Study On Effect Of Strontium Content On Properties Of Strontium And Silver Doped Micro-arc Oxidation Coatings

Objectives In this study,Sr-Ag doped micro-arc oxidation coatings with different strontium?Sr?contents were prepared on pure titanium and the physical/chemical properties of the coatings as well as adhesion,proliferation and osteogenic differentiation of preosteoblasts on the coatings before and after sample immersion were examined to explore the short-term and long-term osteogenic property of Sr in Sr-Ag doped micro-arc oxidation coatings,its acting mechanism and optimal Sr content,to provide experimental basis on developing new kind of dental implants with good osteogenic coatings.Methods 1 Preparation of Sr-Ag doped micro-arc oxidation coatings with different Sr contents and analysis of their physical and chemical properties.The samples were divided into five groups,Sr0 group,Sr30 group,Sr60 group,Sr90 group and Sr120 group.Coatings with different strontium contents were prepared by micro-arc oxidation technique in electrolyte containing 0.17g/L silver nitrate and 0g/L,30g/L,60g/L 90g/L and 120g/L strontium acetate,respectively.Scanning electron microscopy?SEM?observation,energy spectrum analyzer?EDS?and X-ray diffractometer?XRD?analysis,roughness measuring,contact angle analysis and inductively coupled plasma optical emission spectrometer?ICP?were used to detect micromorphology,chemical compositions,roughness,hydrophilicity and Sr²⁺release of/from the coatings,respectively,before and after soaking in PBS.2 The effect of Sr within different coatings on adhesion,proliferation and osteogenic differentiation of preosteoblasts.The coatings from group Sr0,Sr30,Sr60,Sr90 and Sr120were soaked in phosphate buffered saline?PBS?at 37°C for 30 days and the PBS were changed everyday.MC3T3-E1 cells,a pre-osteoblast cell line,were seeded on the coatings with or without PBS soaking.Cell adhesion on the coatings was examined by nucleus propidium iodide?PI?staining 2 hours after cell seeding,and cell proliferation analysis was performed with a cell proliferation-toxicity test kit?CCK-8?at day 1,3,5 and 7.SEM and fluorescent microscope were used to observe cell growth on the coatings 24h after cell seeding.Alkaline phosphatase?ALP?activity,a marker for osteoblastic differentiation,was also evaluated to elucidate the osteogenic property and determine the optimal content of Sr within the Sr-Ag doped micro-arc oxidation coatings.Results 1 Preparation of Sr-Ag doped micro-arc oxidation coatings with different Sr contents and analysis of their physical and chemical properties.Sr-Ag doped micro-arc oxidation coatings with different Sr contents were prepared and divided into five groups,group Sr0,Sr30,Sr60,Sr90 and Sr120,based on different concentration of strontium acetate in electrolyte.SEM observation showed that micromorphology of coating surfaces were similar in all five groups and crater-like micropores,with a diameter of 0.5²?m,formed on all coating surfaces.No significant difference was observed for micropore diameter among five groups?p>0.05?.EDS analysis demonstrated that Sr contents in group Sr30,Sr60,Sr90 and Sr120 were 9.64%,15.08%,18.23%and 21.25%,respectively.Sr element was not found in the Sr0 group.Sr content within the coatings increased with the increase of strontium acetate concentration in electrolyte.XRD showed that the diffraction peak of SrTiO₃ were observed in four Sr-doped coatings and magnitude of SrTiO₃diffraction peak increased with the increase of Sr content in coatings.Roughness and contact angle tests showed that there was no significant difference in surface roughness and hydrophilicity among five groups?P>0.05?.Above results indicated that Sr content within the coatings had no significant influence on micromorphology,roughness and hydrophilicity of Sr-Ag doped micro-arc oxidation coatings.Sr²⁺release test showed that a fast Sr²⁺release was observed within first 7 days and the release slowed down quickly thereafter.The cumulative Sr²⁺release within first 7 days in group Sr30,Sr60,Sr90 and Sr120 were 0.446,4.593,10.326 and 15.994 ppm,respectively,and cumulative Sr²⁺release kept at a relatively stable level later.Whereas average Sr²⁺release each day decreased sharply within first 7 days and it kept at a very low level thereafter.Average daily Sr²⁺release in group Sr30,Sr60,Sr90 and Sr120 were 0.013,0.017,0.098 and0.067ppm respectively from day 4 to day 7,0.002,0.012,0.016 and 0.03 ppm respectively from day 8 to 30,and 0.0004,0.0005,0.002 and 0.003ppm respectively from day 31 to day120.Average Sr²⁺release each day after day 4 was far below the Sr²⁺concentration?0.87ppm?reported in literature,which could promote preosteoblast osteogenic differentiation.EDS examination showed that Sr contents within coatings in group Sr30,Sr60,Sr90 and Sr120 after soaking in PBS for 30 days were 8.58%,12.89%,14.52%and16.59%,respectively.Compared with those before PBS coating,Sr contents had a respective decrease of 11.00%,14.52%,20.35%and 21.93%.XRD showed that only small SrTiO₃ diffraction peak existed in group Sr120 and it was not observed in other three groups.2 The effect of Sr within different coatings on adhesion,proliferation and osteogenic differentiation of preosteoblasts.There was no significant difference for adehesion cell numbers of pre-osteoblasts among group Sr0,Sr30,Sr60,Sr90 and Sr120before PBS soaking?P>0.05?and after PBS soaking for 30 days?P>0.05?.Examination of MC3T3-E1 cell proliferation showed that before PBS soaking,cell proliferation in group Sr60,Sr90 and Sr120 were higher than that in Sr0 at day 1,3,5 and 7?P<0.05?and higher than that in group Sr30 at day 3 and 5?P<0.05?.After PBS soaking,although highest cell proliferation was observed in group Sr120 at all four time points,no significant difference was found among five groups,except at day 7,cell proliferation in group Sr120 was significantly higher than that in group Sr0 and Sr30?P<0.05?.ALP activity test showed that before PBS soaking,ALP activity in four Sr-doped groups were all significantly higher than that in group Sr0?P<0.05?and ALP activity in group Sr 90 and Sr120 were also significantly higher than those in group Sr30 and Sr 60?P<0.05?.After PBS soaking,group Sr90 and Sr120 still showed increased ALP activity which were significantly higher than those in other three groups?P<0.05?.Above results indicated that Sr in Sr-Ag doped micro-arc oxidation coatings could promote preosteoblast proliferation and osteogenic differentiation and its effect increased with the increase of Sr content within coatings,but Sr showed no significant effect on early adhesion of preosteoblasts.After soaking in PBS for 30 days,the coatings in group Sr90 and Sr120?with a 18.23%and 21.25%Sr content?still kept a long-term effect on promoting preosteoblast proliferation and osteogenic differentiation.As Sr²⁺release test during PBS soaking showed that average Sr²⁺release each day after day 4 was far below the Sr²⁺concentration?0.87ppm?promoting osteoblast differentiation,the osteogenic effect in group Sr90 and Sr120?with a 18.23%and 21.25%Sr content?may not be attributed to Sr²⁺released from coatings,but to Sr integrated on coating surface.Conclusions 1 Sr-Ag doped micro-arc oxidation coatings with different Sr contents were prepared and Sr content did not affect the micromorphology,roughness and hydrophlicity of the coatings.2 Sr in Sr-Ag doped micro-arc oxidation coatings could promote adhesion,proliferation and osteogenic differentiation of preosteoblasts and Sr with a content from18.23%to 21.25s%?mass%?not only had excellent short-term effects on osteogenic differentiation of preosteoblasts but also exhibited good long-term effects.3 Not only Sr⁺released from Sr-Ag doped micro-arc oxidation coatings could promote proliferation and osteogenic differentiation of preosteoblasts,but also Sr integrated on coating surface play a role in preosteoblast proliferation and differentiation.Figure:21;Table 3;References 83...