Lack of OH in nanocrystalline apatite as a function of degree of atomic order: Implications for bone and biomaterials

Jill Dill Pasteris, Brigitte Wopenka, John J. Freeman, Keith Rogers, Eugenia Valsami-Jones, Jacqueline A.M. Van Der Houwen, Matthew J. Silva

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283 Scopus citations

Abstract

Using laser Raman microprobe spectroscopy, we have characterized the degree of hydroxylation and the state of atomic order of several natural and synthetic calcium phosphate phases, including apatite of biological (human bone, heated human bone, mouse bone, human and boar dentin, and human and boar enamel), geological, and synthetic origin. Common belief holds that all the studied phases are hydroxylapatite, i.e., an OH-containing mineral with the composition Ca10(PO4)6(OH)2. We observe, however, that OH-incorporation into the apatite crystal lattice is reduced for nanocrystalline samples. Among the biological samples, no OH-band was detected in the Raman spectrum of bone (the most nanocrystalline biological apatite), whereas a weak OH-band occurs in dentin and a strong OH-band in tooth enamel. We agree with others, who used NMR, IR spectroscopy, and inelastic neutron scattering, that - contrary to the general medical nomenclature - bone apatite is not hydroxylated and therefore not hydroxylapatite. Crystallographically, this observation is unexpected; it therefore remains unclear what atom(s) occupy the OH-site and how charge balance is maintained within the crystal. For non-bone apatites that do show an OH-band in their Raman spectra, there is a strong correlation between the concentration of hydroxyl groups (based on the ratio of the areas of the 3572Δcm -1 OH-peak to the 960Δcm-1 P-O phosphate peak) and the crystallographic degree of atomic order (based on the relative width of the 960Δcm-1 P-O phosphate peak) of the samples. We hypothesize that the body biochemically imposes a specific state of atomic order and crystallinity (and, thus, concentration of hydroxyl) on its different apatite precipitates (bone, dentin, enamel) in order to enhance their ability to carry out tissue-specific functions.

Original languageEnglish
Pages (from-to)229-238
Number of pages10
JournalBiomaterials
Volume25
Issue number2
DOIs
StatePublished - Jan 2004

Keywords

  • Apatite structure
  • Biomineralization
  • Bone
  • Calcium phosphate
  • Crystallinity
  • Raman spectroscopy

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    Pasteris, J. D., Wopenka, B., Freeman, J. J., Rogers, K., Valsami-Jones, E., Van Der Houwen, J. A. M., & Silva, M. J. (2004). Lack of OH in nanocrystalline apatite as a function of degree of atomic order: Implications for bone and biomaterials. Biomaterials, 25(2), 229-238. https://doi.org/10.1016/S0142-9612(03)00487-3