Furthering the understanding of silicate-substitution in a-tricalcium phosphate: An X-ray diffraction, X-ray fluorescence and solid-state nuclear magnetic resonance study

J. Duncan*, S. Hayakawa, A. Osaka, J. F. MacDonald, J. V. Hanna, J. M. S. Skakle, I. R. Gibson

*Corresponding author for this work

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Abstract

High-purity (SupT) and reagent-grade (ST), stoichiometric and silicate-containing a-tricalcium phosphate (alpha-TCP: STO/SupTO and Si-TCP x = 0.10: ST10/SupT10) were prepared by solid-state reaction based on the substitution mechanism Ca-3(PO4)((2-x))(SiO4)(x). Samples were determined to be phase pure by X-ray diffraction (XRD), and Rietveld analysis performed on the XRD data confirmed inclusion of Si in the alpha-TCP structure as determined by increases in unit cell parameters; particularly marked increases in the b-axis and beta-angle were observed. X-ray fluorescence (XRF) confirmed the presence of expected levels of Si in Si-TCP compositions as well as significant levels of impurities (Mg, Al and Fe) present in all ST samples; SupT samples showed both expected levels of Si and a high degree of purity. Phosphorus (P-31) magic-angle-spinning solid-state nuclear magnetic resonance (MAS NMR) measurements revealed that the high-purity reagents used in the synthesis of SupTO can resolve the 12 expected peaks in the P-31 spectrum of a-TCP compared to the low-purity STO that showed significant spectral line broadening; line broadening was also observed with the inclusion of Si which is indicative of induced structural disorder. Silicon (Si-29) MAS NMR was also performed on both Si-TCP samples which revealed Q(0) species of Si with additional Si Q(1)/Q(2) species that may indicate a potential charge-balancing mechanism involving the inclusion of disilicate groups; additional Q(4) Si species were also observed, but only for ST10. Heating and cooling rates were briefly investigated by P-31 MAS NMR which showed no significant line broadening other than that associated with the emergence of beta-TCP which was only realised with the reagent-grade sample STO. This study provides an insight into the structural effects of Si-substitution in alpha-TCP and could provide a basis for understanding how substitution affects the physicochemical properties of the material. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Original languageEnglish
Pages (from-to)1443-1450
Number of pages8
JournalActa Biomaterialia
Volume10
Issue number3
Early online date25 Nov 2013
DOIs
Publication statusPublished - Mar 2014

Keywords

  • Ca3(PO4)2
  • silicon
  • bioceramics
  • Rietveld
  • Si-29
  • P-31
  • stabilized calcium phosphates
  • in-vivo behavior
  • hydroxyapatite granules
  • powder diffraction
  • alpha
  • NMR
  • temperature
  • ALPHA-CA3(PO4)2

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