Nanostructured porous hollow ellipsoidal capsules of hydroxyapatite and calcium silicate: preparation and application in drug delivery

We have successfully prepared for the first time hydroxyapatite (HAp) and calcium silicate (CaSiO(3)) nanostructured porous hollow ellipsoidal capsules which are constructed by nanoplate networks using the inorganic CaCO(3) template. CaCO(3) ellipsoids are synthesized via the reaction between Ca(CH(3)COO)(2) and NaHCO(3) in water and ethylene glycol mixed solvent at room temperature and they are used as the Ca(2+) source and cores. Then a PO(4)(3-) or SiO(3)(2-) source is added to react with CaCO(3) to form a HAp or CaSiO(3) shell on the surface of CaCO(3) ellipsoids. Dilute acetic acid is used to remove remaining CaCO(3) cores. The size and shape of the HAp and CaSiO(3) hollow capsules are determined by those of the cores. The thickness of the capsule shell can be controlled by adjusting the concentration of PO(4)(3-) or SiO(3)(2-) source. A number of PO(4)(3-) sources such as dilute H(3)PO(4), Na(3)PO(4) and Na(2)HPO(4) can be used to form HAp hollow capsules with similar morphologies. The drug loading and release behavior of HAp hollow capsules is also investigated. A typical anti-inflammatory drug, ibuprofen, is used for drug loading. The result indicates that HAp hollow capsules have a high specific surface area and high storage capacity, and favorable drug release behavior.