Synthesis and structural characterization of Sr(II) ion-containing octacalcium phosphate incorporated with both 2,6-pyridinedicarboxylate and succinate ions as a bone defect filler with multiple drug loading capability

Structural characterization of cation-containing octacalcium phosphate (OCP) samples incorporated with dicarboxylate ions is important to gain insight into their potential as a novel bone defect filler with loading capability of physiologically and pharmacologically active substances. In this study, Sr²⁺-containing OCP (SrOCPC) samples incorporated with both 2,6-pyridinedicarboxylate (PA) ions and succinate (SA) ions were successfully synthesized. For comparison, OCP samples without Sr²⁺ (OCPC) were also synthesized. ¹³C NMR analysis of the dicarboxylate ions in the samples showed that only anionic PA was incorporated in the synthesized samples at PA/(PA+SA) molar ratios above 0.1, whereas both anionic PA and SA were incorporated only at a molar ratio of 0.01. Additionally, the PA content of the SrOCPC and OCPC samples was almost the same at the molar ratio of 0.01. We demonstrated for the first time that the SrOCPC sample at a PA/(PA+SA) molar ratio of 0.01 has the potential to be a novel bone defect filler with multiple drug loading capability of PA, SA, and Sr²⁺.