staining.Results:Part one: preparation and characterization of PDA/mHA/BMP-2 composite coating.The results of FE-SEM observation show that the nano-zirconia coating spreads uniformly,and the particle diameter is about 30 nm.The rod-like mHA particles wrapped by PDA and spherical BMP-2 protein molecules can be seen on the surface of the composite coating.The results of contact angle meter showed that the hydrostatic contact angle of zirconia surface treated by PDA/mHA/BMP-2 composite coating was 52.83 °±3.55 °,which was 41% lower than that of untreated zirconia substrate(89.25 °±1.42 °).The FTIR spectrum was consistent with the FTIR functional group information of PDA reported in the literature;XPS detected the existence of C,N,O,Ca,P,Zr elements,which was consistent with the composition of PDA/mHA/BMP-2 composite coating.After ultrasonic cleaning for 1 hour,the PDA/mHA coating prepared on the untreated zirconia surface fell off completely,while a large number of PDA/mHA agglomerates remained on the zirconia surface pretreated with nano-zirconia.Part two: study on the biological properties of PDA/mHA/BMP-2 composite coating in vitro.The results of cytotoxicity showed that the MC3T3-E1 cultured with the 100%,50%,10% extract of PDA/mHA/BMP-2 coated zirconia grew well,and the number of cells adhering to the surface of PDA/mHA/BMP-2 coated zirconia for 5 hours and 24 hours were1.39 and 1.99 times higher than those of untreated zirconia,respectively.After co-cultured with MC3T3-E1 cells for 10 days,compared with the untreated zirconia group,the cell proliferation rate in the PDA/mHA/BMP-2 coated zirconia group increased by 48% and the ALP activity increased by 78%.After co-culture with MC3T3-E1 cells for 14 days,the number of calcium nodules in the PDA/mHA/BMP-2 coated zirconia was significantly more than that in the untreated zirconia group,and the expression of osteogenesis-related genes Runx2,ALP and OCN in the PDA/mHA/BMP-2 coated zirconia group was 12.37,7.88 and12.07 times higher than that in the untreated zirconia group,respectively.Conclusions:Part one: preparation and characterization of PDA/mHA/BMP-2 composite coating on zirconia surface.(1)PDA/mHA/BMP-2 composite coating can be prepared on zirconia surface by polydopamine-assisted impregnation method,which improved the hydrophilicity of zirconia.(2)The zirconia substrate was pretreated by polydopamine-assisted chemical deposition for the first time,and a uniform nano-zirconia coating was formed on the surface,which is beneficial to improve the bonding strength between the zirconia substrate and the composite coating.Part two: study on the biological properties of PDA/mHA/BMP-2 composite coating in vitro.(1)The PDA/mHA/BMP-2 composite coating on the surface of zirconia prepared by polydopamine-assisted impregnation method is safe,non-toxic and has good cytocompatibility.(2)The PDA/mHA/BMP-2 composite coating with both osteoconduction and osteoinduction properties was prepared on the surface of zirconia by polydopamine-assisted impregnation method for the first time,which improved the osteogenesis ability of zirconia materials and provided a new strategy for the surface modification of zirconia implants. |
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