This research focuses on the synthesis of composite CoFe2O4 (CoF) nanoparticles coated with SiO2 using hydroxyapatite (HAP) as a template (CoFSi) and the pH controlled release of indomethacin (IMC) drug from this nanocomposite. The formation of the CoFe2O4-HAp (CoFHAp) nanoparticles and of the CoFe2O4@SiO2 (CoFSi) nanoparticles were monitored using XRD, FT-IR, that TEM, SEM, and ED studies. The magnetic properties are measured with a VSM. The TEM images showed the CoFe2O4 to have a core-shell structure encapsulated by a silica coating with an average size of 50 nm. BET showed the mean pore sizes of the silica shell to be approximately 10-20 nm and the surface area to be 212.8 m(2) g(-1). Magnetization (M-s) and remnant (M-r) magnetic properties of CoFSi nanocomposite decreased upon silica coating (from similar to 14 to 2 emu g(-1) for Ms of CoF and CoFSi, respectively). In contrast, the coercivity (H-c) of the uncoated CoFe2O4 (317 Oe) is lower than that of the coated nanocomposites (1250 Oe of CoFSi). In vitro drug loading of the CoFSi nanoparticles and its pH-responsive (pH = 4.0 and 7.0) controlled release were investigated using IMC as a model drug. It was seen that the release of the IMC drug was significantly faster at a pH of 4.0 compared to that at a neutral pH 7.0. Furthermore, the lower concentration of ions release (iron and cobalt) from CoFSi was observed after aging for 50 h. (C) 2011 Elsevier B.V. All rights reserved.