A Novel Approach to Designing a Rechargeable Fluoride Battery

Layered double hydroxides (LDHs), are a class of synthetic inorganic matrices that possess positively charged sheet-like structures that are counterbalanced through the intercalation of anions within their hydrated interlayers. Objectives: To determine whether LDHs have the desired properties to behave as novel materials capable of controlled release of fluoride. The adsorption and release characteristics of LDHs make them ideal candidates for the generation of a rechargeable fluoride-releasing vector, or ‘fluoride battery’ for incorporation into an array of dental materials for preventative applications. Methods: Zn-Al LDH was synthesised with structural characterisation achieved using powder-XRD and its capacity to absorb/release fluoride demonstrated over a range of sodium fluoride concentrations. The presence of fluoride uptake by LDH was confirmed using ¹⁹F^- NMR spectroscopy. To establish  this material’s application within dentistry, Zn-Al LDH was incorporated into a range of currently utilised polymeric resins. Results: The adsorption isotherm generated across a range of fluoride concentrations (0.5 - 100mM) revealed Zn-Al LDH to exhibit a maximal adsorption capacity of 44.7mg/g when placed in a 100mM solution of NaF for 1h. Release of the adsorbed fluoride was established upon placing NaF treated Zn-Al LDH into deionised water. Further experimentation utilizing LDH impregnated poly(ethyl methacrylate)/tetrahydrofurfutryl methacrylate (PEM/THFM) polymeric discs absorbed fluoride from a 100 mM solution of NaF for 24h, and demonstrated the capacity to release fluoride, raising the concentration of 5 ml deionised water to 1.4 mM (30 ppm) over a 5 day period. Conclusion: This rechargeable fluoride delivery system presents a viable candidate for the advancement of current systems delivering a beneficial therapeutic source of fluoride within the oral cavity, thus providing significant cariostatic effect. LDH technology can potentially be incorporated into a variety of dental materials, serving as a mechanism for prolonged release of fluoride, in addition to challenging the issue of poor patient compliance.