title: Surface modification of hydroxyapatite. Part II. Silica.
abstract: Nanophase hydroxyapatite (HAP) particles were coated with varying amounts of silica (5-75wt%) via the hydrolysis of tetraethyl orthosilicate. The nanocomposite particles were characterized by transmission electron spectroscopy, X-ray diffraction (XRD), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), BET N(2) gas adsorption, sedimentation time studies, acid dissolution, and zeta potential (zeta). A sequential decrease in infrared spectral features characteristic of HAP was accompanied by an increase in features characteristic of silica as revealed by DRIFTS. The specific surface area of the silica-coated HAP particles showed a non-systematic increase. In comparison to the uncoated HAP (50m(2)/g), silica coatings of 5, 25, 50 and 75wt% yielded specific surface areas of 55, 93, 70, and 138m(2)/g, respectively. This behavior can be explained based on a heterocoagulation coating mechanism in which silica clusters of approximately 14nm in diameter adsorb onto the HAP particle surface. The decrease in specific surface area at 50wt% silica corresponded to the attainment of a complete surface coating. This conclusion was substantiated by the observed resistance of these particles to dissolution in 1M HCl. However, the acid treatment transformed the silica-coated HAP core particles to CaCl(2).Ca(H(2)PO(4))(2).2H(2)O (calcium chloride phosphate hydrate) based on XRD analysis.
authors.affiliation: Biomimetics, Orthopedics, and Nanomaterials Exploration (BONE) Lab, Department of Materials and Nuclear Engineering, University of Maryland, 20742, College Park, MD, USA.
authors.forename: L
authors.initials: L
authors.lastname: Borum
authors.forename: O C
authors.initials: OC
authors.lastname: Wilson
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry; D017886:Durapatite / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D008854:Microscopy, Electron; D008956:Models, Chemical; D012821:Silanes / Q000737:chemistry*; D012822:Silicon Dioxide / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013499:Surface Properties; D014961:X-Ray Diffraction
chemical_list: D001672:Biocompatible Materials; D012821:Silanes; C040733:tetraethoxysilane; D012822:Silicon Dioxide; D017886:Durapatite