| Improving the early osseointegration and long-term stability of titanium(Ti)-based implants is an important research point about orthopedic biomedical materials.Modified coating with controllable structure and strong bioactivity is of great significance to improving the clinical therapeutic effect of Ti-based implant.Strontium(Sr)is one of the essential trace elements of the human body.It has the dual effects of promoting bone formation and inhibiting bone resorption in the process of human bone remodelling.Therefore,preparing a bioactive Sr-containing phosphate coating on Ti by surface modification technology can effectively improve the bone-generating ability of Ti-based implants.Chemical conversion is a technology that uses metal-solution interface reactions to form a coating in situ.Because of its high coating-forming efficiency,high bonding strength,and no requirements on the shape of the substrate,this technology has attracted attention in the field of biomedical materials in recent yearsIn this study,using the in-situ growth mode of the chemical conversion method,a Sr-containing phosphate chemical conversion coating was prepared on the surface of medical Ti.The analysis and testing methods such as X-ray diffractometer,thermal field emission scanning electron microscope,mechanical testing machine and fourier transform infrared spectrometer were used to research characterization of coatings on Ti substrates.Effect of ratio of Sr2+ and Ca2+,pH value,Zn2+ concentration of conversion solution,and conversion time on the microstructure and properties of coatings on Ti was also systematicly researched.By adjusting the iron powder maturation process,the surface morphologies and microstructure of the conversion coatings were optimized.And the biological properties of the coatings before and after the maturation process by adding iron powder were also characterized to explore the cell behaviors on conversion coatings.The results show that the ratio of Sr2+ to Ca2+ concentration in the conversion solution can significantly affect the composition and microstructure of the conversion coatings.When the concentration of Sr2+ in the conversion solution is lower than that of Ca2+,a small amount of Sr-doped plate-like brushite crystals(Sr-CaHPO4·2H2O)formed on the surface of Ti substrate.On the contrary,when the Sr2+concentration is higher than that of Ca2+,a complete and uniform Ca-doped strontium hydrogen phosphate(Ca-SrHPO4)conversion coatings was prepared.Specifically,when the ratio of Sr2+ to Ca2+in the conversion solution is 11:7,the coating is the most uniform and dense,with the best bonding performance and corrosion resistance,and the bonding strength reaches 19.08 MPa.Zn2+ acted as a promoter as forming conversion coatings on Ti substrate.The addition of Zn(NO3)2·6H2O above 0.70 g/L is a necessary condition for the formation of complete Ti-based Ca-SrHPO4 conversion coatings.The change of pH value of the conversion solution and conversion time will not change the phase composition of the coatings,but will affect the integrity of the coatings.When the pH=3.50-3.75,and the conversion time exceeds 30 minutes,a uniform and dense conversion coating can be formed.The Ti-based Ca-SrHPO4 conversion coating prapared under apH value of 3.75 has the best corrosion resistance.The iron powder maturation treatment of the conversion solution will not change the phase composition of the conversion coating,but it can change the growth orientation of crystal plane during the crystallization of Ca-SrHPO4.Meanwhile,lamellar hierarchical structure appears on the surface of conversion coatings on Ti substrate.When the conversion time is 50 min,the surface of the Ti-based Ca-SrHPO4 conversion coating has both micro-scale and nano-scale flake crystals,which improves the hydrophilic wettability of the coating,and its contact angle is 64.12°.The in vitro cell culture experiments on coated-Ti samples showed that the Ca-SrHPO4 coatings prepared in the solution with and without maturation treatment both have good biocompatibility,which is beneficial to cell adhesion and proliferation. |
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