| Objectives The aim of this study was to develop a one-step PDA-assisted co-deposition strategy to immobilize PDA and PAA onto dentin collagen fibers to inducing dentin remineralization.We hypothesize that the PDA@PAA coatings can mimic the effect of NCPs to promote dentin remineralization,including occluding dentin tubules,remineralizing demineralized-dentin collagen matrix,and regenerating a layer of enamel-like precipitates to repair defective tooth.Methods The first part mainly explored the interaction and co-deposition between PDA and PAA.Dopamine（DA）undergoes oxidation and self-polymerization under alkaline aerobic conditions to form a complex polydopamine（PDA）structure that adheres to the surface of the material to achieve the modification of the surface of the material.The experiment was divided into four groups:PDA@PAA group（DA and PAA mixed solution）,PDA group（DA solution）,PAA group（PAA solution）,control group（distilled water）.X-ray photoelectron spectroscopy（XPS）was used to characterize the silicon wafers pretreated with the above four groups of solutions to explore whether PDA and PAA co-deposited on the surface of silicon wafers.The attenuated total reflection Fourier transform infrared spectroscopy（ATR-FTIR）technique was used to measure the infrared spectra of the freeze-dried samples in the wavelength range of 4000-500cm-1 after 24hours of reaction with four solutions to detect the interaction between PDA and PAA.The four groups of solutions after 24 hours of reaction were dropped onto nickel net and naturally dried for the transmission electron microscopy（TEM）characterization to explore the influence of the addition of PAA on the polymerization reaction of PDA.The UV–vis absorption spectra of the resulting solutions（diluted in the same proportion）were obtained with a UV-visible spectrophotometer to measure the ultraviolet-visible spectra of the four groups of solutions in the range of 200-700nm before the reaction and 24 hours after the reaction to explore the influence of the addition of PAA on the oxidative polymerization of DA.In the second part,the recombinant type I collagen membrane was used as a model to explore the interaction between PDA@PAA and type I collagen,and the changes in the physical and chemical properties of collagen modified by PDA@PAA.The collagen membrane was subjected to a series of tests after being treated with the above four solutions for 24 hours.ATR-FTIR was used to measure the infrared spectra of four groups of collagen membrane in the wavelength range of 4000-500cm-1 to evaluate the molecular interaction between PDA@PAA and collagen.The collagen membrane was placed on the water contact angle detection platform for static contact angle measurement,with deionized water as the test solution,5 samples for per group（n=5）,and the difference of hydrophilic and hydrophobic properties of four groups of collagen membrane was evaluated.The zeta potential on the surface of the four groups of collagen membranes was measured to evaluate the changes in the surface potential.The surface morphology of the modified collagen was characterized by field emission scanning electron microscope（FE-SEM）to observe the changes of the surface morphology after modification.The third part explored the cytotoxicity of PDA@PAA co-deposition and its ability to induce remineralization of demineralized dentin.Forty-eight of intact third molars were collected and prepared with a size of 4 mm×4 mm×1.5 mm,and the dentin slices were treated with 37%phosphoric acid for 60 seconds to establish a demineralized dentin model.The samples were randomly divided into four groups.And the samples were treated with the above four groups of solutions for 24 hours,which were denoted as:PDA@PAA group,PDA group,PAA group,and control group.First,the above four groups of dentin samples were co-cultured with Sprague-dawley（SD）rat bone marrow mesenchymal stem cells（SD-BMSCs）for 1 day,4 days,and 7 days.Cell viability after co-culture with four groups detected by CCK-8 and morphological changes after co-culture observed by fluorescence staining were used to detect the cytotoxicity of PDA@PAA co-deposition in vitro.Then,the ability of PDA@PAA to induce demineralized dentin remineralization was investigated.In this study,supersaturated calcium-phosphorus solution without NCPs was used as the mineralized medium.Four groups of dentin samples were immersed in the mineralized solution for 8 hours 12 hours and 24 hours respectively to conduct a series of characterization.The remineralization of dentin was characterized by SEM,energy dispersive spectrometer（EDS）and TEM.The crystal orientation and composition of remineralization were characterized by selected area electron diffraction（SAED）and X-ray diffraction（XRD）.The mechanical properties of remineralized dentin were analyzed by friction and wear experiments and nano indentation experiments,and the natural enamel,dentin and demineralized dentin used as the control.The samples were treated with 6 wt%citric acid for 1 minute,and the acid resistance of the remineralized dentin was analyzed by characterizing the surface morphology of the samples before and after treatment and quantitatively detecting the residual calcium and phosphorus content in the treated solution by inductively coupled plasma optical emission spectrometer（ICP-OES）.Results After mixing DA with PAA,in the process of oxidative polymerization of dopamine to form PDA,PDA assisted PAA co-deposited and formed a composite coating PDA@PAA on the surface of the demineralized dentin via the hydrogen bonding between them.And PAA significantly suppressed the aggregation process and inhibited the aggregation of PDA,resulting nanosized PDA particles.PDA@PAA was successfully fixed on the surface of collagen fibers through a simple one-step co-deposition strategy,forming nano-PDA particles into the collagen network.It showed that the negative surface zeta potential and hydrophilicity increased after PDA@PAA co-deposition modification.The results of in vitro cytotoxicity showed that PDA@PAA co-deposition had good cytocompatibility.The PDA@PAA co-deposited coating had good cytocompatibility,successfully and effectively promoted the demineralized dentin remineralization.The demineralized-dentin modified with PDA@PAA was completely remineralized at 12 h,not only the dentin tubules were occluded,but more importantly,the demineralized dentin collagen matrix was remineralized.Moreover,after mineralization for 24 h,a dense mineral layer similar to enamel structure was regenerated on the surface of dentin and closely combined with dentin.The results of mechanical properties and acid resistance suggested that the mechanical properties of the regenerated enamel-like structure are close to that of enamel,and its acid resistance is better than that of enamel.Conclusion A novel,easy,and promising management of dentin expose and dentin surface demineralization was developed by PDA-assisted PAA co-deposition（PDA@PAA）onto the surface of dentin collagen to promote dentin remineralization.PDA@PAA co-deposition can induce HA growth to occlude the dentinal tubules,remineralize the demineralized-dentin collagen matrix,and regenerate a layer of enamel-like tissue to cover the dentin surface with its mechanical properties similar to those of enamel.This PDA-assisted PAA co-deposition strategy provided a potential to self-heal the dentin defect similar to the hard tooth structure.In addition,this mineralization strategy,as a general mineralization strategy,can induce the mineralization of multiple substances. |
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