Organic modification of layered zirconium phosphate/phosphonate for controlled release of therapeutic inorganic ions

Abstract

The present study aims to develop a layered zirconium phosphate/phosphonate (LZP) powder to control the release of therapeutic inorganic ions. Organically modified LZPs were successfully prepared with various contents of phenyl groups via a reflux method in an aqueous solution containing phosphoric and phenylphosphonic acids. Powder X-ray diffraction analysis and Fourier transform infrared spectroscopy revealed that the crystal structure of the synthesized LZP samples was identical to that of α-zirconium phosphate, even after modification. The amount of incorporated organic molecules increased with increasing molar fractions of phenylphosphonic acid in the starting composition, as determined from the thermal analysis. Cobalt ion (Co²⁺), a type of therapeutic inorganic ion, was incorporated into the organically modified LZP through treatment with an acetonitrile solution containing tetrabutylammonium ions, followed by treatment with an acetonitrile solution containing CoCl₂. The amount of incorporated Co²⁺ depended on the concentration of the phenyl groups. Furthermore, the highest amount of Co²⁺ was incorporated in the sample (ZP-Ph-0.5) prepared with equimolar phosphoric/phenylphosphonic acid. The ZP-Ph-0.5 sample additionally showed the ability to incorporate copper or iron ions (Cu²⁺ or Fe³⁺). The incorporated ion, either Co²⁺ or Cu²⁺, was continuously released from the ZP-Ph-0.5 sample in a saline solution over a period of three weeks, whereas the release of Fe³⁺ was negligible. The quantity of Co²⁺ released was higher than that of Cu²⁺. The controlled release of Co²⁺ from the ZP-Ph-0.5 sample was also observed in a simulated body fluid that mimicked the ionic concentration of human blood plasma. These results confirm that a specific degree of phenyl modification makes LZP a candidate host material for releasing therapeutic inorganic ions.

Keywords: 100 Materials, 301 Chemical syntheses / processing; 107 Glass and ceramic materials; 200 Applications; 211 Scaffold / Tissue engineering / Drug delivery; 30 Bio-inspired and biomedical materials; 300 Processing / Synthesis and Recycling; Biomaterials; intercalation; layered zirconium phosphate/phosphonate; tetrabutylammonium; therapeutic inorganic ions.