title: Hydrogen-substituted β-tricalcium phosphate synthesized in organic media.
abstract: β-Tricalcium phosphate (β-TCP) platelets synthesized in ethylene glycol offer interesting geometries for nano-structured composite bone substitutes but were never crystallographically analyzed. In this study, powder X-ray diffraction and Rietveld refinement revealed a discrepancy between the platelet structure and the known β-TCP crystal model. In contrast, a model featuring partial H for Ca substitution and the inversion of P1O4tetrahedra, adopted from the whitlockite structure, allowed for a refinement with minimal misfits and was corroborated by HPO42-absorptions in Fourier-transform IR spectra. The Ca/P ratio converged to 1.443 ± 0.003 (n = 36), independently of synthesis conditions. As a quantitative verification, the platelets were thermally decomposed into hydrogen-free β-TCP and β-calcium pyrophosphate which resulted in a global Ca/P ratio in close agreement with the initial β-TCP Ca/P ratio (ΔCa/P = 0.003) and with the chemical composition measured by inductively coupled plasma (ΔCa/P = 0.003). These findings thus describe for the first time a hydrogen-substituted β-TCP structure, i.e. a Mg-free whitlockite, represented by the formula Ca21 - x(HPO4)2x(PO4)14 - 2x, where x = 0.80 ± 0.04, and may have implications for resorption properties of bone regenerative materials.
authors.affiliation: RMS Foundation, Bettlach, Switzerland.
authors.forename: Christoph
authors.initials: C
authors.lastname: Stähli
authors.affiliation: RMS Foundation, Bettlach, Switzerland.
authors.forename: Jürg
authors.initials: J
authors.lastname: Thüring
authors.affiliation: RMS Foundation, Bettlach, Switzerland.
authors.forename: Laëtitia
authors.initials: L
authors.lastname: Galea
authors.affiliation: MATEIS, INSA-Lyon, Villeurbanne CEDEX, France.
authors.forename: Solène
authors.initials: S
authors.lastname: Tadier
authors.affiliation: RMS Foundation, Bettlach, Switzerland.
authors.forename: Marc
authors.initials: M
authors.lastname: Bohner
authors.affiliation: RMS Foundation, Bettlach, Switzerland.
authors.forename: Nicola
authors.initials: N
authors.lastname: Döbelin
keywords: Rietveld refinement; X-ray diffraction; bone substitute; calcium deficiency; whitlockite; β-tricalcium phosphate