Synthesis of sodium caseinate-calcium carbonate microspheres and their mineralization to bone-like apatite

摘要

Phosphoproteins can induce and stabilize calcium carbonate (CaCO_3) vaterite, which has desirable features for high reactivity. The purpose of this study was to synthesize bioactive CaCO_3 microspheres for bone regeneration. Sodium caseinate (NaCas)-containing CaCO_3 microspheres, with the crystal phase of vaterite, were synthesized by fast precipitation in an aqueous solution of CaCl_2, Na_2CO_3, and 2 mg/mL of NaCas. The uniform microspheres exhibited rougher surfaces and lower negative charges than CaCO_3 particles without NaCas addition. Fourier-transform infrared spectroscopy (FT-IR) of the microspheres showed characteristic peaks or bands corresponding to phosphate and hydroxyl groups. Thermogravi-metric analysis (TGA) curves exhibited approximately 5% weight loss below 600 ℃ due to the decomposition of NaCas. Scanning electron microscope (SEM) images showed lath-like hydroxyapatite (HAp) on the surface after soaking in simulated body fluid (SBF) at 37 ℃ for 5 and 10 days. Energy dispersive X-ray spectrometry (EDS) revealed that the agglomerates were composed of Ca, C, O, P, Na, and Mg elements, and the Ca/P ratios ranged from 1.53 to 1.56. X-ray diffraction (XRD) patterns exhibited peaks characteristic of hydroxyapatite. The results of this study demonstrated that the addition of NaCas induced the formation of vaterite microspheres which possesses an enhanced apatite formation after soaking in SBF at 37 ℃ for 5 and 10 days. These NaCas-CaCO_3 microspheres may be a potential biomaterial for bone regeneration.