Addressing phosphate removal issues during peritoneal dialysis using colloidally stable iron oxide nanoclusters coated with tannic acid

Removal of chronic excess phosphates in blood is critical for patients suffering from end-stage renal disease (ESRD). ESRD patients can be treated with peritoneal dialysis (PD), during which phosphates are transported from the blood to a specific solution, named dialysate, introduced into their peritoneal cavity. However, phosphate removal in PD is currently insufficient but could be improved by introducing in dialysate phosphate adsorbents. Iron oxide nanoparticles are biocompatible and well-known effective phosphate adsorbents, but their colloidal stability at physiological pH and adsorption capacity in high ionic strength aqueous media such as dialysate are significant challenges. Here, we have evaluated the potential of tannic acid-coated iron oxide raspberry-shaped nanoclusters (RSNs@TA) for improving phosphate adsorption in dialysate. We have investigated the influence of the TA coating on phosphate adsorption by performing adsorption experiments with uncoated and TA-coated RSNs. In parallel, we have studied the influence of electrolytes and compounds in dialysate on phosphate adsorption by conducting experiments in pH 7 water and dialysate. The TA coating was shown to provide a high colloidal stability to the nanoclusters and mitigates the inhibitory effect of electrolytes in dialysate on phosphate adsorption. Indeed, electrolytes in dialysate decreased the phosphate adsorption on both nanoclusters but especially on uncoated ones by disturbing phosphate outer-sphere complexes. Thus, RSNs@TA demonstrated enhanced adsorption capacity compared to uncoated RSNs in dialysate (20.7 ± 6.4 mg P.g⁻¹) and in pH 7 water (26.4 ± 8.1 mg P.g⁻¹). These results established RSNs@TA as promising adsorbents for phosphate removal in dialysate during a PD process.