A Perfluorocarbon-Coated ZrP Cation Exchanger with Excellent Ammonium Selectivity and Chemical Stability: An Oral Sorbent for End-Stage Kidney Disease (ESKD).

Abstract

An oral sorbent to remove NH4+ within the small intestine of end-stage kidney disease (ESKD) patients could reduce blood urea levels and diminish their dialysis treatment burden. But current sorbent materials like amorphous zirconium phosphate particles Zr(HPO4)2·H2O (ZrP) lack the selectivity to remove NH4+ in water solution with other competing ions. Our previous work found that a gas-permeable, hydrophobic polydimethylsiloxane (PDMS) coating on ZrP improved the material's selectivity for NH4+. However, a competing ion Ca2+ was still removed by PDMS-coated ZrP sorbent, and the permeability of the PDMS coating to Ca2+ was increased after low-pH stomach-like condition exposure. An alternative hydrophobic and gas permeable coating has been investigated─perfluorooctyltriethoxysilane (FOTS). The coating was attached in place of PDMS to a tetraethyl orthosilicate-coated ZrP surface. Surface atomic composition analysis and scanning electron microscopy observation verified the successful application of the FOTS coating. Water contact angle analysis validated the FOTS coating was hydrophobic (145.0 ± 3.2°). In vitro competing ion studies indicated the FOTS coating attached to ZrP increased NH4+ removal by 53% versus uncoated ZrP. FOTS offers complete selectivity for NH4+ over Ca2+ with similar NH4+ capacity as the previous PDMS coating. Moreover, FOTS-coated ZrP maintained NH4+ removal capacity and selectivity after the acid exposure study, indicating excellent acid resistance while NH4+ selectivity of ZrP-PDMS decreased by 72%. The results suggested that FOTS-coated ZrP is promising as an oral sorbent for ESKD patients.