A Novel Sustained Release Fluoride Strip Based Poly（propylene Carbonate） For Preventing Caries

Background: With the depletion of petroleum resources and the aggravation of environmental problems caused by white pollution,the development and popularization of biodegradable polymer materials has become an inevitable trend.Polymer-based drug delivery system has been widely used in the field of oral cavity,which can improve drug utilization,reduce drug side effects and administration frequency.Poly（propylene carbonate）（PPC）is an aliphatic polyester made by propylene oxide and carbon dioxide copolymerization,which due to its excellent biodegradability and biocompatibility.It is widely used in tissue engineering,medical supplies,drug delivery systems and medical implant materials.Fluoride has always been regarded as the most effective anti-caries drug,which mainly acts by promoting remineralization,inhibiting demineralization,interfering with bacterial metabolism and plaque formation.The development of targeted and low-concentration sustained-release preparations is the direction of fluorine-containing preparations.The aim of this study is to synthesize a novel fluoride strip based poly（propylene carbonate）（PPC）,which can improve oral fluoride retention for desirable anticaries effect with minimal side effects.Methods: 1.This study developed fluoride-loaded poly（propylene carbonate）（PPC,Mn=20K）strips with different fluoride contents（0%,1.25%,2.5% and 5% Na F-PPC）.2.The Na F-PPC strips were synthesized by melt-blending method and characterized by scanning electron microscopy（SEM）,X-ray diffraction（XRD）,differential scanning calorimetry（DSC）and universal testing machine.3.Fluoride ion selective electrode method was used to explore the release of fluoride and the cumulative release rate of fluoride.The drug loading and encapsulation efficiency were also calculated.The mechanism of drug release was investigated by using zero-order equation,first-order equation,Higuchi equation and Korsemeyer-Peppas equation models.4.Artificial early enamel caries used as a model,the surface morphology characteristics of enamel blocks were observed by scanning electron microscopy（SEM）,and the enamel surface microhardness（SMH）were measured by Knoop Hardness Tester,which to evaluate the remineralization properties of PPC/Na F strips with different fluoride contents.Results: 1.The results of SEM and XRD indicated fluoride was successfully entrapped in PPC/Na F strips and spread uniformly within the polymer matrix.Compared to the control films,mechanical performances of PPC/Na F strips presented no significant effect on tensile strength values and elongation at break.2.In vitro release experiments showed that PPC/Na F strips with three different drug concentrations could be continuously released in sustained manner with no burst effect during 24 days,and their cumulative release rates were 90.67%,93.21% and 94.52%,respectively.The drug loading rate of the patch increased by 0.72%,1.21% and 2.65% with the increase of drug content,and its encapsulation rate was 57.76%,52.92%and 55.71%,respectively.The release profile followed the first-order kinetics,and the diffusion exponent（n）values obtained from the Korsemeyer-Peppas model were n<0.5,which indicated Fickian diffusion mechanism.3.Compared with the control group,the microhardness values of other groups were significantly increased（P<0.05）;The surface microhardness of enamel specimens in 1.25% PPC/Na F group,2.5%PPC/Na F group and 5% PPC/Na F group was increased,and the difference between groups were significant（P<0.05）.The SEM results showed that the number of pores on the enamel surface of PPC group was still large,and irregular granular sediments were observed.In 1.25% PPC/Na F group,the number of pores on the enamel surface decreased significantly.However,obvious enamel collapse was still observed on the surface and mineral crystal deposition was loose and uneven;in 2.5% PPC/Na F group,there were almost no pores on the enamel surface.The enamel surface was regular and covered with a large number of needle-like crystals,which were densely arranged;in 5% PPC/Na F group,the enamel surface was covered with a large number of needle-like or irregular granular crystals and layered sediments were observed in some areas.Conclusion: PPC/Na F strips have good sustained release performance.With the increase of fluoride content in PPC/Na F strips,its remineralization ability also increases,which is expected to be applied in the prevention and treatment of early enamel caries.