title: Biomimetic apatite coatings--carbonate substitution and preferred growth orientation.
abstract: Biomimetic apatite coatings were obtained by soaking chemically treated titanium in SBF with different HCO(3)(-) concentration. XRD, FTIR and Raman analyses were used to characterize phase composition and degree of carbonate substitution. The microstructure, elemental composition and preferred alignment of biomimetically precipitated crystallites were characterized by cross-sectional TEM analyses. According to XRD, the phase composition of precipitated coatings on chemically pre-treated titanium after exposure to SBF was identified as hydroxy carbonated apatite (HCA). A preferred c-axis orientation of the deposited crystals can be supposed due to the high relative peak intensities of the (002) diffraction line at 2theta=26 degrees compared to the 100% intensity peak of the (211) plane at 2theta=32 degrees . The crystallite size in direction of the c-axis of HCA decreased from 26 nm in SBF5 with a HCO(3)(-) concentration of 5 mmol/l to 19 nm in SBF27 with a HCO(3)(-) concentration of 27 mmol/l. Cross-sectional TEM analyses revealed that all distances correspond exactly to the hexagonal structure of hydroxyapatite. The HCO(3)(-) content in SBF also influences the composition of precipitated calcium phosphates. Biomimetic apatites were shown to have a general formula of Ca(10-x-y)Mg(y)(HPO(4))(x-z)(CO(3))(z)(PO(4))(6-x)(OH)(2-x-w)(CO(3))(w/2). According to FTIR and Raman analyses, it can be supposed that as long as the HCO(3)(-) concentration in the testing solutions is below 20 mmol/l, only B-type HCA (0<z<1; w=0) precipitates. At higher HCO(3)(-) concentration, it can be assumed that AB-type HCA (z=1;0<w<1) is formed.
authors.affiliation: University of Erlangen-Nuernberg, Department of Materials Science - Biomaterials, Henkestr. 91, D-91052 Erlangen, Germany.
authors.forename: Lenka
authors.initials: L
authors.lastname: Müller
authors.forename: Egle
authors.initials: E
authors.lastname: Conforto
authors.forename: Daniel
authors.initials: D
authors.lastname: Caillard
authors.forename: Frank A
authors.initials: FA
authors.lastname: Müller
mesh_terms: D001031:Apatites / Q000737:chemistry*; D032701:Biomimetics; D001826:Body Fluids / Q000737:chemistry; D002254:Carbonates / Q000737:chemistry*; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D008422:Materials Testing; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D010316:Particle Size; D013499:Surface Properties; D014025:Titanium / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D001031:Apatites; D002254:Carbonates; D020099:Coated Materials, Biocompatible; D014025:Titanium