| ABSTRACT:Hydroxyapatite (HA, Ca,o(P04)60H2) coated titanium alloy has been widely used as implant materials in orthopedic and dental applications due to its outstanding bioactivity and biocompatibility. However, pure HA coating has a relatively high dissolution rate in the biological environment, which affects its long-term stability and makes the interface between bone and implant unstable. On the other hand, natural bone is a kind of calcium-deficient HA, which contains considerable amounts of additional elements including F, Mg, Sr and Zn, etc. Accordingly, modification of HA by incorporation of these elements is required to improve both bioactivity and long term stability of the apatite in terms of composition for clinical applications. Fluorine-doped hydroxyapatite Ca10(P04)6(OH)2-xFx (FHA, x is the degree of fluoridation) is reported to possess lower solubility and comparable bioactivity and biocompatibility over HA. Sr-substituted HA(SrHA) shows osteoinductive activity as well as higher solubility than HA. The current studies focus on the improvement in the bioactivity and solubility of coatings on Ti plant.The aim of this study is to fabricate biphasic coatings FHA/SrHA via sol-gel method. In such a constructed biphasic structure, FHA is considered the dissolution-resistant matrix, which can provide strong adhere to the Ti substrate, and SrHA the soluble phase. It is expected to obtain a novel bioactive ceramic coating with strong adherence and good stability for clinical applications through the synergetic effects of the coexistence of F and Sr elements.FHA/SrHA biphasic coatings (FHA/SrHA1, FHA/SrHA2and FHA/SrHA3with molar ratio of FHA to SrHA being1:1,1:2and1:3, respectively) were prepared on titanium substrate by sol-gel processes. Pure FHA and SrHA coatings are prepared as a control. The surface morphology of the coatings was analyzed by scanning electron microscope (SEM).The element composition and phase component were analyzed with energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The adhesion strength between the coating and substrate was evaluated using a scanning scratch tester. Dissolution behaviors were analyzed in TRIS and CPBS buffer solution.The ability to induce apatite precipitation on coating surfaces was evaluated in vitro by immersion in simulated body fluid (SBF). In vitro cell responses were evaluated using osteoblast-like MG63cells in terms of cell initial cell attachment (cell counting), morphology (inverted microscope and SEM), proliferation(MTT)and differentiation (alkaline phosphatase activity and osteocalcin level). We have the following results:1. FHA/SrHA biphasic coatings with different SrHA amount were successfully prepared on Ti substrate by sol-gel method. All FHA/SrHA biphasic coatings exhibit stronger adherence to Ti substrate than pure SrHA coating, but inferior adherence to pure FHA. The solubility of biphasic coatings and bonding strength between biphasic coatings and Ti substrate are adjustable and controllable by changing the addition amount of SrHA.2. The surface of Ti substrate after alkali pretreatment has the better porous structure, and is sodium titanate gel layer. Under the dual effects of mechanical and chemical bonds combination of occlusion, adhesive strength between Ti substrate and coatings are improved greatly. It can enhance the stability of biological coating Ti implanted materials, avoid large drop failure of coatings happen.3. All FHA/SrHA biphasic coatings exhibit a process of dissolving and re-precipitating calcium phosphate in TRIS and CPBS solution. The dissolution rate changes with the variation of phase constitution. However, biphasic coatings display good stability in comparison with pure phase coatings.4. All FHA/SrHA biphasic coatings exhibit the inducing ability for bone-like apatite formation upon soaking in SBF for14d. The XRD pattern indicates the diffraction peak intensity of apatite increased with increasing the SrHA amount. These findings imply that FHA/SrHA biphasic coatings are bioactive with biomineralization ability.5. All FHA/SrHA biphasic coatings has a positive effect on osteoblast proliferation and alkaline phosphatase activity and osteocalcin expression level, but the influence isn’t direct proportion with the content of SrHA in the coatings. FHA/SrHA2biphasic coating showed the highest influence in the osteoblast function response.6. The biological activity and biocompatibility of the biphase coatings is not with the increase of the content of SrHA in biphase coatings.lt prove that it exist a best proportion value of the amount of SrHA powder mixed in FHA gel.7. FHA/SrHA biphase coatings promote the activity of osteoblast.by synergy mechanism of fluorine, strontium, calcium, phosphorus ion released from coatings... |
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