Structure, biomineralization and biodegradation of Ca-Mg oxyfluorosilicates synthesized by inorganic salt coprecipitation
Abstract
In this research, a novel group of Ca-Mg oxyfluorosilicates containing different levels of fluoride substituting for oxide was synthesized by an inorganic salt coprecipitation process followed by calcination/sintering. The effects of the incorporation of fluoride on the resultant structural characteristics, apatite-forming ability and biodegradability were evaluated by X-ray diffraction, transmission electron microscopy, scanning electron microscopy/energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, inductively coupled plasma spectroscopy and pH measurements. According to the results, the samples containing up to 2 mol% F present a single-phase structure of diopside (MgCaSi2O6) doped with F. It was also found that to meet the most biomineralization characteristic, the optimal value of fluoride in the homogeneous samples is 1 mol%. In this regard, on the one hand, the partial incorporation of fluoride into apatite (via forming fluorohydroxyapatite) and, on the other hand, the absence of fluorite (CaF2) as a consumer of Ca in the deposits are responsible for achieving the most apatite-forming ability circumstance controlled by an ion-exchange reaction mechanism. In conclusion, this study reflects the merit of the optimization of fluoride-doping into Ca-Mg silicates for development in biomedicine.
Summary
This paper investigates the synthesis and characterization of novel Ca-Mg oxyfluorosilicates with varying fluoride content, fabricated via an inorganic salt coprecipitation method followed by calcination/sintering. The main research question is to determine the optimal fluoride doping level within diopside (MgCaSi2O6) to maximize its biomineralization and biodegradability for biomedical applications. The authors employed a range of techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma spectroscopy (ICP), and pH measurements, to assess the structural characteristics, apatite-forming ability, and biodegradation of the synthesized materials. Key findings indicate that a single-phase diopside structure doped with up to 2 mol% fluoride is achievable, and an optimal fluoride content of 1 mol% yields the best biomineralization properties, attributed to the formation of fluorohydroxyapatite and the absence of fluorite (CaF2). This study demonstrates the potential of optimizing fluoride doping in Ca-Mg silicates to enhance their performance in biomedical applications, particularly in dentistry and bone regeneration. The research contributes to the field by providing a comprehensive analysis of the impact of fluoride doping on the structure and bioactivity of diopside-based ceramics. It identifies a specific fluoride concentration that significantly enhances apatite formation, a crucial property for bone and tooth regeneration. The findings highlight the delicate balance between fluoride incorporation and phase stability, demonstrating that excessive fluoride leads to the formation of undesirable phases like fluorite, which hinder biomineralization. By optimizing the material composition, the authors pave the way for the development of more effective bioceramics with tailored properties for specific biomedical applications.
Key Insights
- •Up to 2 mol% fluoride can be incorporated into diopside (MgCaSi2O6) while maintaining a single-phase structure. Above this concentration, secondary phases like fluorite and cuspidine begin to form.
- •The optimal fluoride content for biomineralization is 1 mol%. Samples with this concentration exhibited the highest apatite-forming ability in simulated body fluid (SBF) compared to undoped and 2 mol% F-doped samples.
- •Fluoride incorporation into the hydroxyapatite structure (forming fluorohydroxyapatite) enhances its chemical stability and inhibits its re-dissolution, leading to improved biomineralization, as evidenced by FTIR analysis.
- •The formation of fluorite (CaF2) in the 2 mol% F-doped sample consumes calcium ions and limits the in vitro deposition of apatite, thus reducing its biomineralization potential. This was supported by FTIR and ICP analysis.
- •ICP analysis revealed that the dissolution of Si and Mg ions from the samples increases with soaking time in SBF, indicating material degradation. Fluoride doping retards this dissolution due to the high chemical affinity of F with Si and Mg.
- •pH measurements of the SBF showed that fluoride-containing samples (1F and 2F) exhibit lower pH values compared to the undoped sample (0F) during immersion, attributed to the release of fluoride ions and their exchange with hydroxyl anions.
- •Lattice volume and crystallite size of diopside initially increase with fluoride addition (up to 2F), but decrease at higher fluoride concentrations (3F and 4F) due to fluoride depletion from diopside towards other phases (fluorite and cuspidine).
Practical Implications
- •The optimized Ca-Mg oxyfluorosilicate with 1 mol% fluoride doping has potential applications in dental root implants, bone grafts, and other biomedical devices requiring enhanced bioactivity and apatite formation.
- •Dentists and biomedical engineers can utilize these findings to develop improved dental materials, such as toothpastes, bonding agents, and root repair materials, with enhanced remineralization and caries prevention properties.
- •The inorganic salt coprecipitation method provides a scalable and cost-effective approach for synthesizing these bioceramics, making them commercially viable for various biomedical applications.
- •Future research could focus on investigating the in vivo performance of these fluoride-doped diopside ceramics in animal models to validate their efficacy in bone and tooth regeneration.
- •Further studies could explore the incorporation of other bioactive elements, such as strontium or zinc, in combination with fluoride to further enhance the biomineralization and antimicrobial properties of Ca-Mg silicates.