## 3 Results  
The EDS elemental composition of ACMFP particles synthesized with various fluoride contents is listed in Table 2. The fluoride concentration ranged from essentially 0 wt% in ACMP particles synthesized without fluoride to nearly 6 wt% in the particles denoted ACMFP-4. Results from ICP-OES analysis were in general agreement with EDS data for Ca, P, and Mg content, whereas fluoride ion selective electrode measurements indicated a lower F content than those quantified with EDS (Table 3). Morphology of synthesized particles is shown in Figure 1, demonstrating a generally spherical shape and a mixture of singular and fused particles with diameters ranging from 100 to 300 nm. The DLS z-average particle size of approximately 360 nm (Table 3) reflects the aggregation of particles. There were no apparent differences in the appearance between \begin{table}
\begin{tabular}{c c} \hline
**Salt** & **Conc. (mM)** \\ \hline NaCl & 30 \\ KCl & 3 \\ CaCl\({}_{2}\cdot\)2H\({}_{2}\)O & 1.5 \\ MgCl\({}_{2}\cdot\)6H\({}_{2}\)O & 0.5 \\ Na\({}_{2}\)HPO\({}_{4}\cdot\)2H\({}_{2}\)O & 2.9 \\ KH\({}_{2}\)PO\({}_{4}\) & 2.1 \\ \hline \end{tabular}
\end{table} 
Table 1: Composition of the simulated saliva solution. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Sample** & **O (wt\%)** & **Ca (wt\%)** & **P (wt\%)** & **Mg (wt\%)** & **F (wt\%)** \\ \hline ACMP & 54.3 \(\pm\) 0.8 & 23.2 \(\pm\) 1.0 & 14.6 \(\pm\) 0.1 & 7.9 \(\pm\) 1.8 & 0.1 \(\pm\) 0.1 \\ ACMFP-1 & 48.4 \(\pm\) 2.0 & 25.6 \(\pm\) 0.6 & 19.0 \(\pm\) 1.0 & 5.9 \(\pm\) 0.1 & 1.2 \(\pm\) 0.2 \\ ACMFP-2 & 50.2 \(\pm\) 1.5 & 23.0 \(\pm\) 1.5 & 17.9 \(\pm\) 2.3 & 6.4 \(\pm\) 0.4 & 2.6 \(\pm\) 0.3 \\ ACMFP-3 & 50.3 \(\pm\) 3.3 & 24.7 \(\pm\) 0.8 & 15.5 \(\pm\) 3.3 & 6.3 \(\pm\) 0.0 & 3.2 \(\pm\) 0.7 \\ ACMFP-4 & 48.6 \(\pm\) 1.8 & 25.7 \(\pm\) 1.5 & 12.8 \(\pm\) 0.6 & 7.1 \(\pm\) 0.8 & 5.8 \(\pm\) 0.2 \\ \hline \end{tabular}
\end{table} 
Table 2: Elemental composition of particles according to EDS analysis. ACMP particles (Figure 1A) and ACMFP particles (Figure 1B,C), demonstrating that the fluoride inclusion did not affect the particle morphology. XRD analysis of the same particles demonstrated that they were amorphous, with identical spectra regardless of fluoride inclusion (Figure 2A). Fluoride release, however, as shown in Figure 2B, demonstrates a significant difference between particles synthesized with and without fluoride. The relative fluoride release from particles was reflective of the concentrations listed in Table 2. The particles can be stabilized after synthesis by suspension in glycerol, with no observed changes in particle morphology or crystallinity after six months of storage at 40 \({}^{\circ}\)C.  
The gradual transformation of ACMFP particles from amorphous core-shell particles to crystalline bundles of fluoride-substituted hydroxyapatite in simulated saliva solution is shown in Figure 3A-C. In Figure 3A, protrusions of high aspect ratio crystals are observed stemming directly from the ACMFP particle surfaces, with the image capturing an early phase of the transformation process. In Figure 3B, some features of the origin of ACMFP particles are still visible, but sharp crystals dominate the appearance. In Figure 3C, the particles are completely crystallized, demonstrating the final phase of transformation. All  
Figure 1: SEM images of particles: (**A**) ACMP synthesized without fluoride; (**B**) ACMFP-2 particles; (**C**) ACMFP-4 particles. Figure 2: (**A**) XRD spectra of ACMP, ACMFP-2, and ACMFP-4 particles; (**B**) Fluoride release curves from ACMP and ACMFP particles with varied fluoride content. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & **Ca (wt\%)** & **P (wt\%)** & **Mg (wt\%)** & **F (wt\%)** & **Z-Avg. Particle** & **BET Surface** \\  & & & & & **Size (nm)** & **Area (g/m\({}^{2}\))** \\ \hline ACMFP-2 & 21.5 \(\pm\) 0.3 & 20.0 \(\pm\) 0.5 & 6.9 \(\pm\) 0.1 & 1.51 \(\pm\) 0.05 & 362 \(\pm\) 38 & 24.5 \(\pm\) 1.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Characteristics of ACMFP-2 particles.