Fluoride Release of Engineered Fluoride Nanoparticles at Different pHs

Objectives: To increase the retention of fluoride in the dental biofilm, we have engineered positively-charged fluoride nanoparticles from different fluoride salts: CaF₂ (low solubility) and SnF₂ (high solubility). Here we test the ability of these formulations to release fluoride at different pHs.
Methods: Nanoparticles (<200 nm) were prepared from chitosan (Chit) and the respective fluoride salt by electrohydrodynamic jetting. ChitCaF₂ and ChitSnF₂ nanoparticle suspensions were dispensed into dialysis tubes and immersed at pHs 6.5, 6.0, 5.5, 5.0, and 4.5 (prepared from different 0.1 M buffers: phosphate and cacodylate for the 2 highest pHs and acetate for the others), at 37^oC. Dialysis tubes were transferred to fresh buffers at different time points, and fluoride release was determined using a fluoride electrode.
Results: The ChitCaF₂np exhibited a pH-dependent fluoride release; the percentage released after 24 h increased from around 7% of total fluoride in the suspension at pH 6.5 (phosphate buffer) to around 70% at pH 4.5 (acetate buffer). These particles presented a reduced solubility in phosphate buffer when compared to cacodylate buffer (at 24 h, pH 6.5: phosphate=7.2%, cacodylate=18.2% of total fluoride released; pH 6.0: phosphate=7.7%, cacodylate=29.6% of total fluoride released). At all pHs, only around 1% of total fluoride was released in the first hour. The ChitSnF₂np, on the other hand, presented a quick fluoride release, which was not affected by the pH: at 1 h, at least 25% of the total fluoride in these particles had been released; this increased to at least 75% at 24 h.
Conclusions: The formulated fluoride nanoparticles exhibited either a quick or a more slow, pH-dependent fluoride release, suggesting they can be used to formulate intelligent anticaries treatments with sustainable delivery of fluoride ions to the dental biofilm.