| Objective This study aimed to construct an ultrafast PL@Sr coating by co-mixing brown algae polyphenols and strontium chloride solution in three minutes.The coating can be deposited on the demineralized dentin surface to achieve dentin tubule sealing to reduce dentin sensitivity.Because fucoidan polyphenols promote dentin mineralization,this strategy also constructs a new dentin bionic remineralization system to achieve progressive and durable sealing of dentin tubules.Meanwhile,this study investigated the interaction between PL and Sr co-deposits and the effect of this new method of constructing a bionic remineralization system to induce remineralization of demineralized dentin,which provides a new idea to reduce tooth sensitivity and promote dentin remineralization.MethodsPart Ⅰ The main investigation was to investigate whether the co-deposition of PL and Sr occurred and to analyze the interaction between them.Dentin slices were treated with 37%phosphoric acid for 90 seconds and then rinsed with a sufficient amount of pure water to create a model of demineralized dentin.The dentin samples were randomly placed in four solutions for 3 min,the four solutions were:the Blank（Tris,pH=8.5）group,PL group,Sr group,and PL@Sr group.The dentin flakes of each group were observed for surface morphology using field emission scanning electron microscopy（Fe-SEM）,and the elemental composition of the PL@Sr coating surface was explored by X-ray photoelectron spectroscopy（XPS）;the PL@Sr co-mingled solution was dropped onto a copper grid and characterized by transmission electron microscopy（TEM）,and measured by attenuated total reflection Fourier transform infrared spectroscopy（ATR-FTIR）in the wavelength range of 4000-500 cm-1wavelength range of PL group,Sr group,and PL@Sr group powders to analyze the PL-Sr interactions.The reconstituted type I collagen membranes were used as a model,and the collagen membranes were treated with the above four solutions for 3 min followed by gradient dehydration and natural drying for the measurement of surface membrane potential and water contact angle.Part Ⅱ The ability and performance of PL@Sr induced remineralization of demineralized dentin.Firstly,the dentin slices treated with the above four different solutions were removed after4 and 24 hours,respectively,and the remineralization of dentin tubules and dentin collagen matrix was investigated by Fe-SEM,and the crystal orientation and composition of the remineralized material were characterized by X-ray diffractometry（XRD）and ATR-FTIR.The mechanical properties of PL@Sr dentin flakes and remineralized dentin were analyzed by friction wear and nanoindentation experiments using natural dentin as a control;the samples were treated with 5 wt%citric acids for seconds.The remineralized dentin was analyzed by characterizing the surface morphology of the treated samples and quantifying the residual calcium and phosphorus content in the solution by inductively coupled plasma emission spectrometry（ICP-OES）.The acid resistance of dentin.Part Ⅲ Biocompatibility and antibacterial ability of PL@Sr.Four groups of dentin slices treated with different solutions（Blank group,PL group,Sr group,PL@Sr group）were co-cultured with mouse fibroblast（L929）cells for 1,3,and 5days,respectively,and the in vitro cytotoxicity of PL@Sr was detected by CCK-8 assay of cell viability after co-culture and fluorescence staining to observe the morphological changes of cells after co-culture.4 groups of the above The dentin slices were sterilized by UV and ozone and placed in 24-well plates.40μL of Streptococcus mutans bacterial solution was added to the surface of the slices,and then 1 m L of culture medium was added after waiting for 4 hours.The slices were incubated in a 37℃thermostat.The optical density values of the bacteria（OD 660 nm）were detected by enzyme marker for 24 hours.Dilute each well of bacterial suspension to 1×105 times,take 60μL of the bacterial solution,and spread it evenly on the surface of the solid culture plate.Co-incubate for 24 hours at37℃and take pictures for counting the next day.Part Ⅳ In vivo experiments in the PL@Sr groupTwelve SD male rats（provided by the Medical Animal Experiment Center of Anhui Medical University）,about 4 weeks old and weighing about 150 g,were randomly divided into two groups:the blank group and the PL@Sr group,with six rats in each group.The in vivo dentin hypersensitivity model was successfully established by uniformly abrading about 1 mm of the bilateral maxillary first molar surfaces of the rats with a ball drill.The PL@Sr group applied the drug after brushing twice a day for 3 minutes each time.The blank group was brushed twice a day except for the rest as usual.The samples were left for1 day,and after 7 days of decortication and execution,the samples were removed,ultrasonically cleaned with saline for 60 seconds,and dried,and their surface morphology was observed by Fe-SEM.Results In this study,a copolymer coating of fucoidan polyphenols and strontium chloride was constructed on the demineralized dentin surface in a very short time（3 min）by a one-step co-deposition method.The surface morphology results showed that the coating formed an effective film-like structure that effectively achieved dentin tubule sealing and dentin surface modification.the PL@Sr coating was successfully immobilized on the collagen fiber surface by a simple one-step co-deposition strategy,and the modified collagen film had reduced negative potential and improved hydrophilicity.The results of the dentin remineralization experiments showed that the PL@Sr-modified dentin significantly promoted the remineralization of demineralized dentin after 4 h.After24 h,an enamel-like structure closely bound to the dentin could be observed on the dentin surface,and a large number of hydroxyapatite particles could be observed inside the dentin tubules.The results of the nanoindentation test,friction wear test,and acid resistance test showed that the mechanical properties of the remineralized dentin surface were higher than those of normal dentin,and its acid resistance was better than that of normal dentin.The results of in vitro cytotoxicity assay showed that PL@Sr co-deposits have good cytocompatibility.And a significant antibacterial ability could be seen by the turbidimetric method and counting.In vivo observation by Fe-SEM in mice showed the good dentin tubule sealing ability of the coating.Conculsion We developed a new strontium-rich coating that can fill the dentin tubules extremely fast and form a sheet-like sealing coating on the exposed dentin surface.The coating can promote the self-repair of dentin defects by enabling the co-deposition of fucoid polyphenols（PL）and strontium chloride（denoted as PL@Sr）in a simple and rapid one-step method,which can provide an economical,rapid,and effective treatment strategy for dentin-sensitive diseases caused by dentin exposure and root surface caries. |
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