title: Structural studies of bioactivity in sol-gel-derived glasses by X-ray spectroscopy.
abstract: Extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge structure, X-ray fluorescence spectroscopy, and X-ray powder diffraction have been used to study the local calcium environment in four sol-gel-derived bioactive calcium silicate glasses of the general formula (CaO)(x)(SiO(2))(1-x). The formation of a hydroxyapatite layer on the composition with the highest bioactivity (x = 0.3) with time has been studied, in an in vitro environment, by immersion in simulated body fluid (SBF) at 37 degrees C. The calcium oxygen environment in the four compositions has been shown to be six-coordinate in character. Both the extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge structure show a gradual increase in coordination number and Ca--O bond distance with longer exposure to SBF. X-ray fluorescence show that calcium is quickly lost from the samples on exposure to SBF and the calcium concentration then recovers with time. There is clear evidence that the recovery of calcium content is due to the formation of a CaO-P(2)O(5)-rich layer. Annealing of samples at 650 degrees C shows the presence of what, on the length scales probed by X-ray diffraction, appears to be noncrystalline calcium phosphate after 1 h of exposure to an SBF solution, which becomes more crystalline on longer exposure.
authors.affiliation: School of Physical Sciences, University of Kent, Canterbury, CT2 7NR, United Kingdom. ljs32@kent.ac.uk
authors.forename: Laura J
authors.initials: LJ
authors.lastname: Skipper
authors.forename: Frank E
authors.initials: FE
authors.lastname: Sowrey
authors.forename: David M
authors.initials: DM
authors.lastname: Pickup
authors.forename: Victoria
authors.initials: V
authors.lastname: Fitzgerald
authors.forename: Rumana
authors.initials: R
authors.lastname: Rashid
authors.forename: Kieran O
authors.initials: KO
authors.lastname: Drake
authors.forename: Zhongjie
authors.initials: Z
authors.lastname: Lin
authors.forename: Priya
authors.initials: P
authors.lastname: Saravanapavan
authors.forename: Larry L
authors.initials: LL
authors.lastname: Hench
authors.forename: Mark E
authors.initials: ME
authors.lastname: Smith
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Newport
mesh_terms: D001672:Biocompatible Materials / Q000737:chemistry*; D001826:Body Fluids; D017610:Calcium Compounds / Q000737:chemistry; D005782:Gels; D005898:Glass / Q000737:chemistry*; D066298:In Vitro Techniques; D008422:Materials Testing; D017640:Silicates / Q000737:chemistry; D013057:Spectrum Analysis; D014961:X-Ray Diffraction; D014965:X-Rays
chemical_list: D001672:Biocompatible Materials; D017610:Calcium Compounds; D005782:Gels; D017640:Silicates; C031293:calcium silicate