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

Abstract

We have successfully prepared for the first time hydroxyapatite (HAp) and calcium silicate (CaSiO₃) nanostructured porous hollow ellipsoidal capsules which are constructed by nanoplate networks using the inorganic CaCO₃ template. CaCO₃ ellipsoids are synthesized via the reaction between Ca(CH₃COO)₂ and NaHCO₃ in water and ethylene glycol mixed solvent at room temperature and they are used as the Ca²⁺ source and cores. Then a PO₄³⁻ or SiO₃²⁻ source is added to react with CaCO₃ to form a HAp or CaSiO₃ shell on the surface of CaCO₃ ellipsoids. Dilute acetic acid is used to remove remaining CaCO₃ cores. The size and shape of the HAp and CaSiO₃ hollow capsules are determined by those of the cores. The thickness of the capsule shell can be controlled by adjusting the concentration of PO₄³⁻ or SiO₃²⁻ source. A number of PO₄³⁻ sources such as dilute H₃PO₄, Na₃PO₄ and Na₂HPO₄ 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.